Nanolayered Heterojunctions of Donor and Acceptor Conjugated Polymers of Interest in Light Emitting and Photovoltaic Devices: Photoinduced Electron Transfer at Polythiophene/Polyquinoline Interfaces

Abstract

Four new nanolayered heterojunctions of electron-donating poly(3-hexylthiophene-2,5-diyl) and poly(3-octylthiophene-2,5-diyl) with two electron-accepting polyquinolines have been prepared, and the photophysical processes occurring at the polymer/polymer interfaces were investigated by photoluminescence (PL) spectroscopy and picosecond time-resolved PL decay dynamics. Observed nearly complete quenching of the steady-state photoluminescence and a factor of 160 shortening of the fluorescence lifetime of the polyquinolines suggested photoinduced electron transfer from polythiophene to polyquinoline at the polyquinoline/polythiophene interfaces. A new, weak and red shifted, emission band centered at 630 nm and reduced lifetimes show the formation of intermolecular exciplexes at the polyquinoline/polythiophene interfaces. This is the first example of intermolecular exciplex formation between two π-conjugated polymers. Exciton diffusion lengths in the polyquinolines were estimated to be 17−22 nm. These results suggest that nanolayered polythiophene/polyquinoline heterojunctions are promising new material systems for the development of photovoltaic devices and for model studies of the photophysics of multicomponent conjugated polymers.