title: Evolution of Nonmirror Image Fluorescence Spectra in Conjugated Polymers and Oligomers.
abstract: The nonmirror image relationship between absorption and fluorescence spectra of conjugated polymers contrasts with most organic chromophores and is widely considered a signature of interchromopohore energy funneling. We apply broad-band ultrafast fluorescence spectroscopy to resolve the evolution of fluorescence spectra for dilute solutions of conjugated oligothiophenes, where no energy transfer is possible. Fluorescence spectra evolve from a mirror image of absorption, which lacks vibronic structure, toward a spectrally narrower and vibronically structured species on the hundreds of femtosecond to early picosecond time scale. Our analysis of this fluorescence spectral evolution shows that a broad distribution of torsional conformers is driven to rapidly planarize in the excited state, including in solid films, which is supported by Raman spectroscopy and quantum chemical modeling. Our data have important implications for understanding different energy-transfer regimes that are delineated by structural relaxation.
authors.affiliation: School of Chemical and Physical Sciences, Victoria University of Wellington , Wellington 6140, New Zealand.|MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand.
authors.forename: Joseph K
authors.initials: JK
authors.lastname: Gallaher
authors.affiliation: School of Chemical and Physical Sciences, Victoria University of Wellington , Wellington 6140, New Zealand.|MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand.
authors.forename: Kai
authors.initials: K
authors.lastname: Chen
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand.|Department of Chemistry, University of Otago , Dunedin 9016, New Zealand.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Huff
authors.affiliation: School of Chemical and Physical Sciences, Victoria University of Wellington , Wellington 6140, New Zealand.|MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand.
authors.forename: Shyamal K K
authors.initials: SK
authors.lastname: Prasad
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand.|Department of Chemistry, University of Otago , Dunedin 9016, New Zealand.
authors.forename: Keith C
authors.initials: KC
authors.lastname: Gordon
authors.affiliation: School of Chemical and Physical Sciences, Victoria University of Wellington , Wellington 6140, New Zealand.|MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand.
authors.forename: Justin M
authors.initials: JM
authors.lastname: Hodgkiss