Energy transfer-enhanced photocatalytic reduction of protons within quantum dot light-harvesting–catalyst assemblies

Abstract

Excitonic energy transfer (EnT) is the mechanism by which natural photosynthetic systems funnel energy from hundreds of antenna pigments to a single reaction center, which allows multielectron redox reactions to proceed with high efficiencies in low-flux natural light. This paper describes the use of electrostatically assembled CdSe quantum dot (QD) aggregates as artificial light harvesting-reaction center units for the photocatalytic reduction of H+ to H2, where excitons are funneled through EnT from sensitizer QDs (sQDs) to catalyst QDs (cQDs). Upon increasing the sensitizer-to-catalyst ratio in the aggregates from 1:2 to 20:1, the number of excitons delivered to each cQD (via EnT) per excitation of the system increases by a factor of nine. At the optimized sensitizer-to-catalyst ratio of 4:1, the internal quantum efficiency (IQE) of the reaction system is 4.0 ± 0.3%, a factor of 13 greater than the IQE of a sample that is identical except that EnT is suppressed due to the relative core sizes of the sQDs and cQDs. A kinetic model supports the proposed exciton funneling mechanism for enhancement of the catalytic activity.