Excitonic fs-luminescence rise in poly(phenylenevinylene), PPV

In the so-called molecular approach a realistic PPV chain is considered to be a collection of segmental subunits separated by a distribution of breaks, which arises by statistical disorder and predicts (i) a variation of conjugation lengths and (ii) a density of states (DOS) of localized S-1-levels. In this picture, the asymptotic optical dynamics is triggered by energy relaxation toward the low-energy tail states of the DOS and gives rise (i) to transient red shifts and (ii) to fs-luminescence patterns dependent on the spectral position of the luminescence window. In this work the delicate fs-interplay of both evolving and decaying luminescence photons caused by interference, due to inhomogeneous broadening (IHB), and the vibrational spacings in the Franck-Condon (FC) progression, has been studied. High-precision fs-luminescence rise-profiles have been probed at epsilon = 2.25 and 2.10 eV, respectively, that provide, for the first time, direct experimental evidence for the sequential dynamics of molecular hopping excitations in the segmental environment of PPV. (C) 1998 Elsevier Science B.V. All rights reserved.