Spectroscopic studies of oligodiacetylenes in solution and polymer film

Abstract

The photophysical properties of a series of monomeric, dimeric and trimeric oligodiacetylenes (ODAs; oligoenynes) bearing trimethylsilyl, t-butyl and n-octyl end-capping substituents were studied in solution and in a polymer film. Emission studies show a significant emission of oligodiacetylenes in solution, which increased with increased conjugation. This is remarkable given the near absence of fluorescence in oligoenes of similar length (e.g. hexatriene) and polydiacetylenes (PDAs), which constitute the conjugation limit. A large Stokes shift was observed, and shown to originate from an energy difference between the Franck-Condon excited state and the fluorescent state. From near-identical angles obtained for the absorption and emission dipoles it was concluded that the overall geometry of ODAs does not significantly change upon electronic transition.