Quantum chemical calculations have been used to model dye-sensitized nanostructured titanium dioxide systems that can be used in solar cells for solar energy to electricity conversion. Structural, electronic and spectral properties of isolated dyes and both bare and dye-sensitized TiO2 have been calculated with density functional theory, providing detailed information about both the separate parts and the dye-TiO2 interface. The connection between the geometry, the ligand field splitting and the lifetime of the triplet metal-to-ligand charge transfer (MLCT) excited state has been explored for a series of ruthenium polypyridyl dyes. Moreover, the relative energetics of MLCT and metal centered triplet excited states have been studied for a number of such systems. It was found that small alterations of the polypyridyl ligands can result in significant changes in ligand field splitting and in the energetics of the triplet states. Attachment of the dyes to the TiO2 surface is achieved via anchor and spacer groups. The influence of such groups on various properties of the dye and their ability to act as mediators of photo-induced surface electron transfer has been studied. Delocalization of the lowest unoccupied dye orbital onto the spacer and/or anchor group indicates that certain unsaturated groups can mediate electron transfer. With a combination of methods that enables efficient computations and a scheme for construction of metal oxide clusters, chemical models for bare TiO2 nanocrystals in the 1-2 nm size range have been developed. The electronic structures show well-developed band structures with essentially no electronic band gap defect states. Atomistic models of the interface between TiO2 nanocrystals and Ru(II)-bis-terpyridine dyes, the so-called N3 dye as well as perylene dyes are reported. Electronic coupling strengths, which provide estimates for the electron injection times, are extracted from the interfacial electronic structure and the lowest electronic excitations are calculated.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

In this thesis, a first-principles methodology to investigate the impact of electron-phonon interactions on the charge-carrier mobilities in organic molecular crystals has been developed. Well-known organic materials such as oligoacene and oligothienoacene derivatives were studied in detail. The nature of the intramolecular vibronic coupling in oligoacenes and oligothienoacenes was studied using an approach that combines high-resolution gas-phase photo-electron spectroscopy measurements with first-principles quantum-mechanical calculations. The electron interactions with optical phonons in oligoacene single crystals were investigated using both density functional theory and empirical force field methods. The low-frequency optical modes are found to play a significant role in dictating the temperature dependence of the charge-transport properties in the oligoacene crystals. The microscopic charge-transport parameters in the pentathienoacene, 1,4-diiodobenzene, and 2,6-diiodo-dithieno[3,2-<i>b</i>:2',3'-<i>d</i>]thiophene crystals were also investigated. It was found that the intrinsic charge transport properties in the pentathienoacene crystal might be higher than that in two benchmark high-mobility organic crystals, i.e., pentacene and sexithienyl. For 1,4-diiodobenzene crystal, a detailed quantum-mechanical study indicated that its high mobility is primarily associated with the iodine atoms. In the 2,6-diiododithieno[3,2-<i>b</i>:2',3'-<i>d</i>]thiophene crystal, the main source of electronic interactions were found along the π-stacking direction. For negatively charged carriers, the halogen-functionalized molecular crystals show a very large polaron binding energy, which suggests significantly low charge-transport mobility for electrons.

Chapter 1.<br />1-Ethynyl-2-phenyltetramethyldisilanes HCºCSiMe2SiMe2C6H4-p-X [X = NMe2(1.1), Me (1.2), H (1.3), Br (1.4), CF3 (1.5)] are accessible from ClSiMe2SiMe2Cl, BrMgC6H4X and HCºCMgBr in a two step Grignard reaction. The crystal structure of 1.1 as determined by single crystal X-ray crystallography exhibits a nearly planar PhNMe2 moiety and an unusual gauche array of the phenyl and the acetylene group with respect to rotation around the Si-Si-bond. Full geometry optimization (B3LYP/6- 31+G**) of the gas phase structures of 1.1 and 1.3 affords minima for the gauche and the trans rotational isomers, both being very close in energy with a rotational barrier of only 3 – 5 kJ/mol. Experimental and calculated (time-dependent DFT B3LYP/TZVP) UV absorption data of 1.1 – 1.5 show pronounced electronic interactions of the HCºC- and the C6H4X p-systems with the central Si-Si bond.<br /><br />Chapter 2.<br />A family of [( 5-Cp*)Ru( 6-arene)]+ (Cp* = C5Me5) sandwich complexes of 1- and 1,4-substituted phenyl and naphthyl systems are described along with the regioselectivities of the reactions under various conditions. Finally, the (h 5-Cp*) Ru+ arenophile was found to act as a gate to the flow of electrons between para-substituted termini. When it is complexed onto the phenyl or A naphthyl ring, the gate is closed. On the contrary, when it is complexed onto the B naphthyl ring, the gate is open.<br /><br />Chapter 3.<br />Regioselective complexation reactions of the organoiron acetylide derivatives (h 2- dppe)(h 5-Cp*)Fe-C C-Ar (Ar = phenyl, 1-naphthyl; dppe = 1,2- bis(diphenylphosphino)ethane) with [(h 5-Cp*Ru(CH3CN)3][PF6] to afford heterobimetallic complexes formulated as [(h 2-dppe)(h 5-Cp*)Fe-C C-{(h 6-Ar)Ru(h 5- Cp*)}][PF6], were achieved. In the case of the FeII-RuII 1-naphthyl derivative, the (h 5-Cp*)Ru+ arenophile was complexed both onto the substituted ring and free rings of the acetylide 1-naphthyl linker. The first redox-driven h 6-h 6 inter-ring haptotropic migration of the (h 5-Cp*)Ru+ moeity was shown to occur. Crystal structures of all of the seven new iron acetylenes were resolved, including both haptotropomers of the naphthyl compound.<br /><br />Chapter 4.<br />The diorganoiron [{(h2-dpppe)(h5-Cp*)Fe-CC-}2(1,4-naphthyl)] (4.12) was synthesized in good yield in two steps via the vinylidene, and oxidation led to the mixed valence (MV) and iron(III)-iron(III) species in good to excellent yields. This exhaustive empirical study on the family of complexes 4.12[PF6]n (n = 0,1,2) includes a crystal structure for the case in which n = 2. This work clearly establishes good electronic and magnetic communication between the iron centers across the bis(ethynyl)naphthalene bridge. All empirical measurements of these naphthyl compounds reveal that their properties fall between those of known phenyl and anthracenyl derivatives. In some cases, the naphthyl derivative behaves as an average of the phenyl and anthracenyl complexes. For example, the comproportionation constant of the naphthyl species falls at the midpoint between those for the phenyl and anthracenyl compounds. The same is true for the UV absorption maxima in all three oxidation states (Fe[II]- Fe[II], MV, and Fe[III]- Fe[III]). The large electronic (2043 cm-1) and magnetic (-526 cm-1) coupling constants were determined via NIR spectroscopy and SQUID magnetometry, respectively. As for the heterotrinuclear species, the iron(II) acetylene, 4.14B[PF6] [{Cp*(dppe)Fe-C C}2-(h 6 – [1,4-napthyl])RuCp*](PF6), [Cp* = h 5 - C5Me5; Fe = FeII] was prepared in high yields with an adapted, regioselective synthesis via the trinuclear vinylidene. Complete characterization, including a crystal structure, of this sandwich complex reveals that the arenophile perturbs the organoiron ligand more in the bis(iron) than in the previously reported mono(iron) case.