INVESTIGATION OF EXCITED-STATE CHARGE-TRANSFER WITH STRUCTURAL-CHANGEIN COMPOUNDS CONTAINING ANILINO SUBUNITS BY SUBPICOSECOND SPECTROSCOPY

Subpicosecond absorption spectroscopy and picosecond streak camera flu orometry are applied to the study of the photoinduced processes in thr ee classes of compounds for which molecular torsion with charge locali zation leading to an emissive or non-emissive twisted internal charge transfer state was proposed. The compounds are classified according to their steady-state fluorescence properties: compounds having a single band without solvatochromism or a single band with solvatochromism an d compounds exhibiting dual fluorescence in polar solvents. The select ed compounds are di- and tri-phenylmethane and amino-rhodamine dyes fo r the first class, the laser dye DCM for the second class and a substi tuted triphenylphosphine for the third class. These compounds contain at least one electron-donating anilino-group able to rotate. In all ca ses, the transient spectroscopy gives evidence for an excited-state re laxation involving the formation of an intermediate state. The changes observed in the kinetics by changing the solvent viscosity and polari ty and upon donor protonation bring support to a mechanism involving p hotoinduced charge transfer with structural change. The kinetics are t entatively discussed within the context of theories of electron transf er reactions in the condensed phase. (C) 1997 Elsevier Science S.A.