Fluorescence dynamics of phenyl-substituted polyphenylenevinylene-trinitrofluorenone blend systems

Steady state as well as time-resolved fluorescence of phenyl-substituted polyphenylenevinylene (PhPPV), both in solution and in form of spin-coated films has been measured. In solution the fluorescence decays exponentially with a 1/e decay time of similar to700 ps, whereas the 1/e decay in the film is similar to400 ps and the decay approaches a stretched exponential with an exponent of beta=0.65. Doping the film with various amounts of trinitrofluorenone (TNF) shortens the decay time without changing the form of the Kohlrausch-Williams-Watts decay law. This is a signature of exciton dissociation in a random polymer matrix through electron transfer to TNF. The data analysis shows that "neat" PhPPV contains a concentration of less than or equal to 0.04 wt. % of unidentified electron scavengers. A hypsochromic shift of the cw fluorescence spectra in doped films is interpreted in terms of increasingly frustrated spectral relaxation of singlet excitations within the inhomogeneously broadened distribution of hopping states. (C) 2002 American Institute of Physics.