Ultrafast decay dynamics of photoexcited Cu(II)(TMpy-P4) in water solvent

Femtosecond time-resolved absorption spectroscopy was employed to investigate the relaxation dynamics of photoexcited copper(II) tetrakis (4-N-methylpyridyl)porphyrin (Cu(II)(TMpy-P4)) in neat water. The transient absorption spectra and their temporal profiles show a strong pump-power dependence reflecting multiphoton ionization of water, which probably caused the discrepancies in the previous reports. Time-resolved transient absorption spectra were recorded under low pump-power condition to avoid the multiphoton effect. It was confirmed that the relaxation process finishes within 100 ps, exhibiting the double exponential recovery of Cu(II)(TMpy-P4) ground state. The relevant mechanism for the relaxation dynamics of photoexcited Cu(II)(TMpy-P4) in water was proposed.