title: Charge-transfer character of excitons in poly[2,7-(9,9-di-n-octylfluorene)(1-x)-co-4,7-(2,1,3-benzothiadiazole)(x)].
abstract: Quantum-chemical calculations performed on poly[2,7-(9,9-di-n-octylfluorene)(1-x)-co-4,7-(2,1,3-benzothiadiazole)(x)] copolymers (0 < or = x < or = 0.5) show that the lowest unoccupied molecular orbital is always highly localized on the benzothiadiazole (BT) units while the highest occupied molecular orbital is delocalized over the whole chain. Chains with a low BT content are characterized by a reduced oscillator strength of the lowest optical transition and by an increased charge-transfer character of the exciton. These results are supported experimentally by a blueshift of the lowest energy absorption band upon reduction in the BT ratio, lower photoluminescence efficiency, longer excited state lifetimes, and greater solvent dependence of the emission properties.
authors.affiliation: Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Winfield
authors.forename: Antoine
authors.initials: A
authors.lastname: Van Vooren
authors.forename: Moo-Jin
authors.initials: MJ
authors.lastname: Park
authors.forename: Do-Hoon
authors.initials: DH
authors.lastname: Hwang
authors.forename: Jérôme
authors.initials: J
authors.lastname: Cornil
authors.forename: Ji-Seon
authors.initials: JS
authors.lastname: Kim
authors.forename: Richard H
authors.initials: RH
authors.lastname: Friend
mesh_terms: D005449:Fluorenes / Q000737:chemistry*; D049449:Luminescence; D010777:Photochemistry; D011108:Polymers / Q000737:chemistry*; D011789:Quantum Theory; D013830:Thiadiazoles / Q000737:chemistry*
chemical_list: D005449:Fluorenes; D011108:Polymers; D013830:Thiadiazoles; C544674:poly(2,7-(9,9-di-n-octylfluorene)-co-4,7-(2,1,3-benzothiadiazole)); C015700:benzo-1,2,3-thiadiazole