Synthesis and electronic properties of new small band gap conjugated polymers, methine-bridged poly(3,4-ethylenedioxy pyrrole) (PEDOP) are reported. Density functional theory (B3LYP with 6-31G basis) are used to obtain the optimizei ground-state geometries and electronic structures of PEDOP and poly [(3,4-ethylenedioxypyrrole-2,5-diyl) methine (PEDOP-M). Theoretical bond length alternation of PEDOP is reduced by incorporating the methine bridge and leads to th band gap reduction from 2.44 to 0.68 eV. The small band gap characteristic of PEDOP-M is further verified by preparing twi conjugated polymers, poly [(2,5-n-benzyl-3,4-ethylenedioxypyrrolediyl)-benzylidene-(2,5-n-benzyl-3, 4-ethylenedioxypyr role-quinodimethanediyl)] (PbEDOP-b) and poly [(2,5-n-benzyl-3,4-ethylenedioxypyrrolediyl)-(p-nitrobenzylidene)-(2, 5-n-benzyl-3,4-ethylenedioxypyrrole-quinodimethanediyl)] (PbEDOP-nb). The optical band gap of PbEDOP-b and PbEDOP nb are 1.77 and 1.45 eV, respectively, while the electrochemical band gap of the former is 1.59 eV. Although the bulky side groups of these two polymers result in a larger band gap than that of PEDOT-M, it indicates the small band gaps of such polymers. The nitrobenzene group could extend the π-conjugation and lead to the smaller band gap of PbEDOP-nb than that of PbEDOP-b. The present study suggests that methine-bridged poly(3,4-ethylenedioxypyrrole) is a class of small band gap polymers.
All Science Journal Classification (ASJC) codes
- Polymers and Plastics
- Materials Chemistry