Direct Observation of Collective Blinking and Energy Transfer in a Bichromophoric System

Abstract

A bichromophoric model systema short peptide labeled with tetramethylrhodamine (TMR) and the carbocyanine Cy5embedded in poly(vinyl alcohol) (PVA) was used to investigate energy transfer and collective blinking effects in multichromophoric systems at the level of single molecules. Experiments using direct excitation of the acceptor show evidence of photoinduced reverse intersystem crossing (T1 → TN → S1 → S0) in single Cy5 molecules. We observed that even when the Cy5 fluorophore is in the triplet state, it continues to act as an energy transfer acceptor. This demonstrates that singlet−triplet energy transfer occurs, and can lead to efficient quenching of the fluorescence of the whole bichromophoric system.