Femtosecond site-selective probing of energy relaxing excitons in poly(phenylenevinylene): Luminescence dynamics and lifetime spectra

Exciton relaxation in poly(phenylenevinylene), PPV, has been probed by femtosecond luminescence-up-conversion. We report on excitonic luminescence profiles that depend on the spectral position of the detection window (e=2.7,2.6,2.5, and 2.4 eV, respectively). In an attempt to reveal the transient steps implied in fs relaxation, we present a quantitative forward reconvolution fit procedure that is based on a microscopic incoherent transport model, including diagonal disorder, dipolar intersite coupling, and a density-of-states (DOS) of molecular site excitations. Special emphasis has been placed (i) on the analysis of luminescence lifetime distributions 〈φ(τ;e,τ0)〉 which directly map out the spectra of hopping modes of energy-cascading neutral excitations, and (ii) on the rigorous evaluation of (radiationless) transfer population from high-energy subensembles to low-energy tail states of the DOS. We quantitatively show that the absence of significant rise terms in the S0ν=0←S1ν=0 luminescence transition ...

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