Subpicosecond study of excitons in a phenylenevinylene conjugated polymer:exciton-exciton interactions and infrared photoinduced absorption features

We present a study of the fundamental photoexcitations in a phenylenevinyle ne conjugated polymer from the visible to the mid-infrared (IR) using polar ized subpicosecond transient absorption (TA) spectroscopy. From 0.5 to roug hly 1.3 eV we find that features due to singlet intrachain excitons dominat e the photoinduced absorption. Two peaks are apparent in the spectrum: one near 0.5 eV and the other at similar to1.1 eV. In the regime of high excita tion densities (> 10(19) cm(-3)), we find evidence of exciton-exciton inter actions leading to exciton hopping between different chains or segments of the polymer. (C) 2000 Published by Elsevier Science B.V.