Functionalized Violet-Emitting Cd, Pb-Free Quantum Dots with Thermally Activated Delayed Photoluminescence for Efficient Photochemical Reactions

Colloidal quantum dots (QDs) are excellent luminescent materials, but their short exciton lifetime, typically in the nanosecond range, restricts their applications in photochemical reactions. By designing QD-molecule conjugates, the exciton energy can be cycled between the QD exciton state and the molecular triplet state through triplet energy transfer, thereby prolonging the exciton lifetime to hundreds of microseconds, which is similar to the mechanism of thermally activated delayed fluorescence in molecules. Currently, QD-molecule-based thermally activated delayed photoluminescence (TADPL) systems have covered the blue to near-infrared spectral range. Here, we extend the reach of TADPL to the violet band, including slight penetration into the ultraviolet, by using Cd, Pb-free ZnSe/ZnS core/shell QDs functionalized with biphenyl ligands, which exhibit the highest TADPL energy (up to 3.0 eV) reported to date for QD-molecule conjugates. The high exciton energy, long lifetime (80 μs), and high TADPL quantum yield (23.7%) of the ZnSe/ZnS-biphenyl system enable very high efficiency in a variety of QD-sensitized photochemical reactions.