Accurate Investigation on the Fluorescence Resonance Energy Transfer between Single Organic Molecules and Monolayer WSe by Quantum Coherent Modulation-Enhanced Single-Molecule Imaging Microscopy.

Hybrid organic two-dimensional (2D) materials heterostructures are attracting tremendous attention for optoelectronic applications due to their low-cost processing and complementary advantages. However, accurate understanding of the fundamental physics on the interface of the hybrid heterostructures at the single-molecule level remains largely unexplored. Here, we investigated the fluorescence resonance energy transfer (FRET) between the single organic molecules and monolayer WSe through a newly developed single molecule microscopy technique, quantum coherent modulation-enhanced single-molecule imaging microscopy (QCME-SMIM). It is shown that the extremely weak energy transfer signal was successfully extracted from the huge fluorescence background, originating from the emission of monolayer WSe. The observed energy transfer efficiency is in agreement with a d distance dependence, with a Förster radius of ∼6 nm for the hybrid structures. Our work not only provides valuable insight into the FRET process at the single-molecule level across such hybrid organic-2D interfaces, but also demonstrates the feasibility of the newly developed technique for investigating the fundamental physics of electron transfer kinetics.