Photophysical properties of electron-deficient free-base corroles bearing meso-fluorophenyl substituents.

The ultrafast photophysical behaviors of a series of meso-fluorophenyl substituted electron-deficient free base corroles F0C, F5C, F10C and F15C in toluene have been investigated using femtosecond time resolved absorption spectroscopy and steady-state spectroscopy. The S2→S1* transformation was found to be accelerated with the enhancement of electron-deficiency (from 550 fs for F0C to 140 fs for F15C), while S1*→S1 prolonged from ∼9 ps for F0C to ∼24 ps for F15C, which was assigned to an intermolecular vibrational cooling process. The intersystem crossing process was directly observed. The intersystem crossing rate constant (kISC) from S1 to T1 was found to increase significantly with the fluorophenyl substituents (from F0C to F10C), while it does not totally follow the trend of the increase of the atomic number of the peripheral fluorine atoms. The order of ISC time constants from larger to smaller is F0C < F5C < F10C > F15C. It indicates that the electron-withdrawing effect of fluorophenyl substitutions, together with the heavy atom effect, influences the photophysical properties of excited states of corroles.