Luminescence Properties of Protonated ortho-Substituted meso-Tetraarylporphyrins

摘要

Luminescence properties of meso-tetrakis-(2, 6-diflourophenyl)porhyrin (o-TDFPP) dication formed in acidified organic solvents are investigated and compared with those obtained earlier for meso-tetraphenylporphyrin (TPP) and meso-tetrakis-(o-tolyl)porphyrin (o-TTP). The ortho-Substitution in phenyl groups of protonated porphyrins results in a hypsochromic shift of the absorption bands, which is explained by weakening of conjugation of phenyl groups with a macrocycle due to steric hindrances. In the case of o-TDFPP, the hypsochromic shift and a decrease in the intensity of the Q(0-0) band are enhanced, suggesting the significant inductive effect of electronegative fluorine atoms. The fluorescence of o-TDFPP is quenched as compared to that of o-TTP not only for protonated molecules, but also for free bases. The additional pathway for nonradiative relaxation is related to the transitions to intramolecular charge-transfer states. At 77 K, fluorescence of the free-base o-TDFPP, is not quenched, whereas that of the protonated molecule is quenched. The phosphorescence of protonated o-TDFPP is, on the contrary, more intense than that of TPP and o-TTP.