title: Direct S0→T Excitation of a Conjugated Polymer Repeat Unit: Unusual Spin-Forbidden Transitions Probed by Time-Resolved Electron Paramagnetic Resonance Spectroscopy.
abstract: A detailed understanding of the electronic structure of semiconducting polymers and their building blocks is essential to develop efficient materials for organic electronics. (Time-resolved) electron paramagnetic resonance (EPR) is particularly suited to address these questions, allowing one to directly detect paramagnetic states and to reveal their spin-multiplicity, besides its clearly superior resolution compared to optical methods. We present here evidence for a direct S0→T optical excitation of distinct triplet states in the repeat unit of a conjugated polymer used in organic photovoltaics. These states differ in their electronic structure from those populated via intersystem crossing from excited singlet states. This is an additional and so far unconsidered route to triplet states with potentially high impact on efficiency of organic electronic devices.
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Meyer
authors.affiliation: Optoelectronics Group, University of Cambridge , Cavendish Laboratory, Cambridge CB3 0HE, United Kingdom.
authors.forename: Florian
authors.initials: F
authors.lastname: Lombeck
authors.affiliation: Organic and Hybrid Electronics, Macromolecular Chemistry I, Universität Bayreuth , 95440 Bayreuth, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Huettner
authors.forename: Michael
authors.identifier: http://orcid.org/0000-0002-2377-5998
authors.initials: M
authors.lastname: Sommer
authors.forename: Till
authors.identifier: http://orcid.org/0000-0003-2913-0004
authors.initials: T
authors.lastname: Biskup