CONFORMATIONS OF 2,2'-BIPYRROLE pi-SYSTEMS HAVING AN ELECTRON-DONATING SITE AT ONE TERMINAL AND ELECTRON-ACCEPTING SITE AT THE OTHER TERMINAL IN THE GROUND AND EXCITED STATES

摘要

Various symmetrical and unsymmetrical l,l',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 (approx 160 nm),suggesting effective conjugation through the pi-system,which consists of the central 2,2'-bipyrrole,5-aryl group,and 5'-aryl group,in the excited state.