Ultrafast Energy Transfer from Bound Tetra(4-N,N,N,N-trimethylanilinium)porphyrin to Synthetic Dopa and Cysteinyldopa Melanins¶

The binding of tetra(4-N,N,N,N-trimethylanilinium)porphyrin (TAP) to melanins quenches the porphyrin emission. Time-resolved femtosecond absorption spectroscopy reveals that the mechanism behind this quenching is ultrafast nonradiative energy transfer ((tau)ET < 100 fs) from electronically excited TAP to melanin. Similar dynamics are observed for both dopa and cysteinyldopa melanins. Steady-state emission studies demonstrate that the emission from melanin increases upon excitation of bound TAP, thereby confirming that rapid energy transfer occurs. These results are consistent with previous photoacoustic studies, which revealed that the TAP-melanin complex behaves like a supermolecular system liberating heat as a whole.