Charge-transfer character of excitons in poly[2,7-(9,9-di-n-octylfluorene)(1-x)-co-4,7-(2,1,3-benzothiadiazole)(x)].
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.
Winfield
Jessica M
JM
Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
Van Vooren
Antoine
A
Park
Moo-Jin
MJ
Hwang
Do-Hoon
DH
Cornil
Jérôme
J
Kim
Ji-Seon
JS
Friend
Richard H
RH
D005449:Fluorenes / Q000737:chemistry*; D049449:Luminescence; D010777:Photochemistry; D011108:Polymers / Q000737:chemistry*; D011789:Quantum Theory; D013830:Thiadiazoles / Q000737:chemistry*
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