One- and two-photon electron-transfer induced uncaging of coumarin from cinnamate-capped CdSe quantum dots

摘要

It has been previously shown that visible-light excitation of CdSe quantum dots (QD) functionalized with a cinnamate ligand (4-Diethylamino-2-hydroxythiocinnamate; 4DEATC) can induce uncaging of a fluorescent coumarin molecule (7-Diethylaminocoumarin; 7DEAC). In the current study, the quantum yield, QY, for this photochemical uncaging process is determined. In addition, the results of visible-light excitation of cinnamate-capped CdSe and cinnamate-capped CdSe/ZnS QDs are compared. The uncaging of coumarin is observed only for the functionalized core CdSe QDs, and not for CdSe/ZnS core-shell QDs. These results strongly support that the uncaging of coumarin from cinnamate-capped QDs occurs via an electron-transfer step from the QD to the cinnamate ligand, and the large band gap of the ZnS shell blocks electron transfer from CdSe core to the ligand. In addition, it is demonstrated that coumarin uncaging from cinnamate-capped CdSe can be induced using pulsed NIR (1064 nm) excitation of the QD via a two-photon process. The two-photon absorbance cross section and twophoton absorbance action cross section are estimated by combining the results of the one- and two-photon uncaging experiments.