title: Theory of Primary Photoexcitations in Donor-Acceptor Copolymers.
abstract: We present a generic theory of primary photoexcitations in low band gap donor-acceptor conjugated copolymers. Because of the combined effects of strong electron correlations and broken symmetry, there is considerable mixing between a charge-transfer exciton and an energetically proximate triplet-triplet state with an overall spin singlet. The triplet-triplet state, optically forbidden in homopolymers, is allowed in donor-acceptor copolymers. For an intermediate difference in electron affinities of the donor and the acceptor, the triplet-triplet state can have a stronger oscillator strength than the charge-transfer exciton. We discuss the possibility of intramolecular singlet fission from the triplet-triplet state, and how such fission can be detected experimentally.
authors.affiliation: Department of Physics, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Karan
authors.initials: K
authors.lastname: Aryanpour
authors.affiliation: Department of Physics, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Tirthankar
authors.initials: T
authors.lastname: Dutta
authors.affiliation: Department of Physics, University of Utah, Salt Lake City, Utah 84112, USA.
authors.forename: Uyen N V
authors.initials: UN
authors.lastname: Huynh
authors.affiliation: Department of Physics, University of Utah, Salt Lake City, Utah 84112, USA.
authors.forename: Zeev Valy
authors.initials: ZV
authors.lastname: Vardeny
authors.affiliation: Departments of Physics and Chemistry, University of Arizona, Tucson, Arizona 85721, USA.|College of Optical Sciences, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Sumit
authors.initials: S
authors.lastname: Mazumdar