SEQUENTIAL FEMTOSECOND OPTICAL-DYNAMICS IN POLY(PHENYLENEVINYLENE), PPV

In the weak coupling, molecular site approach poly(phenylene-vinylene) (PPV) is modeled in terms of conformational breaks that statistically interrupt the x-conjugation length and give rise (i) to segmental sub units, distributed in self-energy and (ii) to a density-of-states (DOS ) of S-1 levels upon electronic excitation. For two different, spectra l positions of the luminescence probe window, it is demonstrated that intra-DOS cascading, i.e. the femtosecond population transfer from hig h-energy tail-states to low-energy wing states carl be probed in real time by means of luminescence up-conversion measurements. Parametrized , biexponential profiles, i.e. a fs decay (tau(1) approximate to 350 f s) and a complementary pattern containing a significant fs rise (tau(1 ) approximate to 310 fs) have been found for the luminescence evolutio ns at 2.7 and 2.25 eV, respectively, that directly trace the sequentia l dynamics of optical spectral diffusion. A many-body treatment based upon a combined MC and a Pauli-master equation analysis has yielded qu ite satisfactory results in favor of the distributed nature of the opt ical relaxation process.