A Class of Promising Merocyanine-Functionalized Cd₃₃Se₃₃ Quantum Dots with Strong Fluorescence Emission in Tetrahydrofuran and Acetonitrile

Owing to the existence of surface defects, quantum dots (QDs) could be unstable, and thus, the design of proper ligands to improve their stability and optical performance is challenging. In this work, four D-π-<i>A</i> ligands were designed by modulating the D part of merocyanine and were grafted onto Cd₃₃Se₃₃ QD via a Cd-S bond, forming Cd₃₃Se₃₃@D-π-<i>A</i> complexes. It was found that a hole trap appeared between the HOMO and LUMO of the Cd₃₃Se₃₃@D-π-<i>A</i> complexes in vacuum, and the stronger the electron-donating capability of the D part, the higher the activation energy of the trap, which disappeared in solvent environments. The ligand-to-metal charge transfer (LMCT) mechanism of Cd₃₃Se₃₃@D-π-<i>A</i> complexes induced a fluorescence quenching phenomenon in vacuum, while in solution, the local excitation on the D-π-<i>A</i> ligand facilitated stronger fluorescence due to the enhanced electron-donating capability of its D part. The present study provides a strategy for improving the optical performance of functional QDs through the design and optimization of D-π-<i>A</i> ligands, shedding light on the development and applications of novel functional QDs.