Fluorescence properties of the dicationic porphyrin 5,15-DiMPyP orderly aggregated along DNA surface.

5,15-bis(4-N-methylpyridyl)-10,20-diphenylporphyrin (5,15-DiMPyP, also known as t-H2Pagg) is capable of forming long-range ordered DNA-templated aggregates in solution. The present work reports the study of fluorescent properties of 5,15-DiMPyP, both monomeric and aggregated in presence of DNA, performed by means of steady-state and time-resolved fluorescence spectroscopy. The S1 state of free monomeric 5,15-DiMPyP is affected by a low-lying intramolecular charge transfer state which is destabilized upon porphyrin monomer binding to DNA. The aggregates, DNA-templated and random, of 5,15-DiMPyP were found to be emissive in solution and had respective S1 state lifetimes of 1.8 ns and 5.2 ns.