Shell effects on hole-coupled electron transfer dynamics from CdSe/CdS quantum dots to methyl viologen

摘要

Electron transfer (ET) dynamics from the 1S(e) electron state in quasi-type II CdSe/CdS core/shell quantum dots (QDs) to adsorbed methyl viologen (MV2+) were measured using femtosecond transient absorption spectroscopy. The intrinsic ET rate k(ET) was determined from the measured average number of ET-active MV2+ per QD, which permits reliable comparisons of variant shell thickness and different hole states. The 1S(e) electron was extracted efficiently from the CdSe core, even for CdS shells up to 20 angstrom thick. The ET rate decayed exponentially from 10(10) to 10(9) s(-1) for increasing CdS shell thicknesses with an attenuation factor beta approximate to 0.13 angstrom(-1). We observed that compared to the ground state exciton 1S(e)1S(3/2) the electron coupled to the 2S(3/2) hot hole state exhibited slower ET rates for thin CdS shells. We attribute this behaviour to an Auger-assisted ET process (AAET), which depends on electron-hole coupling controlled by the CdS shell thickness.