Design, synthesis and study of photophysical properties of Re(I) and Ru(II) metal center organometallic complexes as dyes for harvesting sunlight.

Thumbnail Image
Issue Date
Komreddy, Venugopal R.
Rillema, D. Paul

Due to fascinating physical and photophysical properties, the Re(I) and Ru(II) metal complexes coordinated with small organic molecules, such as 2,2'-bipyridine, 1,10-phenanthroline, 2,2'-bipyrazine derivatives, are very promising class of compounds in Dye Sensitized Solar Cells (DSSC) or (Grätzel Cell) for solar energy conversion for next-generation photovoltaic devices. Herein, we successfully prepared a series of Re(I) complexes [Re(dcbpy)(CO)3X, Re(dcbpz)(CO)3X, Re(5-COOHphen)(CO)3Cl, [Re(phen)(CO)3(py-CH3COO)Re(phen)(CO)3]+ where X=Cl, Br, I, CN, SCN; dcbpy = 4-4'-dicarboxyl-2,2'-bipyridine; dcbpz = 5-5'-dicarboxyl-2,2'-bipyrazine; py-pyridine; 5-COOH-phen = 5-carboxyl-1,10-phenanthroline, dafo =4,5 diazo fluorene-9-one], rhenium (I) tricarbonyl complexes with bipyrazine derivatives, [Re(bpz)(CO)3Cl, Re(Me-bpz)(CO)3Cl, Re(Me2-bpz)(CO)3Cl, Re((COOCH3)2-bpz)CO)3Cl, Re(pypz)(CO)3Cl] and Ru(II) metal complexes where 2,2'-bipyrazine (bpz), 5-methyl-2,2'-bipyrazine (Me-bpz), 5,5'-dimethyl-2,2'-bipyrazine(Me2-bpz), dimethyl [2,2'-bipyrazine]-5,5'-dicarboxylate ((COOCH3)2-bpz), and 2-(pyridine-2-yl)pyrazine (pypz). A simple and efficient synthetic route is presented for the synthesis of a series of pyrazine compounds coupled with bromo derivatives, which lead formation of the C-C bridged dimers. The structural, physical and photophysical properties of these compounds were thoroughly investigated by various analytical techniques. The band at lower energy observed, which shows the typical metal-to-ligand charge transfer (MLCT) due to the d (PI) -> (PI) * transitions consistent with Re(I) dicarboxylate-bipyridine systems located in the 390 nm to 436 nm region. Very interestingly these compounds showed long lifetimes (τ > 50 ns) that can be attributed to anchoring dicarboxylate groups to TiO2 in DSSC. The optimum efficiency of these DSSC system is about 1%.

Table of Content
Thesis (Ph.D.)-- Wichita State University, College of Liberal Arts and Sciences, Dept. of Chemistry