Electrogenerated chemiluminescence (ECL) studies were performed on several interesting compounds. A series of BODIPY derivatives was examined to understand the structural effects on the electrochemical, spectroscopic, and ECL behavior. Stable electrochemistry and high fluorescence in the green to the red regions were observed. PB, MCPB, DCPB and PM580 produced intense ECL, strong enough to be seen with the naked eye in a lighted room. Unlike MCPB and DCPB, PB produced the multiple ECL peaks. Totally blocked BODIPY compound showed the improvement of fluorescence and ECL quantum yield due to the stability of radicals. Strong signal of EPR data during the oxidative electrolysis was obtained by simultaneous electrochemical-electron paramagnetic resonance technique with home-made cell. Several new antrhacene derivatives such as a variety of 2- and 4-fold anthracene-functionalized tetraarylbimesityls and a series of 9-naphthylanthracene based dimer and trimer were studied. They showed one wave on the oxidation and reduction because of a sequence, two or more electron transfers during the annihilation of the radical ions. Depended on the structure, some of them exhibited excimer formation on ECL spectra. Azide-BTA compound which consists of two triphenylamine and 2,1,3-benzothiadiazole groups at the ends bridged by a fluorene moiety was synthesized and examined. The compound is a newly synthesized D-A-[pi]-A-D molecule which had reversibility upon electrochemical oxidation and reduction, and also showed intense red fluorescence and stable red ECL emission. Using a simple reprecipitation method, well-dispersed and spherical organic nanoparticles of Azide-BTA and 9-naphthylanthracene based dimer were prepared in an aqueous solution. Controlling the preparation condition, the size of nanoparticles can be minimized to 15 nm. Especially we prepared the organic nanoparticles of 9-naphthylanthracene based dimer dispersed in organic solvent, MeCN, one of the preferred solvents for electrochemical studies and ECL. / text

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<p>This thesis is divided into four parts with organic chromophores for dye sensitized solar cells as the common feature and an introduction with general concepts of the dye sensitized solar cells.</p><p>The first part of the thesis describes the development of an efficient organic chromophore for dye sensitized solar cells. The chromophore consists of a triphenylamine moiety as an electron donor, a conjugated linker with a thiophene moiety and cyanoacrylic acid as an electron acceptor and anchoring group. During this work a strategy to obtain an efficient sensitizer was developed. Alternating the donor, linker or acceptor moieties independently, would give us the tool to tune the HOMO and LUMO energy levels of the chromophores. The following parts of this thesis regard this development strategy.</p><p>The second part describes the contributions to the HOMO and LUMO energy levels when alternating the linker moiety. By varying the linker the HOMO and LUMO energy levels was indeed shifted. Unexpected effects of the solar cell performances when increasing the linker length were revealed, however.</p><p>The third part describes the investigation of an alternative acceptor group, rhodanine-3-acetic acid, in combination with different linker lengths. The HOMO and LUMO energy level tuning was once again successfully shifted. The poor electronic coupling of the acceptor group to the semiconductor surface proved to be a problem for the overall efficiency of the solar cell, however.</p><p>The fourth part describes the contributions from different donor groups to the HOMO and LUMO energy levels and has so far been the most successful in terms of reaching high efficiencies in the solar cell. A top overall efficiency of 7.1 % was achieved.</p>

The synthesis and comprehensive characterization of diamine and diimine derivatives of thioindigo are reported. X-ray crystal structures demonstrate a planar structure for the diimine derivatives and a twisted conformation for the diamines. The diamine compounds absorb in the UV (λmax 324 nm - 328 nm), and exhibit moderate fluorescence (ΦF = 0.25, 0.045). A transient triplet state is observed in laser flash photolysis (LFP) experiments, with lifetimes an order of magnitude longer than those of the triplet state of thioindigo. The diimine compounds absorb at longer wavelengths than the diamines (λmax 495 nm - 510 nm), but are still slightly blue-shifted from thioindigo. The diimines have molar extinction coefficients 17 – 70% higher than thioindigo. The diimine compounds are not emissive, and LFP studies show transient species with microsecond lifetimes. The transient absorption spectra and quenching experiments of the diimines are consistent with trans-cis isomerisation about the central double bond. Mono- and diruthenium hexafluoroacetylacetonate (hfac) complexes of thioindigo-N,Nʹ-diphenyldiimine have been prepared. The monoruthenium complex was isolated as a racemic mixture and the diruthenium complexes were isolated as the meso (ΔΛ) and rac (ΔΔ and ΛΛ) diastereomers. Extensive structural characterization of the compounds revealed intrinsic diastereomeric differences in the X-ray crystal structures, cyclic voltammograms, and NMR spectra. Variable temperature NMR experiments demonstrated that the rac diastereomer undergoes conformational exchange with a rate constant of 8700 sec-1 at 298 K, a behavior that is not observed in the meso diastereomer. Ground state optical properties of the complexes were examined, showing that all the complexes possess metal-to-ligand charge transfer (MLCT) absorption bands in the near-infrared (λmax 689 nm – 783 nm). The compounds do not display photoluminescence in room temperature solution-phase experiments or in experiments at 77 K. Ultrafast transient absorption spectroscopy measurements revealed excited states with picosecond lifetimes. Unexpectedly, the transient absorption measurements revealed differences in the transient spectra and disparate time constants for the excited state decay of the diastereomers, which are linked to the conformational changes observed in the NMR experiments. Investigations into the synthesis of azaDIMEs and azaDicarbazolyls are described. Examination of the Buchwald-Hartwig amination produced reaction conditions that enabled preparation of amino-diindoles. Oxidation of the amino-diindoles to azaDIMEs was complicated by concomitant oligomerization of the substrates. Substitution of the reactive positions of the amino-diindole afforded increased stability towards oxidative oligomerization. Scalable synthetic routes to azaDicarbazolyl precursors were identified and optimized, and preparation of amino and azaDicarbazolyl compounds was explored. / Graduate / 2021-04-18

This thesis is divided into four parts with organic chromophores for dye sensitized solar cells as the common feature and an introduction with general concepts of the dye sensitized solar cells. The first part of the thesis describes the development of an efficient organic chromophore for dye sensitized solar cells. The chromophore consists of a triphenylamine moiety as an electron donor, a conjugated linker with a thiophene moiety and cyanoacrylic acid as an electron acceptor and anchoring group. During this work a strategy to obtain an efficient sensitizer was developed. Alternating the donor, linker or acceptor moieties independently, would give us the tool to tune the HOMO and LUMO energy levels of the chromophores. The following parts of this thesis regard this development strategy. The second part describes the contributions to the HOMO and LUMO energy levels when alternating the linker moiety. By varying the linker the HOMO and LUMO energy levels was indeed shifted. Unexpected effects of the solar cell performances when increasing the linker length were revealed, however. The third part describes the investigation of an alternative acceptor group, rhodanine-3-acetic acid, in combination with different linker lengths. The HOMO and LUMO energy level tuning was once again successfully shifted. The poor electronic coupling of the acceptor group to the semiconductor surface proved to be a problem for the overall efficiency of the solar cell, however. The fourth part describes the contributions from different donor groups to the HOMO and LUMO energy levels and has so far been the most successful in terms of reaching high efficiencies in the solar cell. A top overall efficiency of 7.1 % was achieved. / QC 20101108

Artificial photosynthesis, for the purpose of converting solar energy into fuel, is one of the most viable and promising alternative approaches to solve the current global energy and environmental issues. Among the challenges faced in artificial photosynthesis is in building photosystems that can effectively and efficiently perform light absorption and charge separation in broad-band capturing donor-acceptor systems. While having a broad-band capturing antenna system that can harness incoming photons is crucial, another equally important task is to successfully couple the antenna system, while maintaining its optical properties, to an energy or electron acceptor which serves as the reaction center for the generation of charged species of useful potential energy. The stored potential energy will be utilized in different applications such as driving electrons in solar cells or in splitting water for the generation of fuel. Hence, the particular endeavor of this thesis is to study and synthesize molecular/supramolecular systems with wide-band capturing capabilities to generate long-lived charge separated states. The sensitizer used in building these systems in the present study is 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, for short, BF2 chelated Azaboron dipyrromenthene or AzaBODIPY. A handful of novel donor-acceptor systems based on AzaBODIPY have been successfully designed, synthesized and their photochemistry have been investigated using various techniques. In these systems, Azabodipy has been covalently attached to several donors like porphyrin, bodipy, subphthalocyanine, phenothiazine, ferrocene, bithiophene and effectively coupled to an electron acceptor, C60. These systems have been fully characterized by NMR, Mass, optical absorption and emission, X-ray crystallographic, computational, electrochemical, and photochemical studies. It has been possible to demonstrate occurrence of efficient electron and energy transfer events and long-lived charge separated states upon photoexcitation in these model compounds. By changing the arrangements of the donor and acceptor entities, it has also been possible to show directional, through-space and through-bond electron transfer processes. The present study brings out the importance of utilizing near-IR sensitizers in building solar energy harvesting model systems.