SYNTHESIS AND SPECTROELECTROCHEMICAL STUDIES OF ORGANIC DYES CONTAINING BIPHENYL OR FLUORENE

Abstract

New dipolar dyes featuring arylamine donors, fluorene or biphenyl conjugation and cyanoacetic acid, or didyanovinyl acceptor unit have been synthesized and characterized by spectral, optical, and electrochemical measurements. Absorption measurements indicate that the fluorene conjugation is beneficial for red shifting the charge transfer transition in the donor acceptor compounds. On the contrary the biphenyl linker leads to blue shifted hypochromic charge transfer transition. For a particular linker, the diphenylamine unit acts as an efficient donor when compared to the 1-naphthylphenylamine moiety. However, the red-shift observed in the absorption profile for the diphenylamine containing dyes are compensated by a reduction in the molar extinction coefficient, i.e., the naphthylamine derivatives are beneficial for increasing the molar extinction coefficient. Electrochemical investigations show that the fluorene based dyes are more redox stable than the corresponding biphenyl derivatives. Effects of deprotonation on the absorption maxima and redox potential of the cyanoacrylic-acid derivatives have been investigated by absorption and electrochemical measurements. These studies reveal a blue shift in absorption profile and cathodic shift for oxidation potential originating due to deprotonation of the dyes. The dye-sensitized solar cells fabricated using these dyes exhibit moderate to good efficiencies and the fluorene based dyes are better than the biphenyl analogs. Electron-withdrawing dicyanovinyl moiety dictates the absorption properties of the next class of dyes