title: Conformational disorder and ultrafast exciton relaxation in PPV-family conjugated polymers.
abstract: We report combined experimental and theoretical studies of excitation relaxation in poly[2-methoxy,5-(2'-ethyl-hexoxy)-1,4-phenylenevinylene] (MEH-PPV), oligophenylenevinylene (OPV) molecules of varying length, and model PPV chains. We build on the paradigm that the basic characteristics of conjugated polymers are decided by conformational subunits defined by conjugation breaks caused by torsional disorder along the chain. The calculations reported here indicate that for conjugated polymers like those in the PPV family, these conformational subunits electronically couple to neighboring subunits, forming subtly delocalized collective states of nanoscale excitons that determine the polymer optical properties. We find that relaxation among these exciton states can lead to a decay of anisotropy on ultrafast time scales. Unlike in Forster energy transfer, the exciton does not necessarily translate over a large distance. Nonetheless, the disorder in the polymer chain means that even small changes in the exciton size or location has a significant effect on the relaxation pathway and therefore the anisotropy decay.
authors.affiliation: Lash-Miller Chemical Laboratories, Institute for Optical Sciences and Centre for Quantum Information and Quantum Control, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6 Canada.
authors.forename: Tieneke E
authors.initials: TE
authors.lastname: Dykstra
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Hennebicq
authors.forename: David
authors.initials: D
authors.lastname: Beljonne
authors.forename: Johannes
authors.initials: J
authors.lastname: Gierschner
authors.forename: Gil
authors.initials: G
authors.lastname: Claudio
authors.forename: Eric R
authors.initials: ER
authors.lastname: Bittner
authors.forename: Jasper
authors.initials: J
authors.lastname: Knoester
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Scholes