Photoelectric conversion properties of four novel carboxylated hemicyanine dyes on TiO2 electrode

Four hemicyanine derivatives, 2-[4-(N-ethyl-N-carboxyethyl)amino] phenylethenyl-1,3,3-trimethyl-3H-indolium iodide (BIDC1), 2-[4-(N,N-dicarboxyethyl)amino]phenylethenyl-1,3,3-trimethyl-3H-indolium iodide (BIDC2), 2-[4-(N-ethyl-N-carboxyethyl)amino]phenylethenyl-1,1,3-trimethyl-1H-benz[e]indolium iodide (BIDC3) and 2-[4-(N,N-dicarboxyethyl)amino]phenylethenyl-1,1,3-trimethyl-1H-benz[e]indolium iodide (BIDC4), have been synthesized and identified with regard to their structures and electrochemical properties. It is found that the absorption spectra of BIDC3 and BIDC4 are broader than that of BIDC1 and BIDC2 because the former two have one more benzene ring on the electron acceptor side. Upon adsorption on a TiO2 electrode, the absorption spectra of the four BIDC dyes are all broadened forward to both red and blue sides compared with their respective spectra in ethanol solution. BIDC2 ( or BIDC4), bearing two carboxyl groups, has about two ( or three) times more adsorption and a broader absorption spectrum on TiO2 film compared with BIDC1 ( or BIDC3), which consequently leads to a better light-to-electricity conversion property. Among the four hemicyanine dyes, BIDC4 generated the highest photoelectric conversion yield of 4.9%, with a short-circuit photocurrent of 21.4 mA cm(-2), an open-circuit voltage of 424 mV, and a fill factor of 0.49 under irradiation with 90.0 mW cm(-2) white light from a Xe lamp.