Electron transfer dynamics in MoS2 nanoclusters: Normal and inverted behavior

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Abstract
The photophysics and electron transfer (ET) dynamics of quantum confined MoS2 nanoclusters have been studied using static and time resolved emission spectroscopy. The MoS2 nanoclusters consist of a single S–Mo–S trilayer, having diameters of ∼2.5 or 4.5 nm. Two types of electron acceptors are adsorbed on these nanoclusters: 2,2′-bipyridine (bpy) and 4,4′,5,5′-tetramethyl-2,2′-bipyridine (TMB). The ET reaction exothermicities may be varied by changing the electron acceptor or by varying the size of the MoS2 nanocluster. TMB is harder to reduce, and thus has a smaller ET driving force than bpy. The smaller nanoclusters have a higher energy conduction band, and thus have a larger ET driving force. In all cases, the ET driving force may be calculated from bulk MoS2 properties and quantum confinement theory. Both ‘‘normal’’ and ‘‘inverted’’ behaviors are observed. A reorganization energy of 0.40 eV is calculated from energy dependent ET rates.