Electronic transition moment directions in indoloindoles: the use of orientation amplifiers

Indolo[3,2-b]indole and its four derivatives are studied by linear dichrois m in stretched polymeric sheets, fluorescence anisotropy in glassy solution s, and by quantum chemical calculations. Poor alignment of the parent molec ule in the stretched polymers does nor allow the determination of the trans ition moment directions by standard procedures. However, this is made possi ble if long inert substituents are introduced into the molecule. Their role is to increase the alignment without modifying the electronic structure of the chromophore. For a well-oriented chromophore, principal orientation fa ctors and polarizations of transitions may be obtained. The results show th at for the four lowest observed excited singlet states of indolo[3,2-b]indo le, all the pi pi* character, substitution by carboethoxy or alkyl groups d oes not alter the directions of the transition moments. (C) 1999 Elsevier S cience B.V. All rights reserved.