Photophysics of some indolizines, derivatives from bipyridyl, in various media

A series of photoluminescent properties of some new indolizinic compounds, recently synthesized, derivatives from bipyridyl, are analyzed. Significant differences are observed between monoindolizinic compounds and bisindolizi nic ones regarding the absorption and fluorescence in the UV-VIS spectral r ange. Extended conjugation in bisindolizinic compounds causes a strong incr ease in the molar absorptivity and fluorescence quantum yield and a shift o f the fluorescence spectrum towards violet. Unlike monoindolizinic compound s, the bisindolizinic ones realize both an almost planar conformation and a rigidization of the molecule, in the sense that it changes less its dimens ion after excitation. It is estimated that the transitions of the analyzed molecules are of the type pi --> pi* and that the mixing of the S-1 and S-2 states is achieved to a small extent. (C) 1999 Published by Elsevier Scien ce B.V. All rights reserved.