Electronic and vibrational coherences in resonance energy transfer along MEH-PPV chains at room temperature'

In this work we report a study of the role of coherence dynamics in the intermediate coupling regime of electronic energy transfer (EET). Starting from the idea that in the intermediate coupling regime the phase information should be partially retained in a transfer process from a donor to an acceptor, we designed a new ultrafast experiment based on anisotropy decay along two time axes, capable of probing the degree of coherence characterizing this transfer. Conjugated polymer (poly[2-methoxy-5-(2'-ethyl-hexoxy)-1,4-phenylenevinylene], MEH-PPV) samples with different chain conformations were examined as a model multichromophoric system. The data, recorded at room temperature, reveal coherent transfer associated with intrachain energy transfer. These results were extended using two-dimensional photon echo measurements, which revealed the presence of long-lived intrachain electronic and vibrational coherences. Our results suggest that, in the intermediate coupling regime, quantum transport effects can occur when chemical bonds connecting donor and acceptor help to correlate their energy gap fluctuations. Moreover, they influence the mechanism of EET, even at room temperature.