The overall efficiency of photovoltaics is dictated by processes occurring within it. These processes include exciton formation, diffusion, dissociation and charge collection. This dissertation will focus around the fundamental issue of charge collection. In organic photovoltaics (OPVs) the rate of charge injection is dominated by the interaction between dissimilar materials, usually organic compound interacting with inorganic ones. In order to improve this rate of injection and, by direct consequence the efficiency of this process, fundamental knowledge of this organic-inorganic interface must be gained. In this work the focus will reside solely on creating molecules capable of probing the interface between the indium tin oxide (ITO) and the donor layer. At this interface, the usual charge transfer being transferred is the hole. Chapters 2 and 3 detail the synthesis and photophysical characterization of porphyrin-perylene diimide (Por-PDI) and porphyrin-fullerene (Por-C₆₀) molecular dyads. The idea behind these moieties is that covalent attachment of these species to ITO should lead to a robust ohmic contact. Since these molecular dyads are capable of producing charge-separated states after photoexcitation, they should have the capacity to produce a radical-cation in close proximity to the ITO. This will translate to a capacity for probing the dynamics of the hole injection at this interface. Studies performed demonstrate that in fact these dyads are capable of producing a charge-separated state upon photo-excitation. The lifetimes of these states were determine to be 35 ps and 3 ns for the Por-PDI and Por-C₆₀ respectively. Chapter 4 takes a different turn. It is focused on the application and extension of a solvent-free synthesis of metallated phthalocyanines (Pcs). Shown in chapter 4 is the synthesis of a series of metallated Pcs using various transition metals and group 3 elements. Photophysical and electrochemical investigation of these materials shows that they have near-infrared absorption and relative high HOMO levels making them potential candidates for OPV applications. In addition, they displayed non-linear optical behavior due to their highly polarizable pi-systems and the presence of axial susbtituents. Finally Chapter 5 describes the synthesis and characterization of porphyrin possessing rigid linkers. This chapter also shows the further directions in which the various ideas presented in this work could be driven.

This dissertation can be divided into two parts project goals. The first one is the synthesis of rhenium (Re) complexes which are potential reverse saturable absorber (RSA) materials. The second one is the polymerization of ruthenium (Ru) polypyridyl monomers to have an oligomer ensemble for solar light harvesting purposes. THE FIRST part starts with an introduction to optical limiting materials (OLM) (chapter 1). The main discussion in chapter 4 is about the photophysical properties and energy-transfer reactions for three series of facial Re(I) tri-carbonyl complexes. The complexes are of the general type fac-[Re(CO)3(N-N)Cl], where Cl is the chloride and N-N are novel mono functionalized aryl-oligo(p-phenylene-vinylene) bipyridine (bpy) ligands. These series is as a result of changing the aryl group of the ligands to either anthracene or pyrene, and di-alkoxy attachments of phenyl ring in anthracene bipyridine ligands. The synthesis of the bpy ligands involved attaching various aryls by utilizing successive multi-step Wittig-Horner reactions (chapter 2). The ligands were later reacted with Re pentacarbonyl chloride to obtain the complexes. Chromium complexes synthesis is also included (chapter 3). The characterization involved 1H NMR, ESI-MS and elemental analysis. There is also another set of ligands where the aryl group is di-methylaminophenyl where the solvatochromic emission properties of the ligands were studied but were not coordinated to metals. The excited-state properties using both the nanosecond (ns) and picosecond (ps) time resolved transient absorption (TA) of Re(I) complexes shows strong positive excited-state absorption signals in 500-800 nm range. From the TA (ps) and time-resolved infrared of the carbonyl region, the excited state forms instantaneously after excitation. Their observed lifetimes are relatively long (2 μs-40 μs range) and they increase as the phenylene-vinylene linker increases. The excited state triplet energies values for the complexes were obtained experimentally using energy transfer method from the simple Sandros relation. They decreases as the π-conjugated phenylene-vinylene linker decreases, this is because the extended backbone bridge serves to lower the energy of the triplet excited state. Lastly, the Re(I) complexes triplet-triplet molar extinction coefficients(δex) were measured by energy transfer to a standard method and their ratios to the ground state molar absorptivity(δg ) are all (δex/δg ≥40) at 530nm which make them potential candidates for RSA. THE SECOND part involves RAFT polymerization of two new acrylamide functionalized Ru(II) polypyridyl monomers. Photoinduced electron transfer reactions for the obtained Ru oligomers and complexes were done using 10-methylphenothiazine (MPT) quencher (chapter 8). The synthesized acrylamide functionalized bipyridine ligand (chapter 6) was reacted with complex precursors cis-[Ru(L)2Cl2] where the ligand (L) is either 2,2’- bipyridine or biquinoline (chapter 7). The obtained Ru(II) photosensitizers acts as energy donating and accepting respectively. The attachment of these Ru complexes to oligomer backbone as side chains is by a C11 alkyl linker. 1H NMR, UV-Vis spectroscopy, and differential pulse voltammetry (DPV) were used to characterize the ligand, monomers and oligomers. The excited state REDOX potentials were determined using the cyclic voltammetry (CV) values and steady state emission values converted to electron volt (eV). Lastly, the TAs (ns) obtained in the presence of MPT electron donating quencher was in agreement with the ones calculated/ predicted from spectroelectrochemistry. These efforts are toward the goal of making a panchromatic solar light collector in the visible region (chapter 5). / acase@tulane.edu