Synthesis and Electronic Properties of Novel Donor-π-Acceptor-Type Functional Dyes with a Carbonyl-Bridged Bithiophene π-Spacer.

In this study, we synthesized novel donor-π-acceptor (D-π-A) functional dyes bearing a carbonyl-bridged bithiophene as a π-conjugated spacer and evaluated the absorption and fluorescence properties as well as the photostability. The developed dyes - possess an ,-diphenylaminophenyl electron donor unit and an electron acceptor unit such as a formyl group (), an (,-diethylthiobarbituryl)methylene moiety (), or a (3-dicyanomethylidene-1-indanon-2-yl)methylene moiety (). The absorption spectra of - in dichloromethane at room temperature showed absorption maxima at 569 nm, 631 nm, and 667 nm, respectively, and the stronger acceptors in and led to enhancement of the ICT character. In addition, and had a second absorption band in the visible region, showing panchromatic absorption properties. Electrochemical analyses of the developed dyes revealed that the carbonyl bridging group in the π-spacer contributes to stabilization of the frontier orbitals such as the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively), in comparison with the referential dyes bearing a dibutylmethylene-bridged bithiophene spacer, -. The HOMO/LUMO stabilization brought about high photostability in the doped poly(methyl methacrylate) film.