Photophysical properties of free-base and manganese(iii) N-confused porphyrins

Abstract

The photophysical properties of N-confused 5,10,15,20-tetraphenyl porphyrin derivatives have been studied using steady-state and time-resolved spectroscopic techniques. The peripherally substituted N-confused 5,10,15,20-tetraphenyl free-base porphyrins (NCTPPs) show stronger B-band absorptions in DCM than in DMAc, while much stronger emissions have been observed in DMAc, which may be due to the shorter times (τ_IC) of internal conversion from the B-band to the Q-band. The Q-band spectral structures of NCTPPs in DCM are significantly different from those in DMAc. The introduction of ortho-OCH₃ results in the strongest emission in both DCM and DMAc and significant fluorescence after N-methylation even though the emissions of other N-methyl complexes are quenched. The N-methylation of NCTPPs leads to a larger τ_IC and shorter emission lifetime. The excited-state dynamics of manganese(III) N-confused porphyrins (Mn(Cl)NCH₃NCTPPs) are influenced by both peripheral substituents and manganese(III) metal ion, and exhibit ultrafast intersystem crossing processes.