title: Tuning the role of charge-transfer states in intramolecular singlet exciton fission through side-group engineering.
abstract: Understanding the mechanism of singlet exciton fission, in which a singlet exciton separates into a pair of triplet excitons, is crucial to the development of new chromophores for efficient fission-sensitized solar cells. The challenge of controlling molecular packing and energy levels in the solid state precludes clear determination of the singlet fission pathway. Here, we circumvent this difficulty by utilizing covalent dimers of pentacene with two types of side groups. We report rapid and efficient intramolecular singlet fission in both molecules, in one case via a virtual charge-transfer state and in the other via a distinct charge-transfer intermediate. The singlet fission pathway is governed by the energy gap between singlet and charge-transfer states, which change dynamically with molecular geometry but are primarily set by the side group. These results clearly establish the role of charge-transfer states in singlet fission and highlight the importance of solubilizing groups to optimize excited-state photophysics.
authors.affiliation: Cavendish Laboratory, J. J. Thomson Avenue, University of Cambridge, Cambridge CB3 0HE, UK.
authors.forename: Steven
authors.initials: S
authors.lastname: Lukman
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, and School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington 6010, New Zealand.
authors.forename: Kai
authors.initials: K
authors.lastname: Chen
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, and School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington 6010, New Zealand.
authors.forename: Justin M
authors.initials: JM
authors.lastname: Hodgkiss
authors.affiliation: Cavendish Laboratory, J. J. Thomson Avenue, University of Cambridge, Cambridge CB3 0HE, UK.
authors.forename: David H P
authors.initials: DHP
authors.lastname: Turban
authors.affiliation: Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
authors.forename: Nicholas D M
authors.initials: NDM
authors.lastname: Hine
authors.affiliation: Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Shaoqiang
authors.initials: S
authors.lastname: Dong
authors.affiliation: Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Jishan
authors.initials: J
authors.lastname: Wu
authors.affiliation: Cavendish Laboratory, J. J. Thomson Avenue, University of Cambridge, Cambridge CB3 0HE, UK.
authors.forename: Neil C
authors.initials: NC
authors.lastname: Greenham
authors.affiliation: Cavendish Laboratory, J. J. Thomson Avenue, University of Cambridge, Cambridge CB3 0HE, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Musser