This thesis presents the synthesis and characterisation of a range of heterometallated porphyrin oligomers and other novel 3D π-conjugated porphyrin nanostructures. Subsequently, their physical organic properties were evaluated which revealed some fascinating electronic properties. Chapter 1 summarises some of the work done in the Anderson group on porphyrin nanostructures and reviews the literature regarding heterometallated porphyrin oligomers. In addition it introduces the main concepts and techniques used in the remainder of the thesis. In Chapter 2 the stabilities of a family of four linear porphyrin pentamer complexes are determined by UV-vis-NIR titrations and analysed using chemical double-mutant cycles which reveal that the binding energy of the copper centre to an axial pyridine ligand is -6.2 kJ mol^-1. Subsequently, the Zn-Zn-Cu-Zn-Zn pentamer is used in the synthesis of a heterometallated 10-porphyrin nanoring. Chapter 3 will describe the investigation of quantum interference phenomena in a bis-copper six-porphyrin nanoring by using EPR spectroscopy. We show that the exchange coupling between two spin centres is increased by a factor 4.5 in the ring structure with two parallel coupling pathways as compared to an otherwise identical system with just one coupling path. In Chapter 4 the syntheses of three isomers of the bis-copper 6-porphyrin nanoring are described. DFT calculations have indicated potential destructive interference phenomena in one of the isomers which would allow for the formation of a molecular system with behaviour resembling that of a hypothetical molecular interferometer. Chapter 5 reports on the template-directed synthesis of a π-conjugated 14-porphyrin nanoball. This bicyclic structure consists of two intersecting nanorings of 6 and 10 porphyrin units. Fluorescence up-conversion spectroscopy experiments demonstrate that electronic excitation delocalises over the whole 3D π-system within 0.3 ps if the nanoball is bound to its templates or within 5 ps if the nanoball is empty. In Chapter 6 the synthesis and characterisation of a D_4h symmetric analogue of the porphyrin nanoball is described. The structure consists of ten porphyrin units arranged as two perpendicular 6-porphyrin nanorings intersecting at two porphyrins. In the synthesis, a combination of magnesium and zinc porphyrins are used which allows for the introduction of a selective demetallation method crucial for accessing this novel structure.

The preparation of the shape-persistent carbosilane-functionalized porphyrins H2TPP(4-SiRR’Me)4, Zn(II)- TPP(4-SiRR’Me)4 (R = R’ = Me, CH2CHvCH2, CH2 CH2CH2OH; R = Me, R’ = CH2 CHvCH2, CH2CH2CH2OH; TPP = tetraphenyl porphyrin), H2TPP(4-Si(C6H4-1,4-SiRR’Me)3)4, and Zn(II)-TPP(4-Si- (C6H4-1,4-SiRR’Me)3)4 (R = R’ = Me, CH2CHvCH2; R = Me, R’ = CH2CHvCH2) using the Lindsey condensation methodology is described. For a series of five samples their structures in the solid state were determined by single crystal X-ray structure analysis. The appropriate 0th and 1st generation porphyrin-based 1,4-phenylene carbosilanes form 2D and 3D supramolecular network structures, primarily controlled by either π–π interactions (between pyrrole units and neighboring phenylene rings) or directional molecular hydrogen recognition and zinc–oxygen bond formation in the appropriate hydroxyl-functionalized molecules. UV-Vis spectroscopic studies were carried out in order to analyze the effect of the dendritic branches on the optical properties of the porphyrin ring. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Organic semiconductors are widely studied as potential active components for consumer electronics due largely to their easily tuned properties and the promise of lower-cost solution-based processing technology. Imide-functionalized organic small molecule compounds have been one of the more important and studied organic semiconductors. However, very few imide-functionalized conjugated polymers have been reported in the literature. The body of this dissertation focuses on the synthesis, structure-property and device studies of imide-functionalized conjugated polymers. Reasons for choosing arylene imides as polymer building blocks include: a) they impart low-lying LUMOs to polymers, allowing band-gap engineering through choice of comonomers with variable electron-donating ability; b) imide-nitrogens provide points to attach side chains to manipulate solubility and solid-state packing; c) they are easily prepared. Structure-property studies include electrochemical measurements, UV-Vis absorption spectroscopy, differential scanning calorimetry (DSC), x-ray diffraction, and in some cases evaluation as active components in field-effect transistors (OFETs) and photovoltaic devices (PVDs). The published method to synthesize 3,6-dibromo-pyromellitic bisimides (PMBI) was streamlined and poly(phenylene ethynylene)s (PPEs) with variable band gaps were prepared from them (Chapter 2). As noted in all the chapters, electrochemical and optical measurements reveal that the LUMO of the polymers is indeed dictated by the arylene imide, while the HOMO, and therefore the optical energy gap is controlled through varying the electron donor monomer. Intramolecular hydrogen bonding was employed for increasing backbone coplanarity and therefore the polymer could have higher conjugation. One of these polymers demonstrated the narrowest band gap (1.50 eV) for any published PPE. Chapter 3 describes the first published conjugated copolymers from naphthalene bisimides (NBI), here using thiophene-based comonomers as donor units. Polymers with high molecular weight and decent solubility were obtained by choosing appropriate side chains. The optical energy gaps could be tuned across the visible and into the near IR. Preliminary OFET studies revealed electron mobility as high as ~0.01 cm2/Vs. One low band gap polymer provided OFETs with electron mobility of ~0.04 cm2/Vs and hole mobility of ~0.003 cm2/Vs, which is also among the highest mobilities of ambipolar polymeric semiconductors. Using the same approach as in Chapter 3, phthalimide-based monomers were incorporated into polymer backbones for developing new high performance p-type polymer semiconductors for OFETs and PVDs (Chapter 4). Some analogues based on benzothiadiazole, PMBI, and thiophene imides as acceptors were prepared for comparison. Again, high molecular weight, soluble polymers with band gaps spanning the visible and into the near IR were obtained. OFETs from one of the polymers yielded hole mobility ~0.3 cm2/Vs under ambient atmosphere without post-processing thermal annealing, which places it squarely within the state-of-the-art for conjugated polymers. Due to the high mobility and low band gap, this polymer also leads to PVDs with moderately good power conversion efficiency (PCE: ~2%).

Dans ce travail, des derivés du dithia[3.3]paracyclophane sont étudiés pour des applications en nanostructuration de surfaces et comme nouveaux fluorophores. Dans un premier temps, l'auto-assemblage supramoléculaire de molécules est utilisé pour créer des réseaux 2D sur surface. Cependant, l'utilisation de tels substrats a tendance à annihiler les propriétés électroniques des composés adsorbés. Par conséquent, des dérivés 3D du dithia[3.3]paracyclophane sont employées afin d'éloigner le composant actif de la surface. Dans cet optique, de nouvelles molécules à base de groupements pyridine ont été conçues pour s'auto-assembler sur différents substrats. Les caractérisations préliminaires ont été effectuées afin d'étudier les propriétés d'auto-assemblage de telles molécules seules ou co-adsorbées, et les premières images de réseaux 2D auto-organisés sur graphite et or ont été obtenues par microscopie à sonde locale. Dans un second temps, de nouveaux composés sont actuellement étudiés pour électroluminescence à haute rendement à partir de la fluorescence retardée à activation thermique (TADF). Ce phénomène est généralement observé pour des molécules montrant un faible gap électronique entre ses états excités singulet et triplet, lié au faible recouvrement des orbitales HOMO et LUMO localisées sur le donneur et l'accepteur, respectivement. Dans ce contexte, nous proposons un nouveau design de molécules de type donneur-accepteur où HOMO (donneur) et LUMO (accepteur) sont séparées par un cœur cyclophane. Nous avons synthétisé deux émetteurs et leurs propriétés photo-physiques ont été étudiées en solution et à l'état solide. / In this work and due to their unique electronic properties, 3D-dithia[3.3]paracyclophane-based molecules have been studied for surface nanostructuration applications and as new fluorophore. First, the supramolecular self-assembly of molecules is used to create well-organised 2D-networks on conducting surfaces. However, the use of such substrates tends to quench any electronic properties of the adsorbed molecules. In this context, 3D-dithia[3.3]paracyclophane-based molecules were employed to lift up the active moiety from the surface. In this work, new pyridyl end-capped molecules were designed to self-assemble on any substrate. Preliminary characterisations were performed to study the supramolecular self-assembly of such molecules alone or with co-adsorbers, and the first images of organised 2D-networks on graphite and gold have been obtained by scanning probe microscopy. Second, the design of new and efficient emitter is a hot topic for the fabrication of OLED devices. A new type of compounds is currently investigated for their high electroluminescence efficiency due to thermally activated delayed fluorescence (TADF). This phenomenon is expected from molecules showing low electronic gap between singlet and triplet excited states, which is related to a low overlap of the HOMO and LUMO, localised on the electron-door and acceptor moieties of the molecule, respectively. In this sense, we propose a new design of donor-acceptor molecules where the HOMO (donor) and LUMO (acceptor) are separated by a cyclophane core. We synthesised a couple of emitters and their photophysics properties were studied in solution and in solid state.

The preparation of the shape-persistent carbosilane-functionalized porphyrins H2TPP(4-SiRR’Me)4, Zn(II)- TPP(4-SiRR’Me)4 (R = R’ = Me, CH2CHvCH2, CH2 CH2CH2OH; R = Me, R’ = CH2 CHvCH2, CH2CH2CH2OH; TPP = tetraphenyl porphyrin), H2TPP(4-Si(C6H4-1,4-SiRR’Me)3)4, and Zn(II)-TPP(4-Si- (C6H4-1,4-SiRR’Me)3)4 (R = R’ = Me, CH2CHvCH2; R = Me, R’ = CH2CHvCH2) using the Lindsey condensation methodology is described. For a series of five samples their structures in the solid state were determined by single crystal X-ray structure analysis. The appropriate 0th and 1st generation porphyrin-based 1,4-phenylene carbosilanes form 2D and 3D supramolecular network structures, primarily controlled by either π–π interactions (between pyrrole units and neighboring phenylene rings) or directional molecular hydrogen recognition and zinc–oxygen bond formation in the appropriate hydroxyl-functionalized molecules. UV-Vis spectroscopic studies were carried out in order to analyze the effect of the dendritic branches on the optical properties of the porphyrin ring. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

This thesis explores the design, synthesis and optoelectronic properties of supramolecular photoactive materials based on chiral iridium(III) and ruthenium(II) metalloligands. Our design strategies aim to create a high concentration of chromophoric units that, when self-assembled in well-defined geometrical arrangements, exhibit emergent photophysical properties.

The work highlighted in this dissertation comprises of syntheses and characterizations of coordination driven supramolecular compounds. The synthesized complexes are characterized by IR spectroscopy, multinuclear NMR spectroscopy and single crystal structure determination. Chapter 2: In this chapter we attempted to make a three dimensional self-assembled cage by the reaction between N, N’, N’’- tris(3-pyridyl)trimesic amide a tritopic donor and Pt(II) based 90° ditopic acceptor cis-(dppe)Pt(II)(OTf)2 [dppe = 1,2-bis(diphenylphosphino)ethane]. It resulted in a trigonal bipyramidal structure. The cage was characterized by single crystal XRD and FT-IR spectra. Chapter 3: In this chapter we have reported the synthesis and characterization of two hereby unknown metal containing carboxylic acid ligands containing the Pt-ethynyl moiety. Also we have shown the preparation and structure analysis of a copper containing metal-organic framework incorporating one of the Pt-ethynyl containing carboxylic acid ligand. This has resulted in the formation of a very interesting hetero-metallic MOF which is quite uncommon in literature.

Self–assembly has long been attracting chemists’ attention because it can yield fascinating supramolecular architectures in a single step. More precisely, metal–ligand coordination–driven self–assembly has stood out as an efficient methodology in this paradigm due to simple design principle and high predictability of the final molecular architectures. Moreover, one can envisage hierarchical nanoscopic molecular architectures with a vast range of size, shape and functionality via this methodology. Two–component self–assembly (involving one type of donor and one type of acceptor) is relatively easy to monitor and a widely used protocol. Whereas, multicomponent self–assembly (involving more than one types of donors/or acceptors) is too complex due to the possibility of formation of several products. The prime advantage of multicomponent self–assembly lies in one–pot construction of topologically complicated multifunctional architectures. Template– induced multicomponent self–assembly of discrete architectures is recently investigated to some extent. But, template–free multicomponent self–assembly of discrete architectures is rare in the literature. Physico–chemical property of a self–assembled product is coded in the functional groups present in its precursor building units. Functional supramolecular architectures have important applications in many potential fields such as chemosensing, drug delivery, supramolecular catalysis, etc. Porphyrin, pyrazole, imidazole, etc. functionalized organic molecules are hydrophilic as well as hydrophobic in nature. Introduction of such functionality in building units can lead to amphiphilic supramolecular complexes. Therefore, such complexes can be employed as hosts for versatile guests, or as molecular reactors for various chemical reactions. In general, counter ions block the cavity of ionic molecular architectures. Thus, when ionic molecular architectures are employed as hosts, they cannot fully provide their cavity towards guest molecules. In contrast, neutral molecular complexes are expected to be better hosts. It is well known that alkenyl/alkynyl heavy metal complexes exhibit efficient chemoluminescence due to facile metal to ligand charge transfer (MLCT). Hence, such complexes can be employed as efficient chemosensors towards the detection of electron deficient molecules such as nitroaromatics which are the chemical signatures of many powerful explosives. In these regards, a considerable effort is being paid recently to design and construct various functional supramolecular architectures. Symmetry and rigidity of building units increase predictability of the final product in self– assembly. In this regard, symmetric; rigid Pd(II)/Pt(II)–based acceptors and polypyridyl donors are explored extensively in metal–ligand coordination–driven self–assembly. In contrast to rigidity, flexibility endows building units to adopt thermodynamically most stable conformer/architecture. Hence, same set of building units can render different conformers/architectures in presence of different templates for the sake of suitable host–guest interactions. Contrary to high symmetry, asymmetry in building units leads to molecular architectures with polar environments. But, due to the possibility of formation of several isomeric products from the self–assembly involving such building units, it is difficult to monitor the reaction and purify the products. Hence, designing appropriate synthetic routes which can lead to formation of single isomeric products possessing flexible/asymmetric building units is a challenge to synthetic chemists. Investigations incorporated in the present thesis are focused to design and construct various 2D/3D discrete supramolecular architectures employing self–assembly of mainly Pd(II)/Pt(II) acceptors with N/O donors. Elemental analyses, IR/NMR/UV–Vis/fluorescence/mass spectroscopy and single crystal X–ray diffraction analysis are among prime techniques employed for characterization of the reported architectures. For a few cases, powder X–ray diffraction (PXRD) analysis and density functional theory (DFT) calculations are also carried out. CHAPTER 1 of the thesis provides a brief general introduction to self–assembly and supramolecular chemistry. It emphasizes on the metal–ligand coordination–driven self–assembly approach towards the construction of a library of 2D/3D supramolecular architectures. CHAPTER 2 describes formation of a series of template–induced and template–free discrete 3D Pd(II) molecular prisms via multicomponent self–assembly. Because of the possibility of formation of several products, multicomponent self–assembly is difficult to monitor. For example, several molecular architectures are expected from a three–component self–assembly involving a 90° acceptor [ca. cis–blocked Pd(II)], a 120° tritopic donor [ca. benzene–1,3,5– tricaboxylate (tma)] and a 180° donor [ca. 4,4'–bipyridine (4,4'–bpy) or pyrazine (pz)]. Interestingly, treatment of cis–(tmen)Pd(NO3)2 [tmen = N,N,N′,N′–tetramethylethylenediamine] with 4,4'–bpy and K3tma in 6 : 3 : 2 molar ratio at room temperature resulted in mainly a nanoscopic molecular trigonal prism [{(tmen)Pd}6(bpy)3(tma)2](NO3)6 (1) with three 4,4'–bpy pillars, two tma caps and six cis–(tmen)Pd connectors (Scheme 1). Scheme 1: Schematic representation of the formation of multicomponent self–assembled molecular trigonal prisms 1, 2 and 3. Surprisingly, the same reaction in presence of benzene–1,3,5–tricaboxylic acid (H3tma) as guest yielded exclusively the guest–encapsulated analogous molecular prism [{(tmen)Pd}6(bpy)3(tma)2(H3tma)2](NO3)6 (2; Scheme 1). It is also presented how variation of steric crowding at connectors (acceptors) influenced final outcomes. Self–assembly of cis– (en)Pd(NO3)2 [en = ethylenediamine] with 4,4'–bpy and K3tma in 6 : 3 : 2 molar ratio at room temperature resulted in a triply interlocked nanoscopic 3D coordination cage [{(en)Pd}6(bpy)3(tma)2]2(NO3)12 (3; Scheme 1). It is also shown that above trend is followed even upon changing the pillar length from 4,4'–bpy to pz. Aromatic –stacking interactions amog tma caps as well as among 4,4'–bpy pillars provided considerable stability to interlocked archirecture 3. Steric crowding due to the methyl groups in cis–(tmen)Pd connectors hindered intercalation and hence led to non–interlocked architecture 1. As expected, similar self–assembly using moderately crowded acceptor cis–(pn)Pd(NO3)2 [pn = 1,2–diaminopropane] with same donors 4,4'–bpy and K3tma resulted in a mixture of analogous triply interlocked and non– interlocked architectures in solution though it was found to be only triply interlocked architecture in solid state. Interestingly, irrespective of the steric crowding of the blocking amines, self– assembly in presence of H3tma as guest preferred exclusive formation of guest–encapsulated prisms of type 2 (Scheme 1). This is due to considerable stabilazation via aromatic –stacking interactions amog tma caps and H3tma guests. Formation of guest–free discrete molecular prisms (such as 1) and triply interlocked coordination cages (such as 3) were confirmed by spectroscopic and single crystal X–ray diffraction analyses. Whereas, formation of guest– encapsulated discrete molecular prisms (such as 2) was established by DOSY, ROESY 2D NMR spectroscpic study in conjunction with energy optimized geometry analysis. CHAPTER 3 reports design and syntheses of a series of porphyrin functionalized nanoscopic 3D molecular open prisms. Self–assembly of a C4 –symmetric tetratopic donor with a 90° ditopic acceptor can, in principle, lead to several architectures such as trigonal; tetragonal; pentagonal; hexagonal; etc. open prisms, closed cube or 1D oligomers. Both of 1,5,10,15–tetrakis(4– 12 pyridyl)porphyrin (L) and 1,5,10,15–tetrakis(3–pyridyl)porphyrin (L) possess pseudo C4 – 1 symmetry. Surprisingly, treatment of Lwith the 90° ditopic acceptor cis–(dppf)Pt(OTf)2 [dppf = diphenylphosphinoferrocene, OTf = trifluoromethanesulphonate] yielded exclusively an 1 unprecedented [6 + 12] self–assembled hexagonal open prism [(dppf)12Pt12L6](OTf)24 (4; Scheme 2). Scheme 2: Schematic representation of formation of [6 + 12] self–assembled molecular hexagonal open prism 4 and its Zn(II) embedded complex 4a. 2 In contrast, [3 + 6] self–assembled trigonal open prisms are adopted upon self–assembly of Lwith Pd(II)–based 90° ditopic acceptors. These complexes show facile incorporation of Zn(II) ions into porphyrin N4 –pockets. Moreover, they incorporate high microporosity in solid state and they are amphiphilic in nature due to porphyrin functionality. One of the trigonal open prisms revealed its considerably high adsorbate–adsorbent affinity towards non–polar gas such as N2 and protic solvent vapors such as water, methanol and ethanol. Formation of hexagonal and trigonal open prisms is fully authenticated by spectroscopic and single crystal X–ray diffraction analyses. CHAPTER 4 describes design and synthesis of a pyrazole functionalized flexible donor (L) and its self–assembly towards the construction of three nanoscopic 3D supramolecular discrete cages 5–7 (Scheme 3). Scheme 3: Schematic representation of formation of [4 + 6] self–assembled molecular double–square 5 and [2 + 3] self–assembled molecular trigonal bipyramids 6–7. 3 Due to flexibility, Lcan adopt different conformations and hence several isomeric architectures 3 are expected upon self–assembly. For example, self–assembly of Lwith a rigid ditopic 90° acceptor can lead to trigonal bipyramid (TBP), double–square, adamantanoid or truncated 3 tetrahedron. Treatment of Lwith cis–(tmen)Pd(NO3)2 yielded a [4 + 6] self–assembled double–3 square [(tmen)6Pd6L4](NO3)12 (5; Scheme 3). Much to our surprise, replacement of cis– (tmen)Pd(NO3)2 with CuCl2 or AgOTf yielded [2 + 3] self–assembled molecular TBP 33 [Cu3Cl6L2] (6) or [Ag3L2](OTf)3 (7), respectively (Scheme 3). CHAPTER 5 presents study of self–assembly involving flexible asymmetric donors and rigid 4 symmetric 90° acceptors. Three ambidentate donors 5–pyrimidinecarboxylate (L), nicotinate–56 N–oxide (L) and isonicotinate–N–oxide (L) were employed in self–assembly with symmetric rigid 90° acceptors cis–(dppf)M(OTf)2 [M = Pd(II)/Pt(II)]. Due to flexibility and different 464 connectivity of these donors L–L, several linkage isomers are expected. Treatment of Lwith cis–(dppf)M(OTf)2 in 1 : 1 molar ratio resulted in exclusive formation of single linkage isomeric 4 [3 + 3] self–assembled symmetric molecular triangles [(dppf)3M3L3](OTf)3 (8: M = Pd and 9: M = Pt), where the donors connected to metal centers in head–to–tailfashion (Scheme 4). Similar 56 reactions of Land Lwith cis–(dppf)M(OTf)2 resulted in self–sorting of [2 + 2] self–assembled molecular rhomboids 10–13 (Scheme 4). Exclusive self–selection of single linkage isomeric architectures 8, 9, 10 and 12 was fully established by spectroscopic as well as single crystal X– ray diffraction analyses. Though we could not obtain suitable X–ray diffraction quality single crystals of 11 and 13, exclusive formation of single isomeric [2 + 2] self–assembled rhomboids 131 was established by multinuclear NMR (H and P) in conjunction with ESI–MS spectroscopic studies. Scheme 4: Schematic representation of formation of complexes 8–13. Part A of the CHAPTER 6 describes how two neutral organometallic mononuclear chelates are formed upon treatment of disodium fumarate (,–unsaturated dicarboxylate) with cis– (dppf)Pd/Pt(OTf)2 at ambient conditions. Reaction of 90acceptors cis–(dppf)Pd/Pt(OTf)2 with fumarate is expected to result in [4 + 4] self–sorted molecular squares/or [2 + 2] self–sorted molecular rhomboids (Scheme 5). To our surprise, the above reactions led to an unusual reduction of C–C double bond followed by concomitant formation of mononuclear chelates [M(dppf)(C4H4O4)] (M = Pd for 14 and Pt for 15) via coordination with one of the carboxylate oxygen atoms and –carbon to metal centers (Scheme 5). Scheme 5: Schematic representation of formation of the complexes 14–15. Part B of the CHAPTER 6 describes design and synthesis of a novel shape selective “clip” 1 shaped bimetallic Pd(II) acceptor Mand its self–assembly with disodium fumarate to construct a neutral tetrametallic Pd(II) supramolecular rectangle 16 (Scheme 6, left). Similarly, a shape selective 180° bimetallic Pd(II) acceptor was also synthesized and employed in self–assembly with several “clip” shaped organic donors to achieve several cationic tetrametallic Pd(II) supramolecular rectangles. Scheme 6: Schematic representation of the formation of neutral Pd4 (left) and Pd2 (right) molecular rectangles. Moreover, synthesis of a neutral bimetallic Pd(II) molecular rectangle 17 via one–pot reaction of trans–(PEt3)2PdCl2 with 1,8–diethynylanthracene (Scheme 6, right) is also presented herein. These –electron rich rectangles exhibit prominent chemoluminescence. Chemosensitivity of these complexes towards the detection of electron deficient nitroaromatics via fluorescence study is also discussed in details in this section. (Pl refer the abstract file for figures).

Applications of conjugated polymer (CPs) in optoelectronic devices are critically depend on nature of thin film morphology. In thin film of CPs, the distribution of conjugation length is highly heterogeneous because of conformational defects, distortions of polymer chain and aggregates. A greater understanding of the self-assembly properties of polymer in solution, in particular control over aggregation leads to richer description of electronic properties and hence reproducible fabrication of thin film devices. Recently, chiral CPs have attracted profound interest because of their promising chiroptical properties in thin films and easy control over the selective agglomeration process. In this thesis, we have investigated the role of chiral side-chains on a series of thiophene diketopyrrolopyrrole (TDPP)-benzodithiophene (BDT) based copolymers. Chiral 3,7-dimethyloctyl chain was introduced as an asymmetric chain to incorporate chirality on one of the repeating unit (TDPP) of copolymers. Two polymers with side-chains of identical chirality (S),(S)-PTDPP-BDT; (R),(R)-PTDPP-BDT and a third polymer with similar side-chains of opposite chirality (R),(S)-PTDPP-BDT were synthesized. The chiroptical properties were investigated by UV-visible and circular dichroism (CD) spectroscopy. Figure 1: The structure of the TDPP-BDT copolymers. The copolymers dissolved in a good solvent (e.g. chloroform, chlorobenzene) in which polymers adopts random coil conformation, no chiral response has been observed. However, a critical addition of non-solvent (methanol), the copolymers stack in a chiral fashion and leads to typical bisignate Cotton effects. It is noteworthy that the two polymers, (S),(S)-PTDPP-BDT and (R),(R)-PTDPP-BDT exhibiting a nearly ideal mirror-image relationship in CD spectra (Figure 2a) whereas the (R),(S)-PTDPP-BDT lacks chiropticity even with the addition of methanol. The aggregation induced CD phenomena are dependent on the temperature of solution and do not exhibit reversibility in a heating-cooling cycle. Figure 2: (a) The mirror image Cotton effects of (S),(S)-PTDPP-BDT and (R),(R)-PTDPP-BDT (b) No CD signal was observed for the (R),(S)-PTDPP-BDT polymer. Figure 3: The variation of (a) UV-vis and (b) CD spectra of (R),(R)-PTDPP-BDT polymer with thickness of the solid film. To investigate the role of thickness and annealing temperature on optical and chiroptical properties of polymer films, thin films were prepared using drop-casting method from a solution of chlorobenzene. Both the polymer showed gradual enhancement of CD signal with the increase of film thickness but we did not see any such order with temperature (Figure 3). Figure 4: The morphology observed for the film by (a) AFM; (b); (c) FESEM. The thin film morphology of polymers is characterized by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) (Figure 4). AFM studies show the polymer molecules self-assembled and formed interconnected nanofibers. Whereas FESEM images clearly revealed that, the nanofibers of polymers are predominantly stack in a chiral fashion and mimic a one-handed helix which leads to bisignate Cotton effects. The (S),(S)-PTDPP-BDT and (R),(R)-PTDPP-BDT form fibers with opposite handedness whereas (R),(S)-PTDPP-BDT do not have such preferred handedness. The research described in this thesis aims to explore the role of chiral side-chains to impose chiral stacking and hence resulting chiral expression. Chirality in this class of polymers may endows them promising optoelectronic properties. (For figures pl see the abstract pdf file)

Over the past few decades, supramolecular self-assembly has become an alternative synthetic tool for constructing targeted discrete molecular architectures. Among various interactions, metal-ligand coordination has attracted great attention owing to high bond enthalpy (15−50 Kcal/mol) and predictable directionality. The basic principle of metal-ligand directed self-assembly relies on the proper designing of information encoded rigid complementary building units (a transition metal based acceptor and a multidentate organic donor) that self-recognize themselves in a chemically reasonable way (depends on their bite angle and symmetry) during self-assembly process. As far as acceptor units are concerned, Pd(II) and Pt(II) metal-based cis-blocked 90° acceptors have so far been used greatly for the construction of a library of 2D/3D discrete supramolecular architectures due to their rigid square planar geometry and kinetic lability. However, in some cases the efforts to design finite supramolecular architectures using a cis-blocked 90° acceptor in combination with a bulky donor ligand were unsuccessful, which may be due to the steric demands of donor ligand. Moreover, the resulted assemblies from such cis-blocked 90° building unit are mostly non-fluorescent in nature and limit the possibility of using them as chemosensors for various practical applications. Unlike that of rigid square-planar Pt(II) and Pd(II)-metal based building blocks, the use of other transition metal-based building units for the construction of discrete nanoscopic molecular architectures are known to lesser extent, mainly because of their versatile coordination geometries. However, some of the half-sandwiched piano-stool complexes of late transition metals like Ru, Os, Ir and Rh are known to maintain the stable octahedral geometry under various reaction conditions. Moreover, the self-assembly using redox active transition metal-based building units may lead to redox active assemblies. On the other hand, symmetrical rigid donors have been widely used as the favorite choices for the purpose of constructing desired product mainly due to their predictable directionality. Flexible linkers are not predictable in their directionality during self-assembly process and thus results mostly in undesired polymeric products. Furthermore, metal-ligand directed self-assembly provides opportunity to introduce multifunctionality in a single step within/onto the final supramolecular architectures. Among various functional groups, the incorporation of unsaturated ethynyl functionality is expected to enrich the final assemblies to be π-electron-rich and the attachment of ethynyl functionality with heavy transition metal ions are known to be luminescent in nature due to the facile metal to ligand charge transfer (MLCT). Hence, the final supramolecular complexes can be used as potential fluorescence sensors for electron-deficient nitroaromatics, which are the chemical signature of most of the commercially available explosives. The main thrust of the present investigation is focused on the judicious design and syntheses of multifaceted 2D/3D supramolecular architectures of finite shapes, sizes and functionality using Pt(II)/Ru(II) based “shape-selective” organometallic building blocks and investigation of their application as chemosensors. CHAPTER 1 of the thesis presents a general review on the core concepts of self-assembly and supramolecular chemistry. In particular, it underlines the importance of metal-ligand directional bonding approach for designing a vast plethora of discrete 2D/3D supramolecular architectures with tremendous variation in topology. CHAPTER 2 describes the design and syntheses of a series of 2D metallamacrocycles using carbazole-functionalized shape-selective 90° building units. A new Pt2II organometallic 90° acceptor 3,6-bis[trans-Pt(PEt3)2(NO3)(ethynyl)]carbazole (M1) containing ethynyl functionality is synthesized via Sonagashira coupling reaction and characterized. The combination of M1 with three different flexible ditopic donors (L1−L3) afforded [2 + 2] self-assembled molecular squares (1−3), respectively [where L1 = 1,3-bis(4-pyridyl)isophthalamide; L2 = 1,3-bis(3-pyridyl)isophthalamide; L3 = 1,2-bis(4-pyridyl)ethane] (Scheme 1). Scheme 1: Schematic presentation of the formation of a series of [2 + 2] self-assembled molecular squares. An equimolar (1:1) combination of same acceptor M1 with rigid linear ditopic donors (L4-L5) yielded [4 + 4] self-assembled octanuclear molecular squares 4 and 5, respectively [L4 = 4,4’-bipyridine; L5 = trans-1,2-bis(4-pyridyl)ethylene]. Conversely, a similar reaction of M1 with an amide-based unsymmetrical linear flexible ditopic donor L6 resulted in the formation a [2 + 2] self-sorted molecular rhomboid (6a) as a single product [L6 = N-(4-pyridyl)isonicotinamide]. Despite the possibility of several linkage isomeric macrocycles (rhomboids, triangles and squares) due to different connectivity of the ambidentate linker, the formation of a single and symmetrical molecular rhomboid 6a as an exclusive product is an interesting observation. This chapter also presents the synthesis and characterization of a complementary 90° dipyridyl donor 3,6-bis(4-pyridylethynyl)carbazole (L7). Stoichiometric combination of L7 with several PdII/PtII-based 90° acceptors (M2−M4) yielded [2 + 2] self-assembled molecular “bowl” shaped macrocycles (7−9) respectively, in good yields [M2 = cis-(dppf)Pd(CF3SO3)2; M3 = cis-(dppf)Pt(CF3SO3)2; M4 = cis-(tmen)Pd(NO3)2]. All these newly synthesized macrocycles were characterized by various spectroscopic techniques and molecular structures of some of them were confirmed by single crystal X-ray diffraction analysis. In addition to their syntheses and characterization, fluorescence chemosensing ability for various analytes was investigated. Macrocycle 1 is a system composed of amide-based receptor units and carbazole-based fluorophore moieties. The fluorescence study of 1 elicited a dramatic enhancement in the fluorescence intensity upon gradual addition of P2O74- anion in DMF/H2O solvent mixture, whereas similar titration under identical condition with other anions like F-, ClO4-, and H2PO4- did not show such change. Hence, molecular square 1 can be used as selective fluorescence sensor for pyrophosphate (P2O74-) anion. Due to their extended π-conjugation, macrocycles 3-4 were used as fluorescence sensors for electron-deficient nitroaromatics, which are the chemical signatures of many commercially available explosives. The fluorescence study showed a marked quenching of initial fluorescence intensity of the macrocycles(3-4) upon gradual addition of picric acid (PA) and they exhibited large fluorescence quenching responses with high selectivity for nitroaromatics among various other electron deficient aromatic compounds tested. As macrocycle 7 has large concave aromatic surface, it was utilized as a suitable host for large convex guest such as fullerene C60. The fluorescence quenching titration study suggested that macrocycle 7 forms a stable ~1:1 host-guest complex with C60 and the calculated association constant (KSV) is 1.0 × 105 M-1. CHAPTER 3 presents two-component coordination-driven self-assembly of a series of [2 + 2] molecular rectangles and a [2 + 4] self-assembled molecular tetragonal prism. An equimolar combination of pre-designed linear PtII2-acceptors M5−M6 separately with three different “clip” donors (L2, L8−L9) led to the formation of [2 + 2] self-assembled tetranuclear cationic molecular rectangles (10−15), respectively [M5 = 1,4-bis[trans-Pt(PEt3)2(NO3)(ethynyl)] benzene; M6 = 4,4’-bis[trans-Pt(PEt3)2(CF3SO3)(ethynyl)]biphenyl; L8 = 1,3-bis(3-pyridyl)ethynylbenzene; L9 = 1,8-bis(4-pyridyl)ethynylanthracene]. Rectangles 10-15 showed strong fluorescence in solution owing to their extended π-conjugation. Amide-functionalized rectangle 10 was used as a macrocyclic receptor for dicarboxylic acids. Solution state fluorescence study showed that rectangle 10 selectively binds (KSV = 1.4 × 104 M-1) with maleic acid by subsequent enhancement in emission intensity and addition of other analogous aliphatic dicarboxylic acids such as fumaric, succinic, adipic, mesaconic and itaconic acids causes no change in the emission spectra; thereby demonstrated its potential use as macrocyclic receptor in sensor applications. Since rectangle 15 is enriched with π-conjugation, it was examined as a fluorescence sensor for electron-deficient nitroaromatics such as picric acid, which is often considered as a secondary chemical explosive. The fluorescence study of 15 showed a significant quenching of initial emission intensity upon titrating with picric acid (PA) and it exhibited the largest fluorescence quenching response with high selectivity for picric acid. Scheme 2: Schematic representation of formation of [2 + 4] self-assembled of molecular tetragonal prism. This chapter also describes two-component coordination [2 + 4] self-assembly of a pyrene-based PtII8 tetragonal prism (16) as shown in Scheme 2, using a newly designed tetratopic organometallic acceptor (M7; 1,3,6,8-tetrakis[trans-Pt(PEt3)2(NO3)(ethynyl)]pyrene) in combination with an amide-based “clip” donor (L2) and propensity of this prism (16) as a selective fluorescence sensor for nitroaromatic explosives has been examined both in solution as well as in thin-film. CHAPTER 4 reports the synthesis and structural characterization of a series of Ru(II)-based bi-and tetra-nuclear metallamacrocycles and hexanuclear trigonal prismatic cages. In principle, the self-assembly of a “clip” acceptor with an asymmetrical ditopic donor is expected to give two different linkage isomeric (head-to-tail and head-to-head) molecular rectangles because of different bond connectivity of the donor. However, the equimolar combination of half-sandwiched p-cymene binuclear Ru(II)-based “clip” acceptors (M8−M9) and an amide-based ambidentate donor (L6) resulted in the self-sorting of single linkage (head-to-tail) isomeric rectangles 17−18 as only products, respectively [M8 = [Ru2(μ-η4-C2O4)(MeOH)2(η 6-p-cymene)2](CF3SO3)2; M9 = [Ru2(μ- η4-C6H2O4)(MeOH)2(η 6-p-cymene)2](CF3SO3)2]. Molecular structures of these head-to-tail linkage isomeric rectangles were unambiguously proved by single crystal X-ray diffraction analysis. Likewise, the self-assembly of oxalato-bridged Ru(II) acceptor M8 with a rigid dipyridyl “clip” donor L8 yielded a tetranuclear cationic pincer complex 19, while a similar reaction of M8 with an anthracene-functionalized “clip” donor L9 having shorter distance (between their reactive sites) compared to L8 led to the formation of [1 + 1] self-assembled macrocycle 20. This chapter also represents the design and synthesis of two hexanuclear trigonal prismatic cages (21−22) from the self-assembly of a π-electron rich tripyridyl donor (L10; 1,3,5-tris(4-pyridylethynyl)benzene) in combination with binuclear acceptors M8 and M9, respectively (Scheme 3). Formation of these prismatic cages was initially characterized using various spectroscopic techniques and the molecular structure of oxalato-bridged prism 21 was confirmed by single crystal X-ray diffraction analysis. In addition to the structural characterization, the pincer complex 19 and trigonal prismatic cages 21−22 were used as fluorescence sensors for nitroaromatic explosives owing to their large internal porosity and their π-electron rich nature. Scheme 3: Schematic representation of the formation of [3 + 2] self-assembled trigonal prismatic cage. CHAPTER 5 covers the syntheses of a few discrete metallamacrocycles using flexible imidazole/carboxylate based donors instead of much widely employed polypyridyl donors. The metal-ligand directed self-assembly of oxalato-bridged acceptor M8 and an imidazole-based tetratopic donor (L11; 1,2,4,5-tetrakis(imidazol-1-yl)benzene) in methanol afforded [2 + 1] self-assembled tetranuclear macrocycle 23. Conversely, the similar combination of L11 with 2,5-dihydroxy-1,4-benzoquinonato-bridged binuclear complex (M9) in 1:2 molar ratio in methanol resulted in an octanuclear cage 24. Both the complexes (23−24) were isolated as their triflate salts in high yields and were characterized by various spectroscopic methods including single crystal X-ray diffraction analysis. Scheme 4: Schematic representation of formation of an octanuclear incomplete Ru(II) open prism via ruthenium-oxygen coordination driven self-assembly. This chapter also explains the self-sorting of an unusual octanuclear incomplete prism [Ru8(η6-p-cymene)8(tma)2(μ-η4-C2O4)2(OMe)4](CF3SO3)2 (25) via ruthenium-oxygen coordination driven self-assembly of building block M8 and sodium benzene-1,3,5-tricarboxylate (L12) (Scheme 4). Electronic absorption study indicated that prism 25 exhibited a remarkable shape-selective binding affinity for 1,3,5-trihydroxybenzene (phluoroglucinol) via multiple hydrogen bonding interactions and such shape-selective binding was confirmed by single crystal X-ray diffraction analysis. (For figures pl see the abstract file)