Fluorescence dynamics of phenyl-substituted polyphenylenevinylene–trinitrofluorenone blend systems

Abstract

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 ∼700 ps, whereas the 1/e decay in the film is ∼400 ps and the decay approaches a stretched exponential with an exponent of β=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 ⩽ 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.