Femtosecond transient absorption spectroscopy of non-substituted photochromic spirocompounds

Primary processes in spironaphtopyran (SNP), spironaphtoaxazine (SNO) and s pirophenantrooxazine (SPO) after excitation by the femtosecond light pulse with the carrier wavelength 308 nm were studied by the absorption 'pump-pro be' method with femtosecond time resolution. Probing was performed by means of the super-continuum light pulse with the carrier wavelength in the rang e 420-580 nm. Registration of the photoinduced absorption spectra dynamics allowed to observe time evolution of all intermediates. It appeared that ph otoinduced transformation of all three compounds has the same mechanism. Ki netic scheme is suggested and all rate constants entering this scheme are d etermined. (C) 2000 Elsevier Science B.V. All rights reserved.