Synthesis and photophysical characterization of re(i) and ru(ii) complexes: potential optical limiting materials and light harvesting systems
Description
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 Ï€-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).