Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 131, Issue 3, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.3177327
Keywords
charge exchange; excited states; excitons; oscillator strengths; photoluminescence; polymer blends; spectral line shift
Funding
- EPSRC for an Advanced Research
- Engineering and Physical Sciences Research Council [GR/S99075/02, GR/S99075/01] Funding Source: researchfish
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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 < x < 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.
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