Kinetic model for the molecular system of Zinc(II)-2,9,16,23-phthalocyanine tetracarboxylate

Abstract

Using vis absorption, fluorescence spectral experimental data, and time-resolved measurement, we have examined the kinetics of Zinc(II)-2,9,16,23-phthalocyanine tetracarboxylate ( ZnPc ( COONa )4), which is interesting photosensitizer of far red-absorption in water: NaOH solution. The kinetic parameters were measured and/or calculated. The photophysical properties originate principally from the planar macrocycle while the outer substituent and degree of carboxylation seem not to have a considerable influence on the kinetic parameters. The nonradiative rate constants of the first excited state were dominant due to the heavy metal effect. Using the obtained photophysical parameters, the population dynamics were calculated by kinetic model. On nanosecond scale of 15 ns, about 63% population of the first excited-singlet state is retrieved by the ground state. Whereas, the rest of population are deactivated to the first excited-triplet state. Later on, during about 7 μs starting from the initial decay of the first excited singlet state, the first excited singlet state and the first excited triplet state were completely empty, meanwhile the ground state retrieved its initial population. Due to the fact that ZnPc ( COONa )4 has strong absorption, long lifetimes of the first singlet and triplet excited states, and fast intersystem crossing, it may be suitable for nonlinear optical studies.