A bichromophoric model system-a short peptide labeled with tetramethylrhodamine (TMR) and the carbocyanine Cy5-embedded 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 (T-1 --> T-N --> S-1 --> S-0) in single Cy5 molecules. We observed that even with 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.