Surface effects on quantum dot-based energy transfer.

CdSe quantum dot (QD)-phthalocyanine (Pc) conjugates were prepared as energy transfer donor-acceptor pairs, and the efficiency of the energy transfer process in this system was investigated as a function of QD size and under different surface chemistry conditions. The kinetics and efficiency of the energy transfer process were studied by femtosecond time-resolved laser spectroscopy. We observed that the energy transfer efficiency does not follow a linear dependence on spectral overlap integrals as predicted by the Förster theory for molecules. This observation is found to be due to the involvement of QD surface states in the energy transfer process from the photoexcited QDs to the molecular energy acceptor.