Ruthenium(II) complex based on 4,4′-di(p-methylphenyl)-2,2′-bipyridine: Synthesis and photoelectrochemical properties

4,4′-Di(p-methylphenyl)-2,2′-bipyridine was conveniently synthesized from 2-bromopyridine through halogen-dance reaction, selective Kharash coupling and homo coupling of 2-bromopyridine derivative. Its corresponding ruthenium complex: cis-N,N-4,4′-di(p-methylphenyl)-2,2′-bipyridine-N,N-4,4′-dicarboxy-2,2′-bipyrine-N,N-dithiocyanato ruthenium(II) (dye-1) was also obtained and characterized by element analysis, MALDI-TOF MS and H NMR spectra. Compared with cis-N,N-2,2′-bipyridine-N,N-4,4′-dicarboxy-2,2′-bipyridine-N,N-dithiocyanato ruthenium(II), dye-1 displayed red-shifted MLCT absorptions and enhanced molar extinction coefficients for its rigid π-conjugation. As a result, dye-1 sensitized nanocrystalline TiO2 electrode gave higher short circuit photocurrent density of 12.6 mA cm−2 and overall photo-to-electric conversion efficiency of 5.5% (AM1.5, 75 mW cm−2).