Ultrafast dynamics of alkyl-substituted porphycenes in solution

Dynamics of relaxation from higher electronic excited states was studied for 9, 10, 19, 20-tetraalkylporphycenes with methyl and propyl substitutents. Depopulation of S3/S4 Soret states leading into S2/S1 Q levels occurs in about 50 fs. This time is similar, or even shorter than that recently determined for porphyrin, even though the Q-Soret energy separation in the latter is about twice smaller than in porphycenes. The time constant for H or D transfers are shorter than 50 fs indicating very low energy barriers to their transfer. The non-radiative rate constants of both derivatives are related to the motion of the alkyl chain.