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Electronic Properties of Two Series of Blue-Emitting Conjugated Oligomers and Polymers Based on Cyanostilbene: A Quantum Chemistry Study
- Source :
- Chinese Journal of Chemistry. 25:1491-1498
- Publication Year :
- 2007
- Publisher :
- Wiley, 2007.
-
Abstract
- One of the drawbacks of the electroluminescence (EL) polymers is that they are usually much better at accepting and transporting holes than electrons due to their inherent richness of π-electrons. One approach improving electron injection and transport in conjugated polymers is to incorporate moieties with high electron affinities. In this theoretical work, to gain an insight into the chemical structure-property relationships was aimed by controllable modification of the main chain structures. Two cyanovinylene derivatives with 2,7-fluorenylene and p-phenylene moieties in the main chains, namely, poly{(2,5-dimethoxy-p-phenylene-1,4-ylene)-alt-[1,2-bis(p-phenylene)-1- cyanovinylene]} (PPhCN) and poly{[9,9-dimethyl-2,7-fluorenylene]-alt-[1,2-bis(p-phenylene)-1-cyanovinylene]} (PFCN), were studied employing density functional theory (DFT) and time dependent density functional theory (TD-DFT) with B3LYP functional. The electronic properties of the neutral molecules, extrapolated ionization potentials (IP) and electron affinities (EA), and energy gaps were investigated in comparison with pristine poly(2,7- fluorenylene). From comparison with poly(2,7-fluorenylene) (PF), the 1,2-bis(p-phenylene)-1-cyanovi- nylene unit was found to be a good electron-withdrawing moiety for electronic materials and the incorporation of 1,2-bis(p- phenylene)-1-cyanovinylene resulted in a narrow band gap and a red shift of both the absorption and photoluminescence emission peaks. Most importantly, the LUMO energies of PFCN are around 1 eV lower than those of PF, which results in the decrement of EA about 0.9 eV, indicating that the 1,2-bis(p-phenylene)-1-cyanovinylene unit has significantly improved the electron-accepting properties of the copolymer PFCN. Substitution of 2,5-dimeth- oxy-p-phenylene for 9,9-dimethyl-2,7-fluorenylene induced larger band gaps and thus a blue-shift in absorption and emission peaks, which can be attributed to the better conjugated backbone in PFCN.
Details
- ISSN :
- 16147065 and 1001604X
- Volume :
- 25
- Database :
- OpenAIRE
- Journal :
- Chinese Journal of Chemistry
- Accession number :
- edsair.doi...........42d7dfd0f9228eab0863c7057617896f