Electron-transfer dynamics in DTDCI/MoS2 and DTDCI/WS2 nanoclusters

The kinetics of forward and reverse electron transfer (ET) between an organic cyanine dye and semiconductor nanoclusters have been studied. The systems studied are MoS2/DTDCI and WS2/DTDCI (DTDCI = diethylthiodicarbocyanine iodide). The static spectroscopy of these systems indicates that the dye adsorbs on the nanoclusters as monomers. The vast majority of excited-state dye molecules are quenched by rapid (<10 ps) electron injection in the nanocluster. The reverse ET kinetics are elucidated by time-resolved absorption (bleach recovery) measurements. The results indicate that there are two components of reverse ET that take place on the tens to hundreds of picoseconds and >10 ns time scales. These components are assigned to reverse ET from shallow (tens to hundreds of picoseconds) and deep (>10 ns) trap states. The shorter time scale component is nonexponential and is fit with distributed kinetics model, in which the Bohr radius of the trapped electron is about 2.2 nm. This value of the Bohr radius is comparable to that obtained from electron/hole recombination studies.