Femtosecond studies of the excited-state dynamics of ester-alkyloxy substituted zinc phthalocyanines

The ultrafast dynamics of two zinc(II) phthalocyanine derivatives with potential applications in photodynamic therapy was studied by femtosecond transient absorption spectroscopy. The kinetic features of the compounds were determined at excitation wavelengths within the Soret and the Q-bands. Three time constants revealed in time-resolved data were identified with the processes of solvent relaxation, heat transfer from the molecule to the solvent and the excited-state deactivation. The presence of long ester-alkyloxy substituents at non-peripheral positions of the molecule leads to the slow-down of the thermalization of the molecules and shortens the excited-state lifetime by a factor of approximately 3.