Enhancement of the Yield of Photoinduced Charge Separation in Zinc Porphyrin-Quantum Dot Complexes by a Bis(dithiocarbamate) Linkage

This paper describes the use of a phenyl bis(dithiocarbamate) (PBTC) linker to enhance the quantum yield of photoinduced electron transfer (eT) from a zinc porphyrin (ZnP) molecule (donor) to a CdSe quantum dot (QD) (acceptor), where quantum yield is defined as the fraction of photoexcited ZnP molecules in the sample that donate an electron to the QD. The PBTC ligand links the ZnP to the QD by coordinating to Cd2+ on the surface of the QD and the Zn metal center in ZnP via its dithiocarbamate groups. Compared with the donor-acceptor complex formed in the absence of PBTC linkers, where the ZnP molecule adsorbs to the QD through its carboxylate moiety, the PBTC linkage increases the binding affinity between ZnP molecules and QDs by an order of magnitude, from 1.0 x 10(5) +/- (0.7 x 10(4)) M-1 to 1.0 x 10(6) +/- (1.0 x 10(5)) M-1, and thereby increases the eT quantum yield by, for example, a factor of 4 (from 8% to 38%) within mixtures where the molar ratio ZnP:QD = 1:1.