title: Anomalous energy transfer dynamics due to torsional relaxation in a conjugated polymer.
abstract: In isolated conjugated polymers two explanations are in discussion for the redshift of the emission on a picosecond time scale-exciton energy transfer (EET) between conjugated segments along the chains and conformational changes of these segments themselves, i.e., torsional relaxation. In order to resolve this question we perform femtosecond time-resolved transient absorption measurements of the energy relaxation of poly[3-(2,5-dioctylphenyl)thiophene] in toluene solution. We show that torsional relaxation can be distinguished from EET by site-selectively exciting low-energy conjugated segments. We present a unified model that integrates EET and torsional dynamics. In particular, comparison to ultrafast depolarization measurements shows that torsional dynamics cannot be neglected when analyzing EET dynamics and furthermore reveals that the exciton extends itself by about 2 monomer units during torsional relaxation.
authors.affiliation: Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, UK. sw372@cam.ac.uk
authors.forename: Sebastian
authors.initials: S
authors.lastname: Westenhoff
authors.forename: Wichard J D
authors.initials: WJ
authors.lastname: Beenken
authors.forename: Richard H
authors.initials: RH
authors.lastname: Friend
authors.forename: Neil C
authors.initials: NC
authors.lastname: Greenham
authors.forename: Arkady
authors.initials: A
authors.lastname: Yartsev
authors.forename: Villy
authors.initials: V
authors.lastname: Sundström