The electronic states of polyfluorene copolymers with alternating donor-acceptor units.
We calculate the electronic states of the low bandgap polyfluorene-based copolymer DiO-PFDTBT, which consists of alternating 9,9-dioctyl-9H-fluorene and 4,7-di-thiophen-2-ylbenzo[1,2,5]thiadiazole (TBT) units, and compare with the steady-state absorption, emission, and excitation spectrum. Using the semiempirical quantum-chemical (ZINDO) method we can assign the characteristic bands of the "camel-back" absorption spectrum to one charge transfer state at lower energy localized on the TBT unit, and one delocalized excitonic state at higher energy corresponding to the pi-conjugated electron system. Additional "dark" charge transfer states in the gap between these bands have been revealed. Calculations are also made on the red light emitting polyfluorene-based copolymer poly(fluorene-co-benzothiadiazole) (F8BT), which contains benzo[1,2,5]thiadiazole instead of TBT. The nature of the electronic states in F8BT and DiO-PFDTBT are found to be qualitatively the same.
Jespersen
Kim G
KG
Department of Chemical Physics, Lund University, Kemicentrum, Getingevägen 60, SE-22100 Lund, Sweden.
Beenken
Wichard J D
WJ
Zaushitsyn
Yuri
Y
Yartsev
Arkady
A
Andersson
Mats
M
Pullerits
Tõnu
T
Sundström
Villy
V