Thermally Activated Delayed Fluorescence (TADF) in Coinage Metal Nanoclusters: Bridging Molecular and Nanoscopic Photophysics

Thermally activated delayed fluorescence (TADF) in coinage metal nanoclusters (CMNCs) has introduced new paradigms in the design of optoelectronic materials, uniting atomic precision with tunable quantum and photophysical properties. This review provides a critical and comprehensive analysis of TADF mechanisms in gold, silver, copper, and doped/alloy nanoclusters, emphasizing quantum confinement, strong spin-orbit coupling, and engineered singlet-triplet energy gaps that enable efficient reverse intersystem crossing and high photoluminescence quantum yields. Recent advances in TADF-active CMNCs are highlighted, including ligand architecture, core composition, supramolecular assembly, and heterometallic doping, which collectively afford unprecedented control over emission color, dynamics, and stability. Comparative perspectives versus organic and metal-organic TADF emitters are presented, underscoring the distinctive advantages and ongoing challenges of CMNCs. Current and emerging applications in OLEDs, X-ray scintillation, chiral photonics, and bioimaging are discussed, along with future research directions and critical barriers to the realization of CMNCs in next-generation optoelectronic devices.