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Paper | Regular issue | Vol 68, No. 2, 2006, pp.283-294
Published online, 16th December, 2005
DOI: 10.3987/COM-05-10624
Conformations of 2,2’-Bipyrrole π-Systems Having an Electron-donating Site at One Terminal and Electron-accepting Site at the Other Terminal in the Ground and Excited States

Shoji Matsumoto, Takamitsu Kobayashi, and Katsuyuki Ogura*

*Deaprtment of Applied Chemistry and Biotechnology, Faculty of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

Abstract

Various symmetrical and unsymmetrical 1,1’,5,5’-tetraaryl-2,2’-bipyrroles (1, 5, and 10) were synthesized. From their UV-VIS absorption and fluorescence spectra, the conformations of the central 2,2’-bipyrrole systems were considered as follows. These compounds adopt twisted conformations in the ground state, but their conformations in the excited state are close to planar ones. Especially, the compounds (10) bearing a formyl group and an electron-donating methoxy group showed large Stokes shifts (~160 nm), suggesting effective conjugation through the π-system, which consists of the central 2,2’-bipyrrole, 5-aryl group, and 5’-aryl group, in the excited state.