Polarizability effects and energy transfer in quinquethiophene doped bithiophene and OPV films

Oligothiophene films (nT) and oligophenylenevinylene (OPV) nanoparticles are doped with quinquethiophene (5T) and investigated by steady-state and time-resolved fluorescence spectroscopy. In 2T films and highly ordered nanoparticles of unsubstituted OPVs, the fluorescence excitation spectra of 5T show vibrational structure, indicating a small distribution of ground-state geometries. The anisotropic effective polarizabilities of the host materials are obtained from the spectral positions of the fluorescence maxima of 5T. In the highly disordered nanoparticles of tert-butyl substituted OPVs, the vibrational structure of 5T excitation spectra is lost and the polarizability is isotropic. Efficient host–guest energy transfer is observed upon excitation of the host. The overall fluorescence quantum yield φF increases fivefold upon doping 2T films at doping levels of x5T=5×10−4. In OPV films, φF is almost independent of the doping level, probably due to the competition of energy and electron transfer between host and dopant.