The fluoride anion plays an important role in dental health and as a result is added to drinking water at low concentrations. If the concentration of fluoride is too high however, skeletal fluorosis can occur. Because of this, there has been significant interest in the development of water compatible anion sensors that can sense fluoride at the ppm level. This is made difficult by the high hydration enthalpy of fluoride (ΔH0 = -504 KJ/mol) which significantly lowers the reactivity of this anion in water. For this reason it has become the goal of the Gabbaï group, as well as other research groups to develop fluoride sensing small molecules. Such molecules should possess sufficient Lewis acidity to overcome the hydration enthalpy of the fluoride anion. A significant amount of research has been conducted on triarylboranes containing cationic moieties such as ammonium, phosphonium, and sulfonium groups. This thesis will describe additional examples of such species, including a series of ammonium boranes of the general formula [p-(Mes2B)C6H4(NMe2R)]+. As indicated by anion complexation studies, the R group present in these molecules has a notable effect on the anion affinity of the somewhat distant boron center. Another component of this thesis deals with the chemistry of newly synthesized stiboranes that are also decorated by peripheral ammonium groups. As observed for the ammonium boranes mentioned above, the ammonium groups present in these stiboranes drives anion capture, leading to zwitterionic ammonium antimonite formation.

Chapter 1 Thermally activated delayed fluorescence (TADF) materials provide a strategy to improve external quantum efficiencies of organic light emitting diodes (OLEDs). Because of spin-statistics, 25% singlet and 75% triplet excitons are generated in an electronic device. Conventional organic emitters cannot harvest the triplet excitons, due to low spin orbit coupling, and exhibit low external quantum efficiencies. TADF materials have to be designed in such a way, that the energy gap between the lowest singlet and triplet states (ΔES-T) is sufficiently small to allow reverse intersystem crossing (rISC) in organic systems. An established structure property relationship for the generation of TADF materials is the spatial separation of HOMO and LUMO via an orthogonal arrangement of donor and acceptor in donor-π-acceptor (D-π-A) compounds. This is achieved by increasing the steric bulk of the π-bridge. However, this is not always the most efficient method and electronic parameters have to be considered. In a combined experimental and theoretical study, a computational protocol to predict the excited states in D-π-A compounds containing the B(FXyl)2 (FXyl = 2,6-bis(trifluoromethyl)phenyl) acceptor group for the design of new TADF emitters is presented. To this end, the effect of different donor and π-bridge moieties on the energy gaps between local and charge-transfer singlet and triplet states was examined. To prove the computationally aided design concept, the D-π-B(FXyl)2 compounds Cbz-π (1), Cbz-Meπ (2), Phox-Meπ (3), Phox-MeOπ (4), and MeO₃Ph-FMeπ (5) were synthesized and fully characterized. The photophysical properties of these compounds in various solvents, polymeric film and in a frozen matrix were investigated in detail and show excellent agreement with the computationally obtained data (Figure 5.1). A simple structure-property relationship based on the molecular fragment orbitals of the donor and the π-bridge which minimize the relevant singlet-triplet gaps to achieve efficient TADF emitters is presented.   Chapter 2 Three-coordinate boron is widely used as an acceptor in conjugated materials. In recent years the employment of trifluoromethylated aryls was shown to improve the acceptor properties of such boranes. Astonishingly, the use of ortho-trifluoromethylated aryls in boron containing systems also improves the stability of those systems in regard to their inherent reactivity towards nucleophiles. Borafluorenes are stronger acceptors than their non-annulated triarylborane derivatives. In previous studies, the effect of trifluoromethylated aryls as the exo-aryl moieties in borafluorenes, as well as the effect of fluorination on the backbone, were examined. As the latter suffers from a very low stability, systems using trifluoromethyl groups, both on the exo-aryl as well as the borafluorene backbone were designed in order to maximize both the stability as well as the acceptor strength. Three different perfluoroalkylated borafluorenes were prepared and their electronic and photophysical properties were investigated. The systems have four trifluoromethyl moieties on the borafluorene moiety as well as two trifluoromethyl groups at the ortho positions of their exo-aryl moieties. They differ with regard to the para-substituents on their exo-aryl moieties, being a proton (FXylFBf), a trifluoromethyl group (FMesFBf) or a dimethylamino group (p NMe2-FXylFBf), respectively. Furthermore, an acetonitrile adduct of FMesFBf was obtained and characterized. All derivatives exhibit extraordinarily low reduction potentials, comparable to those of perylenediimides. The most electron deficient derivative FMesFBf was also chemically reduced and its radical anion isolated and characterized. Furthermore, the photophysical properties of all compounds were investigated. All compounds exhibit weakly allowed lowest energy absorptions and very long fluorescent lifetimes of ca. 250 ns up to 1.6 μs; however, the underlying mechanisms differ. The donor substituted derivative p-NMe2-FXylFBf exhibits thermally activated delayed fluorescence from a charge transfer (CT) state, while the FMesFBf and FXylFBf borafluorenes exhibit only weakly allowed locally excited (LE) transitions due to their symmetry and low transition dipole moments, as suggested by DFT and TD-DFT calculations.   Chapter 3 Conjugated dendrimers find wide application in various fields, such as charge transport/storage or emitter materials in organic solar cells or OLEDs. Previous studies on boron containing conjugated dendrimers are scarce and mostly employ a convergent synthesis approach, lacking a simple, generally applicable synthetic access. A new divergent approach was designed and conjugated triarylborane dendrimers were synthesized up to the 2nd generation. The synthetic strategy consists of three steps: 1) functionalization, via iridium catalyzed C–H borylation; 2) activation, via fluorination of the generated boronate ester with K[HF2] or [N(nBu)4][HF2]; and 3) expansion, via reaction of the trifluoroborate salts with aryl Grignard reagents. The concept was also shown to be viable for a convergent approach. All but one of the conjugated borane dendrimers exhibit multiple, distinct and reversible reduction potentials, making them potentially interesting materials for applications in molecular accumulators (Figure 5.7). Based on their photophysical properties, the 1st generation dendrimers exhibit good conjugation over the whole system. The conjugation does not further increase upon expansion to the 2nd generation, but the molar extinction coefficients increase linearly with the number of triarylborane sub-units, suggesting a potential application as photonic antennas.   Chapter 4 A surprisingly high electronically-driven regioselectivity for the iridium-catalyzed C–H borylation using [Ir(COD)OMe]2 (COD = 1,5-cyclooctadiene) as the precatalytic species, bis(pinacolato)diboron (B2pin2) as the boron source and 4,4’-ditertbutyl-2,2’-bipyridin (dtbpy) as the ligand of D-π-A systems with diphenylamino (1) or carbazolyl (2) moieties as the donor, bis(2,6-bis(trifluoromethyl)phenyl)boryl (B(FXyl)2) as the acceptor, and 1,4-phenylene as the π-bridge was observed. Under these conditions, borylation was observed only at the sterically least encumbered para-positions of the acceptor groups. As boronate esters are versatile building blocks for organic synthesis (C–C coupling, functional group transformations), the C–H borylation represents a simple potential method for post-functionalization by which electronic or other properties of D-π-A systems can be fine-tuned for specific applications. The photophysical and electrochemical properties of the borylated (1-(Bpin)2) and unborylated (1) diphenylamino-substituted D-π-A systems were investigated. Interestingly, the borylated derivative exhibits coordination of THF to the boronate ester moieties, influencing the photophysical properties and exemplifying the non-innocence of boronate esters. / Kapitel 1 Materialien mit thermisch aktivierter verzögerter Fluoreszenz (TADF) eröffnen einen Weg zur Verbesserung der externen Quanteneffizienz von organischen Leuchtdioden (OLEDs). Aufgrund der Spin-Statistik werden in einem elektronischen Bauelement 25% Singulett- und 75% Triplett-Exzitonen erzeugt. Konventionelle organische Emitter können Triplett-Exzitonen aufgrund ihrer geringen Spin-Bahnkopplung nicht nutzen und weisen niedrige externe Quanteneffizienzen auf. TADF-Materialien müssen so entworfen werden, dass die Energielücke zwischen dem niedrigsten Singulett- und dem niedrigsten Triplett-Zustand (ΔES T) ausreichend klein ist, um Rück-Interkombination (rISC) in organischen Systemen zu ermöglichen (Schema 5.1). Eine etablierte Struktur-Eigenschafts-Beziehung für die Erzeugung von TADF-Materialien ist die räumliche Trennung von HOMO und LUMO über eine orthogonale Anordnung von Donor und Akzeptor in Donor-π-Akzeptor-Verbindungen (D-π-A). Dies wird durch eine Vergrößerung des sterischen Anspruchs der π-Brücke erreicht. Dies ist jedoch nicht immer die effizienteste Methode und elektronische Parameter müssen berücksichtigt werden. In einer kombinierten experimentellen und theoretischen Studie wird ein Berechnungsprotokoll zur Vorhersage der angeregten Zustände in D-π-A-Verbindungen, die die Akzeptorgruppe B(FXyl)2 (FXyl = 2,6-Bis(trifluoromethyl)phenyl) enthalten, für das Design neuer TADF-Emitter vorgestellt. Zu diesem Zweck wurde die Wirkung verschiedener Donor- und π-Brückeneinheiten auf die Energielücken zwischen lokalen und ladungsübertragenden Singulett- und Triplett-Zuständen untersucht. Um das durch quantenchemische Rechnungen gestützte Designkonzept zu beweisen, wurden die D-π-B(FXyl)2-Verbindungen Cbz-π (1), Cbz-Meπ (2), Phox-Meπ (3), Phox-MeOπ (4) und MeO₃Ph-FMeπ (5) synthetisiert und vollständig charakterisiert. Die photophysikalischen Eigenschaften dieser Verbindungen in verschiedenen Lösungsmitteln, im Polymerfilm und in einer gefrorenen Glas-Matrix wurden im Detail untersucht und zeigen eine ausgezeichnete Übereinstimmung mit den berechneten Daten. Eine einfache Struktur-Eigenschafts-Beziehung wird vorgestellt, die auf den molekularen Fragment-Orbitalen des Donors und der π-Brücke basiert, welche die relevanten Singulett-Triplett-Lücken minimieren, um effiziente TADF-Emitter zu erhalten.   Kaptiel 2 Dreifach koordiniertes Bor ist als Akzeptor in konjugierten Materialien weit verbreitet. In den letzten Jahren hat sich gezeigt, dass der Einsatz trifluoromethylierter Aromaten die Akzeptoreigenschaften solcher Borane verbessert. Erstaunlicherweise verbessert die Verwendung von ortho-trifluormethylierten Aromaten in borhaltigen Systemen auch die Stabilität dieser Systeme hinsichtlich ihrer inhärenten Reaktivität gegenüber Nukleophilen. Borafluorene sind von Natur aus stärkere Akzeptoren als ihre nicht benzannulierten Triarylboran-Derivate. In frühere Studien wurde bereits die Wirkung trifluormethylierter Aryle als exo-Aryl-Einheiten in Borfluororenen sowie die Auswirkung der Fluorierung auf das Rückgrat untersucht. Da letztere unter einer sehr geringen Stabilität leiden, wurden Systeme mit Trifluoromethylgruppen sowohl auf dem exo-Aromaten- als auch auf dem Borafluoren-Gerüst entwickelt, um sowohl die Stabilität als auch die Akzeptorstärke zu maximieren. Es wurden drei verschiedene perfluoralkylierte Borfluorene hergestellt und ihre elektronischen und photophysikalischen Eigenschaften untersucht. Die Systeme haben vier Trifluoromethylgruppen am Borafluoren-Gerüst sowie zwei Trifluoromethylgruppen an den ortho-Positionen ihrer exo-Aromaten. Sie unterscheiden sich in Bezug auf die para-Substituenten an ihren exo-Aromaten, die jeweils ein Proton (FXylFBf), eine Trifluormethylgruppe (FMesFBf) oder eine Dimethylaminogruppe (p NMe2 FXylFBf) sind. Des Weiteren wurde ein Acetonitril Addukt von FMesFBf isoliert und charakterisiert. Alle Derivate weisen außergewöhnlich niedrige Reduktionspotenziale auf, die mit denen von Perylendiimiden vergleichbar sind. Das elektronenärmste Derivat FMesFBf wurde ebenfalls chemisch reduziert und das korrespondierende radikalische Anion isoliert und charakterisiert. Eigenschaften aller Verbindungen untersucht. Alle Verbindungen weisen schwach erlaubte niederenergetischste Absorptionsmaxima, sowie sehr lange Fluoreszenzlebensdauern von ca. 250 ns bis zu 1,6 μs auf; die zugrunde liegenden Mechanismen, unterscheiden sich jedoch. Das donorsubstituierte Derivat p-NMe2-FXylFBf zeigt thermisch aktivierte verzögerte Fluoreszenz aus einem Ladungstransfer-(CT-)Zustand, während die Borafluorene FMesFBf und FXylFBf aufgrund ihrer Symmetrie und niedriger Übergangsdipolmomente nur schwach erlaubte lokal angeregte (LE-)Übergänge aufweisen, wie aus DFT- und TD-DFT-Berechnungen hervorgeht.   Kapitel 3 Konjugierte Dendrimere finden breite Anwendung in verschiedenen Bereichen, wie z.B. als Ladungstransport/-speicher- oder Emittermaterialien in organischen Solarzellen oder OLEDs. Bisherige Studien über borhaltige konjugierte Dendrimere sind rar gesät und verwenden meist einen konvergenten Syntheseansatz, dem ein einfacher, allgemein anwendbarer synthetischer Zugang fehlt. Ein neuer divergenter Ansatz wurde entwickelt und konjugierte Triarylboran-Dendrimere wurden bis einschließlich zur zweiten Generation synthetisiert. Die Synthesestrategie besteht aus drei Schritten: 1) Funktionalisierung durch Iridium-katalysierte C-H-Borylierung; 2) Aktivierung durch Fluorierung des erzeugten Boronatesters mit K[HF2] oder [N(nBu)4][HF2]; und 3) Expansion durch Reaktion der Trifluoroboratsalze mit Aryl-Grignard-Reagenzien. Das Konzept erwies sich auch auf einen konvergenten Ansatz übertragbar. Bis auf eine Ausnahme weisen alle konjugierten Boran-Dendrimere mehrere, isolierte und reversible Reduktionsprozesse auf, was sie zu potenziell interessanten Materialien für die Anwendung in molekularen Akkumulatoren macht. Basierend auf ihren photophysikalischen Eigenschaften zeigen die Dendrimere der 1. Generation eine gute Konjugation über das gesamte System. Bei der Erweiterung der Systeme zur zweiten Generation nimmt die Konjugation nicht weiter zu. Allerdings steigen die molaren Extinktionskoeffizienten linear mit der Anzahl der Triarylboran-Untereinheiten, was auf eine Möglichkeit für die Anwendung als photonische Antennen hindeutet.   Kapitel 4 Es wurde eine überraschend hohe, elektronisch gesteuerte Regioselektivität für die Iridium-katalysierte C-H-Borylierung mit [Ir(COD)OMe]2 (COD = 1,5-Cyclooctadien) als präkatalytische Spezies, Bis(pinacolato)diboran (B2pin2) als Borquelle und 4,4'-Di-tert-butyl-2,2'-bipyridin (dtbpy) als Ligand von D-π-A-Systemen mit Diphenylamin (1) oder Carbazolyl (Cbz-π (1)) als Donoren, Bis(2,6-bis(trifluoromethyl)phenyl)boryl (B(FXyl)2) als Akzeptor und 1,4-Phenylen als π-Brücke beobachtet. Unter diesen Bedingungen wurde die Borylierung nur an den sterisch am wenigsten gehinderten para-Positionen der Akzeptorgruppen beobachtet. Da Boronatester vielseitige Bausteine für die organische Synthese sind (C-C-Kupplung, funktionelle Gruppentransformationen), stellt die C–H-Borylierung eine einfache, potentielle Methode zur Funktionalisierung dar, mit der elektronische oder andere Eigenschaften von D-π-A-Systemen für spezifische Anwendungen fein abgestimmt werden können. Die photophysikalischen und elektrochemischen Eigenschaften der borylierten (1-(Bpin)2) und unborylierten (1) diphenylaminosubstituierten D-π-A-Systeme wurden untersucht. Interessanterweise weist das borylierte Derivat eine Koordination von THF an die Boronatester-Einheiten auf, was die photophysikalischen Eigenschaften beeinflusst und die Nicht-Unschuld der Boronatester veranschaulicht.

Chapter 1 N-Heterocyclic olefins (NHOs), relatives of N-heterocyclic carbenes (NHCs), exhibit high nucleophilicity and soft Lewis basic character. To investigate their π-electron donating ability, NHOs were attached to triarylborane π-acceptors (A) giving donor(D)-π-A compounds 1-3. In addition, an enamine π-donor analogue (4) was synthesized for comparison. UV-visible absorption studies show a larger red shift for the NHO-containing boranes than for the enamine analogue, a relative of a CAAC. The red shifted absorption of NHO-containing boranes indicate smaller energy gaps of NHO-containing boranes than CAAC-containing boranes. Solvent-dependent emission studies indicate that 1-4 have moderate intramolecular charge transfer (ICT) behavior. Electrochemical investigations reveal that the NHO-containing boranes have extremely low reversible oxidation potentials (e.g., for 3, E1/2ox = –0.40 V vs. Fc/Fc+ in THF) which indicate the electron rich property of NHOs. Furthermore, TD-DFT calculations were carried out on these four D-π-A boranes. The results show that the LUMOs of 1-4 only show a small difference, but the HOMOs of 1-3 are much more destabilized than that of the enamine-containing 4, which is in agreement with the electrochemical investigations and confirms the stronger donating ability of NHOs. Chapter 2 Since the beginning of this century, the chemistry of (hetero)arene-fused boroles has attracted increasing interest. (Hetero)arene-fused boroles exhibit strong Lewis acidity, distinct fluorescence properties, strong electron accepting abilities, etc. However, their chemistry been only very briefly reviewed either as part of reviews on “free” boroles or on boron-doped polycyclic aromatic hydrocarbons (PAHs). In this chapter, we addressed the chemistry of (hetero)arene-fused boroles from fundamentals to their widely varying applications. It includes: 1) Synthetic methodology  Both historical and recently developed strategies for the synthesis of fused boroles. 2) Stabilities  A comparison of different kinetic protection strategies. 3) 9-Borafluorenes with a fluorinated backbone  Application as Lewis acids, forming ion pairs with Cp2Zr(CH3)2 and applied as activators for polymerization, activators of H2, and other related applications. 4) Donor-acceptor 9-borafluorenes  Applications as F– “turn on” sensors, potential applications as electron accepting units for organic (opto)electronics, bipolar transporting materials, TADF materials, and different functionalization strategies. 5) Heteroarene-fused boroles  Enhanced antiaromaticity, unique coordination mode and their interesting properties. 6) Intramolecular dative bonding in 9-borafluorenes  Bond-cleavage-induced intramolecular charge transfer (BICT), BICT-induced large Stoke shifts and dual emissions, application as a ratiometric sensor. 7) 9-Borafluorene-based main chain polymers  Application in polymer chemistry and their distinct properties, e.g., as a sensor for gaseous NH3. 8) Electrochemistry  A comparison of electron-accepting ability of different functionalized fused boroles through electrochemical studies. 9) Chemical reduction of fused boroles  Stable radical anions and dianions of fused boroles and their properties. 10) Three-coordinate borafluorenium cations  Cationic 9-borafluorenes and their interesting properties, e.g., in THF, reversible thermal colour switching properties. Finally, a conclusion and outlook regarding the chemistry, properties and applications, and suggestions for areas which require further study was provided.   Chapter 3 Interested in fusing electron-poor arene onto boroles, two electron-poor phenylpyridyl-fused boroles, [TipPBB1]4 and TipPBB2 were prepared. [TipPBB1]4 is a white solid adopting a unique coordination mode, which forming a tetramer with a cavity in both the solid state and solution (1H DOSY). The boron center of TipPBB2 is 4-coordinate in the solid state, evidenced by a solid-state 11B{1H} RSHE/MAS NMR study, but the system dissociates in solution, leading to 3-coordinate borole species. [TipPBB1]4 exhibits two reduction processes which are attributed to the phenylpyridyl cores. TipPBB2 also exhibits two reduction processes with the first half-reduction potential of E1/2red = –1.94 V. The electron accepting ability of TipPBB2 is largely enhanced and comparable to that of FMesBf. This enhanced electron accepting ability is attributed to the electron withdrawing property of the pyridyl group. TipPBB2 exhibits concentration- and temperature-dependent dual fluorescence in solution. With the temperature is lowered, the emission intensity decreases (Figure 6.4, left). We suggested that the dual fluorescence is caused by an equilibrium between 3-coordinate TipPBB2 and a weak intermolecular adduct of TipPBB2 via a B–N bond. This hypothesis was further supported by lifetime measurements at different concentrations, low temperature excitation spectra low temperature 1H NMR spectra and lifetime measurements upon addition of DMAP to a solution of TipPBB2 to simulate the 4-coordiante TipPBB2 species. Interestingly, the ratio of the relative percentages of the two lifetimes shows a linear relationship with temperature; thus, TipPBB2 could serve as a fluorescent thermometer. Furthermore, theoretical studies were carried out on TipPBB2, and two models, ((BMe3)TipPBB1(NMe3) and (BMe3)TipPBB2(NMe3)), which utilize a BMe3 group as the Lewis acid coordinated to pyridine and an NMe3 group as the Lewis base coordinated to the boron center of the borole, were used to simulate the [TipPBB1]4 and intermolecular 4-coordinate TipPBB2, respectively. Theoretical studies indicate that the HOMO of TipPBB2 is located at the Tip group, which is in contrast to its borafluorene derivatives for which the HOMOs are located on the borafluorene cores. Chapter 4 Two derivatives of phenylpyridyl-fused boroles were prepared via functionalization of the pyridyl groups in two different directions, namely an electron-rich dihydropyridine moiety (compound 10) and an electron-deficient N-methylpyridinium cation (compound 11). Both compounds were fully characterized. The 11B NMR signal of compound 10 was observed at 58.8 ppm in CDCl3, which suggests strong conjugation between the boron atom and dihydropyridine moiety. Compound 11 shows a reversible coordination to THF which was confirmed by NMR studies. Compared to other 2,4,6-triisopropylphenyl protected 9-borafluorenes which only coordinate to CH3CN or DMF, the coordination of the weaker and bulkier THF to compound 11 indicates an extremely electron-deficient boron center in compound 11. The electron-rich property of the dihydropyridine moiety of compound 10 was confirmed by its oxidation potential (Epc = +0.37 V). Due to the strong conjugation of the dihydropyridine moiety with the boron atom, the reduction potential of compound 10 shifts cathodically and is more negative than –2.5 V. Compound 11 exhibits three reduction processes with the first reversible reduction potential at Ered1/2 = –1.23 V, which is significantly anodically shifted compared to that of its precursor (TipPBB2) or its framework 1-methyl-2-phenylpyridin-1-ium triflate (12). This significantly anodically shifted reduction potential confirms an extremely electron-deficient property of compound 11. Photophysical studies indicate that the lowest energy transition of compound 10 is more likely a locally-excited (LE) transition and compound 11 exhibits a polarized ground state. Furthermore, we performed theoretical studies for both compounds. The electron cloud distribution of the HOMO of compound 10 supports the strong conjugation between the boron atom and the dihydropyridine moiety in the ground state. An extremely low LUMO energy was determined by theoretical studies which confirmed the extremely electron-deficient property of compound 11.   Chapter 5 Inspired by the enhancement of electron accepting ability with increasing numbers of electron withdrawing groups at boron, we tried to study the properties of a bis(pyridyl)arylboranes. In our attempt to synthesize a bis(pyridyl)arylborane, we obtained a bis(2-pyridyl)methoxyborate Li+ complex which is as a dimer both in solution and the solid state. In the solid state, compound [16]2 is a dimer containing two bis(2-pyridyl)methoxyborate which are linked by two lithium cations. Each lithium cation coordinates to one methoxy group and two pyridyl groups, one from each of the two bis(2-pyridyl)methoxyborate anions. The parameters of [16]2 were compared with other bis(2-pyridyl)methoxyborate stabilized Pt(IV) complex, bis(2-pyridyl)hydroxylborate stabilized Ru(II) complex and the dimer of EtAl(OMe)(2-pyridyl)2Li. To confirm the coordination mode in solution, 1H DOSY spectroscopy was carried out in CD2Cl2. The van der Waals radius obtained by 1H DOSY nicely matches with the result from the solid state and thus proves the dimer of 16 is persistent in solution. Finally, different Lewis acids (e.g., TMSCl, BF3•Et2O, AlCl3, HCl) were used to attempt to detach the methoxy group of [16]2. However, we observed either decomposition or selective cleavage of the Tip group, or no reaction at all, rather than cleavage of the methoxy group from boron. / 1 Kapitel 1 N-Heterocyclische Olefine (NHOs) sind Verwandte der N-heterocyclischen Carbene (NHCs) und weisen eine hohe Nukleophilie sowie einen weichen Lewis-Grundcharakter auf. Um ihre Fähigkeit als π-Elektronendonor zu untersuchen, wurden diese NHOs an π-Triarylboran-Akzeptoren (A) gebunden, wodurch die Donor(D)-π-A-Verbindungen 1-3 erhalten wurden. Zusätzlich wurde zum Vergleich das Enamin π-Donoranalogon (4) synthetisiert. Studien zur UV/Vis-Absorption zeigen für die NHO-haltigen Borane eine stärkere Rotverschiebung als für das Enamin-Analogon, welches ein Verwandter von CAACs ist. Die rotverschobene Absorption der NHO-haltigen Borane weist auf kleinere Energielücken bei den NHO-haltigen Boranen als bei den CAAC-haltigen Boranen hin. Des Weiteren zeigen Lösungsmittel-abhängige Emissionsstudien, dass die Verbindungen 1-4 ein moderates intramolekulares Ladungstransfer(ICT)-Verhalten aufweisen. Elektrochemische Untersuchungen zeigen, dass die NHO-haltigen Borane extrem niedrige reversible Oxidationspotentiale aufweisen (z.B. für 3, E1/2ox = –0,40 V vs. Fc/Fc+ in THF), was auf die elektronenreiche Eigenschaft der NHOs hinweist. Darüber hinaus wurden TD-DFT-Berechnungen für diese vier D-π-A-Borane durchgeführt. Die Ergebnisse zeigen, dass die jeweiligen LUMOs von 1-4 nur einen geringen Unterschied zueinander aufweisen, die HOMOs von 1-3 jedoch viel stärker destabilisiert sind als die des enaminhaltigen 4, was mit den elektrochemischen Untersuchungen übereinstimmt und die stärkere Donorfähigkeit der NHOs bestätigt. 2 Kapitel 2 Seit Beginn dieses Jahrhunderts hat die Chemie von (Hetero)aren-kondensierten Borolen zunehmendes Interesse geweckt. (Hetero)aren-kondensierte Borole weisen eine starke Lewis-Acidität, ausgeprägte Fluoreszenzeigenschaften, starke Elektronenakzeptor-fähigkeiten, etc. auf. Ihre Chemie wurde jedoch bislang nur wenig untersucht und es gibt kaum Übersichten zu ihren Eigenschaften, entweder als Teil von Übersichtsarbeiten über "freie" Borole oder über bordotierte polyzyklische aromatische Kohlenwasserstoffe (PAK). In diesem Kapitel wird die Chemie von (Hetero)aren-kondensierten Borolen von den Grundlagen bis zu ihren sehr unterschiedlichen Anwendungen behandelt. Es umfasst: 1) Synthetische Methoden  Sowohl historische als auch kürzlich entwickelte Strategien für die Synthese von kondensierten Borolen. 2) Stabilitäten  Ein Vergleich verschiedener kinetischer Schutzstrategien. 3) 9-Borafluorene mit fluoriertem Rückgrat  Anwendung als Lewis-Säure, Bildung von Ionenpaaren mit Cp2Zr(CH3)2 und Anwendung als Aktivatoren für die Polymerisation, Aktivatoren von H2 und andere verwandte Anwendungen. 4) Donor-Akzeptor 9-Borafluorene  mögliche Anwendungen als F– "Einschalt"-Sensoren, als elektronenakzeptierende Einheit für die organische (Opto-)Elektronik, bipolare Transportmaterialien, TADF-Materialien und verschiedene Funktionalisierungsstrategien. 5) Heteroaren-kondensierte Borole  Gesteigerte Antiaromatizität, einzigartiger Koordinationsmodus und interessante Eigenschaften. 6) Intramolekulare dative Bindung in 9-Borafluorenen  Bindungsbruch-induzierter intramolekularer Ladungstransfer (BICT), BICT-induzierte große Stokes-Verschiebungen und duale Emissionen, Anwendung als ratiometrischer Sensor. 7) 9-Borafluoren-basierte Hauptkettenpolymere  Anwendung in der Polymerchemie und deren charakteristische Eigenschaften, z.B. als Sensoren für gasförmiges NH3. 8) Elektrochemie  Ein Vergleich der Elektronenakzeptorfähigkeit unterschiedlicher funktionalisierter kondensierter Borole durch elektrochemische Untersuchungen. 9) Chemische Reduktion von kondensierten Borolen  Stabile Radikalanionen und Dianionen von kondensierten Borolen und deren Eigenschaften. 10) Dreifach koordinierte Borafluorenium-Kationen  Kationische 9-Borafluorene und ihre spannenden Eigenschaften, wie z.B. die reversible thermische Schaltbarkeit durch Farbe in THF. Am Ende des Kapitels werden Schlussfolgerungen gezogen und ein Ausblick zur weiteren Chemie, etwaigen Eigenschaften sowie möglichen Anwendungen gegeben. Ferner werden Vorschläge zu Feldern gemacht, die weitere Untersuchungen bedürfen. 3 Kapitel 3 Um elektronenarme Arene mit Borolen zu kondensieren, wurden zwei elektronenarme Phenylpyridyl-kondensierte Borole, [TipPBB1]4 und TipPBB2, hergestellt. [TipPBB1]4 ist ein weißer Feststoff, der einen einzigartigen Koordinationsmodus aufweist. Sowohl im Festkörper als auch in Lösung (1H DOSY) liegt ein Tetramer mit einem Hohlraum vor. Das Borzentrum von TipPBB2 ist im Festkörper 4-fach koordiniert, was durch ein Festkörper 11B{1H} nachgewiesen wurde. RSHE/MAS-NMR-Studien zeigten aber, dass das System in Lösung dissoziiert, was zu einer 3-fach koordinierten-Borolspezies führt. [TipPBB1]4 zeigt zwei Reduktionsprozesse, die den Phenylpyridylkernen zugeschrieben werden. TipPBB2 zeigt ebenfalls zwei Reduktionsprozesse mit dem ersten Halb- Reduktionspotential von E1/2red. = –1,94 V. Die Elektronenakzeptorfähigkeit von TipPBB2 ist somit weitgehend verbessert und mit der von FMesBf vergleichbar. Diese verbesserte Elektronenakzeptorfähigkeit ist auf den elektronenziehenden Effekt der Pyridylgruppe zurückzuführen. TipPBB2 zeigt konzentrations- und temperaturabhängige duale Fluoreszenz in Lösung. Mit sinkender Temperatur nimmt die Emissionsintensität ab. Es liegt die Vermutung nahe, dass die duale Fluoreszenz durch ein Gleichgewicht zwischen 3-fach koordinierten-TipPBB2 und einem schwachen intermolekularen Addukt von TipPBB2 über eine B–N-Bindung verursacht wird. Diese Hypothese wurde durch Lebenszeitmessungen bei verschiedenen Konzentrationen, Niedrigtemperatur-Anregungsspektren, Niedrigtemperatur-1H-NMR-Spektren und Lebenszeitmessungen nach Zugabe von DMAP zu einer Lösung von TipPBB2 zur Simulation der 4-fach koordinierten-TipPBB2-Spezies weiter untermauert. Interessanterweise zeigt das Verhältnis der relativen Prozentsätze der beiden Lebenszeiten eine lineare Beziehung mit der Temperatur; daher könnte TipPBB2 als Fluoreszenzthermometer dienen. Darüber hinaus wurden theoretische Studien zu TipPBB2 durchgeführt und zwei Modellverbindungen ((BMe3)TipPBB1(NMe3) und (BMe3)TipPBB2(NMe3)) wurden untersucht, um [TipPBB1]4 bzw. das intermolekular-4-fach koordinierte TipPBB2 zu simulieren. Die BMe3-Gruppe koordiniert als Lewis-Säure an Pyridin und die NMe3-Gruppe als Lewis-Base an das Borzentrum des Borols. Die theoretischen Studien weisen darauf hin, dass das HOMO von TipPBB2 an der Tip-Gruppe lokalisiert ist, was im Gegensatz zu den entsprechenden Borafluoren-Derivaten steht, bei denen sich die HOMOs auf den Borafluoren-Kernen befinden. 4 Kapitel 4 Zwei Derivate von Phenylpyridyl-kondensierten Borolen wurden durch Funktionalisierung der Pyridylgruppe an zwei unterschiedlichen Positionen hergestellt, zum einen eine elektronenreiche Dihydropyridin-Einheit (Verbindung 10) und zum anderen ein elektronenarmes N-Methylpyridinium-Kation (Verbindung 11). Beide Verbindungen wurden vollständig charakterisiert. Das 11B-NMR-Signal von Verbindung 10 wurde bei 58,8 ppm in CDCl3 beobachtet, was auf eine starke Konjugation zwischen dem Boratom und der Dihydropyridin-Einheit schließen lässt. Verbindung 11 zeigt eine reversible Koordination zu THF, was durch NMR-Studien bestätigt wurde. Im Vergleich zu anderen 2,4,6-Triisopropylphenyl-geschützten 9-Borafluorenen, die nur an CH3CN oder DMF koordinieren, weist die Koordination des schwächeren und voluminöseren THF zu Verbindung 11 auf ein extrem elektronenarmes Borzentrum in Verbindung 11 hin. Der Elektronenreichtum der Dihydropyridin-Einheit von Verbindung 10 wurde durch sein Oxidationspotential (Epc = +0,37 V) bestätigt. Aufgrund der starken Konjugation des Dihydropyridinteils mit dem Boratom verschiebt sich das Reduktionspotential von Verbindung 10 kathodisch und ist negativer als –2,5 V. Verbindung 11 zeigt drei Reduktionsprozesse mit dem ersten reversiblen Reduktionspotential bei Ered1/2 = –1,23 V, das im Vergleich zu dem der Vorstufe (TipPBB2) oder ihres Gerüstes 1-Methyl-2-phenylpyridin-1-ium-Triflat (12) signifikant anodisch verschoben ist. Dieses signifikant anodisch verschobene Reduktionspotential bestätigt das Elektronendefizit von Verbindung 11. Photophysikalische Studien zeigen, dass der niedrigste Energieübergang von Verbindung 10 eher ein lokal angeregter (LE) Übergang ist und Verbindung 11 einen polarisierten Grundzustand aufweist. Darüber hinaus wurden für beide Verbindungen theoretische Studien durchgeführt. Die Elektronenverteilung des HOMO von Verbindung 10 belegt die starke Konjugation zwischen dem Boratom und der Dihydropyridin-Einheit im Grundzustand. Eine sehr niedrige LUMO-Energie wurde durch theoretische Studien ermittelt, die das Elektronendefizit von Verbindung 11 bestätigt. 5 Kapitel 5 Inspiriert durch die zunehmende Elektronenakzeptorfähigkeit mit wachsender Anzahl elektronenziehender Gruppen am Boratom versuchten wir, die Eigenschaften eines Bis(pyridyl)arylborans zu untersuchen. Bei unserem Versuch, ein Bis(pyridyl)arylboran zu synthetisieren, erhielten wir jedoch einen Bis(2-pyridyl)methoxyborat-Li+-Komplex, der als Dimer sowohl in Lösung als auch im festen Zustand vorliegt. Im Festkörper ist die Verbindung [16]2 ein Dimer, das zwei Bis(2-pyridyl)methoxyborat-Einheiten enthält welche durch zwei Lithiumkationen verbunden sind. Jedes Lithiumkation koordiniert an eine Methoxygruppe und an zwei Pyridylgruppen, jeweils eine von jedem der beiden Bis(2-pyridyl)methoxyborat-Anionen. Die Parameter von [16]2 wurden mit anderen Bis(2-pyridyl)methoxyborat-stabilisierten Pt(IV)-Komplexen, Bis(2-pyridyl)hydroxylborat-stabilisierten Ru(II)-Komplexen und dem Dimer von EtAl(OMe)(2-pyridyl)2Li verglichen. Um den Koordinationsmodus in Lösung zu bestätigen, wurde eine 1H-DOSY-Studie in CD2Cl2 durchgeführt. Der aus den Daten ermittelte van-der-Waals-Radius stimmt gut mit dem Ergebnis aus den Festkörperuntersuchungen überein und beweist somit, dass das Dimer von 16 in Lösung persistent ist. Schließlich wurde mit verschiedenen Lewis-Säuren (z.B. TMSCl, BF3•Et2O, AlCl3, HCl) versucht, die Methoxygruppe von [16]2 abzuspalten. Wir beobachteten jedoch entweder eine Zersetzung oder selektive Abspaltung der Tip-Gruppe oder gar keine Reaktion und nicht die Abspaltung der Methoxy-Gruppe von Bor.

This dissertation describes the synthesis of an unsymmetrically-substituted triarylborane. This term describes a three-coordinate boron atom that is bound to three different aromatic systems, namely 2,6-dimethylphenyl, mesityl, and 4-(N,N-dimethylamino)-2,6-dimethylphenyl. It is also demonstrated that the amine functionality can be converted with methyl triflate into an ammonium moiety. The investigation of photophysical and electrochemical properties of this compound in comparison with the non-aminated and di-aminated analogues of the triarylborane is described besides other investigations of e. g. singlet oxygen sensitization, rotational barriers, and fundamental DFT calculations. Based on these investigations, selectively mono-, bis- and tris-dimethylamino- and trimethylammonium-substituted bis-triarylborane bithiophene chromophores were synthesized and their photophysical, and electrochemical properties were investigated together with the water solubility and singlet oxygen sensitizing efficiency of the cationic compounds Cat1+, Cat2+, Cat(i)2+, and Cat3+. Comparing these properties with the results obtained for the mono-triarylboranes reveals a large influence of the bridging unit on the investigated properties of the bis-triarylboranes. In addition, the interaction of the cationic bis-triarylboranes with different polynucleotides were investigated in buffered solutions as well as the ability of these selectively charged compounds to enter and localize within organelles of human lung carcinoma and normal lung cells. All these investigations demonstrate that the number of charges and their distribution influences the interactions and staining properties as well as most of the other properties investigated. In addition, preliminary investigations on H2O2-cleavable boronate esters in the presence of stochiometric amounts of H2O2 are described for three different aryl boronate esters. / In dieser Doktorarbeit wird die Synthese eines unsymmetrisch subsitutierten Triarylborans beschrieben. Dieser Ausdruck beschreibt ein dreifach koordiniertes Boratom, das an drei unterschiedliche Aromaten, hier 2,6-Dimethylphenyl, Mesityl, and 4-(N,N-Dimethylamino)-2,6-dimethylphenyl, gebunden ist. Es wird gezeigt, dass die Aminofunktionalität durch Methyltriflat in eine Amminoeinheit überführt werden kann. Die Untersuchung der photophysikalischen und elektrochemischen Eigenschaften dieser Verbindung im Vergleich zu den nicht-aminierten und di-aminierten Analoga des Triarylborans ist beschrieben ebenso wie beispielsweise die Untersuchungen der Bildung von Singulet Sauerstoff, der Rotationsbarrieren und fundamentale DFT Berechnungen. Basierend auf diesen Untersuchungen wurden genau einfach, zweifach und dreifach Dimethylamino- und Trimethylammonium-substituierte Chromophore hergestellt und deren photophysikalische und elektrochemische Eigenschaften untersucht, zusammen mit der Wasserlöslichkeit und der Bildung von Singulet Sauerstoff der kationischen Verbindungen Cat1+, Cat2+, Cat(i)2+ und Cat3+. Der Vergleich dieser Eigenschaften mit den Ergebnissen der mono-Triarylborane zeigt den großen Einfluss der Brücke auf die untersuchten Eigenschaften der bis-Triarylborane. Zusätzlich wurden die Wechselwirkungen der kationischen bis-Triarlyborane mit unterschiedlichen Polynukeotiden in Pufferlösungen zusammen mit deren Fähigkeit in Lungenkrebs- und Lungenzellen zu gelangen und sich in bestimmten Organellen darin anzulagern. Diese Untersuchungen zeigen, dass die Anzahl und Verteilung der Ladungen nicht nur die Wechselwirkungen und intrazelluläre Lokalisation beeinflussen, sondern auch fast alle übrigen untersuchten Eigenschaften. Zusätzlich sind erste Untersuchungen von drei H2O2-spaltbaren Borsäureestern in der Gegenwart von stöchiometrischen Mengen Wasserstoffperoxid gezeigt.

The 1st chapter provides a detailed review of the development of synthetic approaches to triarylboranes from their first report nearly 135 years ago to the present. In the 2nd chapter, a novel and convenient methodology is reported for the one-pot synthesis of sterically-congested triarylboranes, using bench-stable aryltrifluoroborates as the boron source. The new procedure gives access to symmetrically- and unsymmetrically-substituted triarylboranes. The borylated triarylboranes are suggested as building blocks for the design of functional materials. In the 3rd chapter, four luminescent tetracationic bis-triarylborane DNA and RNA sensors that show high binding affinities, in several cases even in the nM range, are investigated. The molecular structures of two of the neutral precursors reveal some structural flexibility for these compounds in the solid state. The compounds were found to be highly emissive even in water and DNA and RNA binding affinities were found to be dependent on linker length and flexibility. Strong SERS responses for three of the four compounds demonstrate the importance of triple bonds for strong Raman activity in molecules of this compound class. In chapter 4, the compound class of water-soluble tetracationic bis-triarylborane chromophores is extended by EDOT-linked compounds and those are compared to their thiophene-containing analogs. Absorption and emission are significantly red-shifted in these compounds, compared to their thiophene-containing analogs and, due to a large Stokes shift, one of the reported compounds exhibits the most bathochromically shifted emission, observable well into the near infrared region, of all tetracationic water-soluble bis-triarylborane chromophores reported to date. Long-lived excited states, completely quenched by oxygen, were observed for the water-stable compounds of this study via transient absorption spectroscopy and a quantum yield for singlet oxygen formation of 0.6 was determined for one of them. / Das erste Kapitel gibt einen detaillierten Überblick über die Entwicklung verschiedener Synthesemöglichkeiten von Triarylboranen seit ihrer erstmaligen Erwähnung vor rund 135 Jahren bis heute. In Kapitel 2 wurde eine neuartige und praktische Methode für die Eintopfsynthese von sterisch stabilisierten Triarylboranen unter Verwendung von luftstabilen Aryltrifluorboraten als Borquelle beschrieben. Das neue Verfahren ermöglicht den Zugang zu symmetrisch und unsymmetrisch substituierten Triarylboranen, die bei der Konstruktion borhaltiger Funktionsmaterialien verwendet werden könnten. Im dritten Kapitel wurden tetrakationische Bis-Triarylborane bezüglich DNA- und RNA-Sensorik untersucht, wobei hohe Bindungsaffinitäten, wurden. Die Molekülstrukturen von zwei neutralen Vorstufenverbindungen deuten auf eine gewisse Flexibilität für diese Verbindungen im Festkörper hin. Die Verbindungen erwiesen sich selbst in Wasser als stark emittierend und die DNA und RNA Bindungsaffinitäten waren abhängig von Länge und Flexibilität des Linkers. Starke SERS-Signale für drei der vier Verbindungen, zeigen die Bedeutung von Dreifachbindungen für eine starke Raman-Aktivität in Molekülen dieser Verbindungsklasse. In Kapitel 4 dieser Arbeit wurde die Verbindungsklasse wasserlöslicher tetrakationischer Bis Triarylboran-Chromophore um EDOT-verbrückte Verbindungen erweitert und diese mit ihren literaturbekannten Thiophenanaloga verglichen. Absorption und Emission sind in diesen Verbindungen im Vergleich zu ihren Thiophen-haltigen Analoga rotverschoben und eine der Verbindungen zeigt die am weitesten rotverschobene, noch weit im nahen Infrarotbereich detektierbare, Emission aller bisher bekannten Verbindungen dieser Art. Für die wasserstabilen Verbindungen wurden mittels transienter Absorptionsspektroskopie langlebige Zustände beobachtet, die vollständig durch Sauerstoff gequencht werden und eine Quantenausbeute für die Singulett-Sauerstoffbildung von 0.6 wurde für eine der Verbindungen bestimmt.

The main thrust of this thesis is the development of new triarylborane containing luminescent molecules as well as utilizing triarylboron center as a receptor for the selective detection of biologically, environmentally and industrially important anions such as fluoride and cyanide in aqueous and non-aqueous solutions. The thesis contains nine chapters. The contents of each chapter are described below. Chapter 1 The first chapter is an introduction to the theme of the thesis and presents a general review on the techniques, theories and photochemistry relevant to the present work with emphasis on photochemistry of triarylboranes and their importance in the field of anion sensor chemistry. A review on various boron based luminophores is also presented. Chapter 2 The second chapter deals with the general experimental techniques and synthetic procedures utilized in this work. Chapter 3 This chapter deals with the synthesis of boryl-BODIPY dyads (1-8) in which triarylborane acts as anion receptor and BODIPY as a signalling unit. The absorption spectra of all boryl-BODIPY dyads shows similar pattern. However, the fluorescence spectra of 1, 2, 3, 6 and 7 shows dual emission bands whereas 4, 5 and 8 exhibit a single emission band. These interesting photophysical properties of boryl-BODIPYs (1-8) depends on the dihedral angle between two chromophores and partial energy transfer from donor (triarylborane) to acceptor (BODIPY) unit. The energy transfer efficiency of compounds 4, 5 and 8 is higher (close to 100%) compared to other series of boryl-BODIPYs (1-3, 6 and 7), due to the orthogonal arrangement of chromophores with high dihedral angles. To better understand photophysical properties and energy transfer process, anion binding studies were carried out since triarylborane acts as receptor for fluoride and cyanide ions. Anion binding studies of boryl-BODIPYs were (1-5) carried out in dichloromethane solutions and using tetrabutylammonium salt of fluoride/cyanide. All boryl-BODIPY dyads (1-5) were sensitive and selective sensor of fluoride, whereas the presence of only excess amounts (20 equv or more amounts) of cyanide made any changes in absorption and emission spectra. Other anions even above 100 eq were unable to cause any change. The quenching efficiency of compounds 4 and 5 was found to be more than that of other boryl-BODIPYs (1 and 3). The binding of fluoride with boryl-BODIPY (1-5) was entirely reversible; addition of BF3•Et2O to the fluoride adducts of compounds (1-5) regenerated the parent compounds. Chapter 4 In chapter 3, it was established that linear boryl-BODIPY dyads (1-8) show dual/single fluorescence bands depending on the dihedral angle between triarylborane and BODIPY unit. This Chapter describes the synthesis of three new “V” shaped boryl-BODIPY dyads (9, 10 and 11) their optical properties, Compound 9-11 are structurally similar differing only in the number of methyl substituents on the BODIPY moiety which were found to play major role in determining their optical behavior. The dyads show rare forms of multiple channel emission characteristics arising from different extents of electronic energy transfer (EET) processes between the two covalently linked fluorescent chromophores (triarylborane and BODIPY units). Owing to the presence of Lewis acidic triarylborane moiety, the dyads function as highly selective and sensitive fluoride sensors with vastly different response behavior. Upon binding of fluoride to the tricoordinate borane centre, dyad 9 shows gradual quenching of its BODIPY dominated emission due to the cessation of (borane to BODIPY) EET process. Dyad 10 shows ratiometric changes in its emission behavior upon addition of fluoride. Dyad 11 forms fluoride induced nanoaggregates which result in fast and effective quenching of its emission intensity upon addition of even small quantities of analyte (i.e. 0.1 equivalent of fluoride). When the solution is allowed to stand, disaggregation of the molecules results in partial recovery of the initial fluorescence bands. Thus, small structural alterations in these three structurally close dyads (9-11) result in exceptionally versatile and unique photophysical behavior and remarkably diverse responses towards a single analyte i.e. fluoride anion. Chapter 5 This chapter deals with intermolecular charge transfer (ICT) process in borane containing donor-acceptor triads and tetrads to realize colorimetric response for small anions such as fluoride and cyanide. Triad 12 and tetrad 13 incorporating –B(Mes)2, BDY (borondipyrromethene), and TPA (triphenylamine) were synthesized. Introduction of two dissimilar acceptors (triarylborane and BODIPY) on a single donor (TPA) resulted in two distinct ICT process (amine to borane and amine to BDY). The absorption and emission properties of new triad and tetrad are highly dependent on individual building units. The nature of electronic communication among the individual fluorophore units has been comprehensively investigated and compared with building units. Compounds 12 and 13 showed chromogenic and fluorogenic response towards small anions such as fluoride and cyanide. Chapter 6 In the previous chapter, it was demonstrated that although triphenylamine-triarylborane-BODIPY donor-acceptor conjugates show colorimetric response towards fluoride and cyanide. They could not distinguish these two interfering anions. To overcome the anion interference peripherally triarylborane decorated porphyrin (14) and its Zn(II) complex (15) were designed and synthesized and this forms the subject matter of this Chapter. Compound 15 contains two different Lewis acidic binding sites (Zn(II) and boron centre). Unlike all previously known triarylborane based sensors, the optical responses of 15 towards fluoride and cyanide are distinctively different thus enabling the discrimination of these two interfering anions. Metalloporphyrin 15 shows a multiple channel fluorogenic response towards fluoride and cyanide and also a selective visual colorimetric response towards cyanide. By comparison with model systems and from detailed photophysical studies on 14 and 15, it was concluded that the preferential binding of fluoride occurs at the peripheral borane moieties resulting in the cessation of the EET (electronic energy transfer) process from triarylborane to porphyrin core and with negligible negative cooperative effects. On the other hand, cyanide binding occurs at the Zn(II) core leading to drastic changes in its absorption behavior which can be followed by the naked eye. Such changes are not observed when the boryl substituent is absent (e.g. tetraphenyl-Zn(II)-porphyrin or TPP). The conjugates 14 and 15 showed reversible binding interaction towards CN and F and they are capable of extracting fluoride from aqueous media. Chapter 7 This Chapter deals with the design of a sensor which can detect fluoride colorimetrically in aqueous medium. Detecting fluoride in aqueous solution is an important area of current research owing to both positive and negative health and environmental effects associated with the fluoride ion. Although numerous fluoride sensors are reported, the colorimetric sensing (visual detection without the need of costly equipment and complicated analytical of fluoride at recommended levels 0.7 ppm) has not realized. Here we report the design, optical and fluoride sensing ability of two new water soluble Lewis acidic triarylborane-triarylamine conjugates 16 and 17 (containing one or two ammonium cations (-C6H4-NMe3). Compound 17 shows selective colorimetric response for aqueous inorganic fluoride at as low a level as 0.1 ppm Chapter 8 The synthesis and optical properties of four new triarylborane–dipyrromethane (TAB– DPM) conjugates (19a–d) containing dual binding sites (hydrogen bond donor and Lewis acid) have been reported. The new compounds exhibit a selective fluorogenic response towards the F− ion. The NMR titrations show that the fluoride ions bind to the TAB–DPM conjugates via the Lewis acidic triarylborane centre in preference to the hydrogen bond donor (dipyrromethane) units. Chapter 9 A new triarylborane-aza-BODIPY conjugate is reported (22). The conjugate molecule consists of two blue emissive dimesitylarylborane moiety and a NIR (near infra-red) emissive aza-BOIDPY core and shows panchromatic absorption spanning over ~300-800 nm region. The presence of two different fluorophore units in the conjugate leads to a broad dual-emissive feature covering a large part of visible and NIR region. DFT computational studies suggest limited electronic communication between the individual fluorophore units which may be responsible for the intriguing optical features of the conjugate molecule. Further, the broadband emissive conjugate can act as a selective sensor for fluoride anion as a result of fluorescence quenching response in both visible as well as in NIR spectral region.

Luminescent boron containing materials find numerous applications in modern technologies such as display/lighting, bio-imaging and sensing. Thus, investigations of structure-property relationships in organic luminescent compounds to understand their molecular and bulk properties are of fundamental importance. The main thrust of this thesis is the development of facile synthetic routes for boron containing novel polyads and study their structure-property correlations and to utilize this information to design functional materials with desired properties such as multiple emission, bio imaging, anion sensing and organic photo voltaic characteristics. This thesis contains seven chapters and the contents of each chapter are described below. Chapter 1 This chapter is a concise overview of the recent developments in the chemistry of boron based molecular systems such as triarylborane and BODIPYs. This chapter also highlights the basic nature of broad emissive materials. In addition, an advance in the frontier areas such as bio imaging is discussed in brief. Chapter 2 This chapter describes the structure and optical properties of a new triad (Borane-Bithiophene-BODIPY) 1. Triad 1 exhibits unprecedented tricolour emission when excited at borane centred high energy absorption band and also acts as a selective fluorescent and colorimetric sensor for fluoride ion with ratiometric response. The experimental results are supported by computational studies. Chapter 3 Two fluorescent compounds with similar absorption profiles and complementarily emissive properties can be regarded as the ideal couple for the generation of white-light. Two structurally close and complementarily fluorescent boron based molecular siblings 2 and 3 were prepared. The luminescence properties of individual triads were modulated to an extent to complement each other by controlling the intramolecular energy transfer in triads by fine-tuning the dihedral angle between fluorophores in 2 and 3. A binary mixture of 2 and 3 emitted white-light. Chapter 4 This chapter deals with a straight forward strategy for the generation of white-light emission in aqueous media. Using a blue-emissive AIE-active (aggregation-induced emission) 1, 8-naphthalimide- based sensitizer and a boron-dipyrromethene based red emitter as a dopant, water dispersible nanostructures with tunable emission features are produced. The white-light emissive (WL) nano-aggregates are stable at neutral pH and have been elegantly utilized for four-colour cell imaging (including near- infrared imaging). Chapter 5 This chapter describes the design and development of a NIR emitting triarylborane decorated styryl-BODIPY (4) via a facile synthetic route. Incorporation of TAB entities results in a significantly red shifted broad emission in 4 (compared to compound M3 which is devoid of TAB unit). The near coplanar orientation of Ar3B planes and BODIPY core results in a highly efficient (TAB to BODIPY) EET process in 4. Conjugate 4 acts as a highly selective and sensitive fluoride sensor with naked eye visual response as well as ratiometric fluorescent response. The dual emission in fluoride bound 4 possibly results from the restricted partial TAB to BODIPY energy transfer. Chapter 6 This chapter describes how the energy of transitions of the broad emissive molecular triads can be fine-tuned by judiciously changing the spacer oligothiophene length. A series of triarylborane and BODIPY conjugates (TAB-π-BODIPY) has been designed, and synthesized by a combined strategy of changing the connection mode between the two units, extending the conjugation size by introducing terthiophene, quaterthiophene, and pentathiophene units. The electrochemical and photophysical behavior of these conjugates were investigated. The experimental findings were rationalized by density functional theory calculations. Chapter 7 This chapter describes design and development of boron based novel electron acceptor BDY for the bulk-heterojunction solar cell. The electron mobility values of BDY was found to be of the order of standard PCBM. Bulk-heterojunction was fabricated using BDY as the electron acceptor layer. The power conversion efficiency of the newly developed solar cells with BDY as electron acceptor is much higher than the value obtained for standard cells with PCBM as the electron acceptor.

The main thrust of this thesis is the development of facile synthetic routes for simple boryl anilines and study their structure-property correlations in both solid and solution states and to utilize this information to design functional materials with desired properties such as aggregation induced emission, mechanofluorochromism, and thiol sensors. This thesis contains eight chapters and the contents of each chapter are described below. Chapter 1 The first chapter is an introduction to the theme of the thesis and presents a general review on the present work with emphasis on photophysics of triarylboron based donor-acceptor systems and their applications in various fields. In addition, advances in boron chemistry in the new frontier areas such as aggregation induced emission and mechanochromism are discussed in brief. Chapter 2 The second chapter deals with the general experimental techniques and synthetic procedures utilized in this work. Chapter 3 This chapter describes the rational design and synthesis of triarylborane bearing Unsubstituted amines, namely borylanilines (3.1-3.5). Compounds 3.1-3.4have similar donor and acceptor centres but differ their molecular conformations and also differ in the relative positions of amine moiety (para and meta). Compounds 3.1-3.4 contain one amine group while 3.5 contains two amine moieties. These compounds exhibit fascinating electrostatic intermolecular interactions, N −H- - -π in the crystal structure of 3.1, 3.2 and 3.4 and N −H--N interactions in crystal structure of 3.5. The solution state optical properties of 3.1-3.5 are typical of donor-acceptor (D-A) systems. Interestingly, compounds 3.3 and 3.5 showed unprecedented mechanochromic luminescent properties. Upon grinding, compound 3.3 showed color changes from blue to cyan blue and 3.5 showed intriguing color changes from blue to green and these color changes were found to be reversible. Single crystal X-ray diffraction analysis of 3.5BP (blue emission color crystal) and 3.5GP (green emission color crystal) clearly show that the color changes are due to the difference in their solid state packing. Chapter 4 In chapter 4, the design and facile synthesis of boron based donor-acceptor (D-A) systems such as borylanilines 4.4-4.9 (D= -NH2 for 4.4-4.6 and -NMe2 for compounds 4.7-4.9) are reported. Compounds 4.4, 4.5 and 4.6 contain one, two or three -NH2 moiety(ies), respectively. Compounds 4.7, 4.8 and 4.9 contain one, two or three –NMe2 moiety(ies), respectively. A systematic investigation has been carried out to rationalize the effect of donor-acceptor ratio on the ICT process in borylanilines 4.4-4.9. The aryl spacer between donor amine and acceptor boron is kept the same in all the compounds to avoid the electronic effect of spacer on the ICT characteristics of these compounds. In the case of compounds 4.4-4.6, the increase in the number of donor -NH2 moieties does not affect their absorption profile, while in the case of compounds 4.7-4.9, the absorption spectra are shifted bathochromically with an increase in the number of donor-NMe2 moieties. Photoluminescence (PL) of 4.4-4.6 is significantly blue shifted with an increase in number of –NH2 moieties, while the PL of 4.7-4.9 was slightly blue shifted. The absorption and PL features of 4.4-4.6 are sensitive to the polarity of the solvent medium. In contrast, absorption profiles of 4.7-4.9 are not sensitive to the polarity of the solvent medium. The PL of these compounds is affected by the polarity of the solvent medium. Chapter 5 This chapter deals with triarylboron based fluorescent probes (5.1-5.4) for the selective detection of thiophenols over aliphatic thiols. The probes were constructed by conjugating luminescent borylanilinies with luminescent quencher 2,4-dinitrobenzene sulfonyl (DNBS) moiety. In compound 5.1 and 5.2 the DNBS moiety is positioned at the para position with respect to the triarylborane moiety, while in 5.3 and 5.4 the DNBS moiety(ies) is(are) at the meta position(s). Probes 5.1-5.4 showed selective turn-on fluorescence response towards thiophenol. The fluorescence “off-on” switching mechanism of 5.1-5.4 against thiophenols was fully elucidated by theoretical calculations. Probes 5.1-5.4 are also capable of detecting thiophenols in the intra cellular environments. Chapter 6 Design, facile synthesis and aggregation induced emission properties of a new series of novel triarylboron tethered N-aryl-1,8-naphthalimides (TAB-NPIs) 6.1-6.7 are described in this chapter. Systematic structural perturbation has been used for fine-tuning the optical and morphological properties of TAB- NPIs in both solid as well as in aggregated state. Compounds 6.1-6.7 are weekly luminescent in solutions. In contrast, all compounds (except compound 6.4) are strongly luminescent in the solid state and aggregated state in THF-H2O mixtures. The presence of sterically hindered boryl unit in 6.1-6.7 has endowed these molecules with unique AIE characteristics by preventing co-facial arrangements of NPI moieties. The propeller shape arrangement of TAB moiety in 6.1, 6.2, 6.5, 6.6 and 6.7 effectively prevents the aggregation induced emission quenching (AIEQ) and induce strong emission in the condensed state. In the solid state, compounds 6.1, 6.4, 6.5, and 6.6 generate an interesting supramolecular structure via intermolecular C-H--- and C-H---O interactions. No face to face intermolecular π---π interactions were found in the crystal structures of 6.1, 6.4, 6.5, and 6.6. This precludes the excimer formation which can be detrimental to the radiative process in these molecules. The scanning electron microscopy (SEM) images of as prepared samples of 6.1-6.7 clearly indicate that the morphology of these compounds strongly depends on the molecular conformations and number of naphthalimide moieties in the TAB-NPI conjugates. Chapter 7 This chapter deals with design, synthesis and optical properties of novel dimesitylboryl appended perylenediimides. A simple synthetic strategy has been developed for the construction of novel TAB-PDIs conjugates. These conjugates can be conveniently synthesised by condensation of boryl anilines with perylene tetracarboxylic acid anhydride. The incorporation of TAB moiety enhanced the solubility of perylen bisimides in common organic solvents. The PL quantum yield of both 7.1 and 7.2 strongly depends on the excitation wavelength. Lower Pl efficiency observed for 7.1 and 7.2 upon excitation in the boryl dominated absorption region may be due to the photon induced electron transfer form mesityl units of boryl to perylene bisimide moiety. The morphology as well as emission colours of supramolecular architectures of both 7.1 and 7.2 can be modulated by controlling the concentrations of DCM solutions of these compounds. Both the compounds showed selective fluorogenic response for F-1 and CN-1 anions. The simple synthetic strategy reported in this chapter can be conveniently exploited for the construction of TAB conjugates of semiconducting organic anhydrides. Chapter 8 Novel planar chiral Lewis acids 8.3(SP, SS), 1-phosphino-2-borylferrocenes 8.4(SP) and 2-phosphino-1-borylferrocenes 8.4(RP) have been synthesized from a readily accessible ferrocene sulphinate precursor. Adopting a simple synthetic approach and a single precursor, enantiomerically pure SP and RP isomers have been prepared. It would be worthwhile to investigate the catalytic properties of compounds 8.3(SS), 8.4(SP) and 8.4(RP). It would also be interesting to replace the mesityl groups on boron with other electron deficient groups like pentafluorophenyl and 1,3,5-trifluoromethylphenyl to fine tune the Lewis acidity of boron center and to set-up a general route to enantiomerically pure Planar Chiral Frustrated Lewis Pairs (PCFLP’s).

Triarylborane Functionalized Dicyanovinyl and Acetylacetone Based Molecular Platforms: Building Blocks for Multiple Anion Sensors and Efficient Phosphorescence Emitters The main objective of this thesis is to design a simple strategy for triarylborane based multiple anion sensors and development of triarylborane incorporated phosphorescent metal complexes. The thesis consists of eight chapters and the contents of each chapter are given below. Chapter 1 This chapter gives a general introduction to recent advances relevant to the theme of the thesis. A review of the fundamental characteristics of triarylboranes and their applications in various fields such as chemical sensors and optoelectronics is presented. Advances in boron chemistry in the areas such as anion sensors, solid state emissive and phosphorescence materials are discussed in detail. The scope of the thesis is outlined at the end of the chapter. Chapter 2 The second chapter deals with the general experimental techniques and synthetic procedures followed in this thesis. Chapter 3 This chapter deals with a rational design strategy for differential identification of fluoride and cyanide ions using TAB based sensors. In general, most of the triarylboranes give similar optical responses towards fluoride and cyanide ions as they follow similar sensing mechanism. In order to circumvent this problem, two TAB-DCV conjugates (1 and 2) are designed and synthesised. The DCV unit is highly specific for cyanide ion owing to the presence of electrophilic carbon center. Probes 1 and 2 differ in steric crowding around the boron center. The less crowded boron center in 1 binds with fluoride as well as with cyanide ions giving similar optical response (luminescence is quenched in presence of F¯ and CN¯). In the case of 2, selectivity of boron center towards fluoride is tuned by increasing the steric crowding around the boron unit. The dicyanovinyl unit acts as selective sensing site for cyanide ions. As a result, 2 gives different fluorogenic response towards the anions F¯ and CN¯ which were considered as interfering anions in TAB based sensor chemistry. Thus, a modular design principle is developed for differential identification of fluoride and cyanide ions using TAB. Chapter 4 In this chapter, detailed photophysical studies of TAB-amine-DCV conjugates and colorimetric discrimination of fluoride and cyanide ions are discussed. Presence of amine based donor between the two electron deficient sites enhances the electronic conjugation in 3−5. Since there are two different acceptor sites with a common donor, two distinct charge transfer transition bands are observed in the visible region of electromagnetic spectrum. The absorption and emission spectra of these compounds show pronounced sensitivity to solvent polarity, signifying large excited state dipolmonents. Anion binding studies confirms that these compounds are highly selective towards fluoride and cyanide ions. Fluoride ions selectively interact with boron center and block the corresponding charge transfer transition thereby leading to a distinct colour change which is observable by naked eye. On the other hand, cyanide interacts with boron as well as DCV unit and blocks both the charge transfer transitions which results in disappearance of colour. Hence, compounds 4 and 5 exhibit different colorimetric signals for fluoride and cyanide ions. Since the absorption bands of 3 do not fall in the visible region, it does not show any colorimetric response towards the aforementioned anions. The anion sensing mechanisms are established by 1H, and 19F NMR studies. Chapter 5 This chapter presents a systematic study of the effect of length of π-electronic conjugation on the optical properties and anion sensing abilities of a series of TAB-oligothiophene-DCV conjugates (6−8). Their absorption as well as emission bands undergo redshift upon increasing the number of thiophene units between TAB and DCV units as the π-electronic conjugation in 6−8 is greatly dependent on the number of thiophene units. Their fluorescence emission is highly sensitive to solvent polarity. In the case of 6, the emission band undergoes a redshift with reduced intensity. In the case of 7 the emission band undergoes a redshift but the intensity is not affected by solvent polarity. In the case of 8, the emission band undergoes redshift with enhanced intensity in polar solvents. Interestingly, 7 and 8 show solvent viscosity dependent fluorescence. Structural reorganisation is restricted in viscous medium and results in enhanced emission for 7 and 8. Further, these compounds exhibit selective response towards the fluoride and cyanide ions with different colorimetric responses. Test strips made up of probes 7 and 8 have potential application in identifying fluoride and cyanide ions in aqueous medium. Chapter 6 This chapter describes synthesis and optical characterisation of triarylborane incorporated acetylacetone (acacH) ligands (9, 10) and their borondifluoride complexes (11, 12). AcacH ligands and BF2 complexes show solvent dependent emission phenomena due to the involvement of charge transfer transition. Their optical properties are highly dependent on molecular conformations. Complex with duryl spacer (12) exhibits more red shifted emission in polar solvents due to the enhanced charge transfer transition facilitated by twisted rigid geometry. In presence of fluoride and cyanide ions, the borondifluoride complexes are not stable. The anions concomitantly interact with tricoordinate boron as well as acac-BF2 unit to give rise to complex pattern of photoluminescence spectral changes during the titration experiment. The binding pathway and the possible species involved are established with the help of 1H, 19F and 11B NMR spectral studies in presence of the anions. Complexes 11 and 12 act as selective chemodosimetric sensors for fluoride and cyanide ions. Chapter 7 In this chapter, the synthesis and optical characterisations of triarylborane conjugated cyclometalated platinum complexes are discussed. A series of square planar platinum complexes are synthesised with different cyclometalating ligands. Complexes (13−18) exhibit a range of luminescence from green to red in solution as well as in the solid state. Their emission intensities are highly sensitive towards atmospheric oxygen suggesting that they originate from a triplet excited state. A maximum of 85% quantum yield is observed for complex 15 in solution state while complex 14 showed a maximum of 58% quantum yield in solid state. Complexes with rigid molecular conformation (14, 16 and 18) showed higher luminescence quantum yield than those having phenyl spacer (13, 15 and 17). The sterically encumbered boryl (-BMes2) group significantly reduces π-π stacking between the square planar entities. Thus, complexes 13−18 show bright luminescence in solid state compared to model complexes without boryl group. The effect of Lewis acidic boron center on luminescence behaviour is explored by fluoride binding studies. Chapter 8 This chapter is divided into two parts. Part-I describes the synthesis and optical characterisation of triarylborane conjugated cyclometalated iridium complexes (19−24). They are brightly luminescent in solution state with high sensitivity towards atmospheric oxygen. Complex 20 shows a highest quantum yield of 91%. Interestingly, under ambient atmospheric conditions, they exhibit a rare type of dual emission. Life time data suggest that the lower energy emission band originates from cyclometalated iridium based triplet excited state while higher energy emission band originates from boryl ased singlet excited state. Fluoride binding at the boron site results in luminescence quenching; evidently, tri-coordinate boron has a major contribution to the luminescence features of these iridium complexes. Part-II deals with synthesis of triarylborane conjugated pyrazole ligand (25) and its binuclear iridium complexes (26−28) in which two iridium centers are bridged by hydroxo as well as pyrazolato ligands. These binuclear iridium complexes exhibit higher luminescence quantum yield than TAB-acac-Iridium complexes (mononuclear complexes; part I). Binding of fluoride ions at the boron center has a minor impact on their luminescence nature. High sensitivity of their luminescence towards atmospheric oxygen indicates the involvement of triplet excited state in their emission process.