Transient absorption of photoexcited titanylphthalocyanine in various molecular arrangements

Transient absorption of photoexcited titanylphthalocyanine (TiOPc) molecule s in solids and in solution was investigated by means of the pump-probe abs orption spectroscopy with picosecond and femtosecond time resolution. The d ifferential absorption of solution was described by the absorption bleachin g, excited state absorption and stimulated emission. The latter shifts to t he long-wavelength side by approximate to9 nm with 35 +/- 10 ps time consta nt. The differential absorption spectra of TiOPc solids show dominating ble aching of the absorption band components that are strongly shifted from the absorption band of molecules in solution, while the central part of the ba nd is bleached very weakly. The contribution of the stimulated emission to the differential absorption is absent or very weak. These specific features are analyzed by discussing different models of the absorption band splitti ng. (C) 2000 Elsevier Science B.V. All rights reserved.