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

Abstract

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 ε = 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.