Primary ultrafast events preceding the photoinduced proton transfer from pyranine to water

Femtosecond fluorescence and absorption spectroscopies are used to probe th e early events of the photoinduced proton transfer (PT) from pyranine to wa ter. The process is found to involve two ultrafast steps (300 fs and 2.5 ps ) which precede the relatively slow (87 ps) PT step. From the comparative s tudy of the properties of the excited acid and its conjugate anion in vario us aqueous and alcoholic media, these ultrafast steps are identified as the solvation dynamics of the locally excited (LE) state of the acid and its s ubsequent relaxation to an intermediate electronic state, whose nature is d iscussed. (C) 2000 Elsevier Science B.V, All rights reserved.