Activation of TADF in Photon Upconverting Crystals of Dinuclear Cu(I)-Iodide Complexes by Ligand Engineering

This work reports that ligand engineering can modulate the triplet harvesting mechanism in iodide-bridged rhombic Cu₂I₂ complexes. Complex-1, with a smaller Cu-Cu distance, exhibits phosphorescence from ³(M+X)LCT and ³CC states with 66% quantum yield, whereas an increased Cu-Cu distance in complex-2 results in a switch of the emission from phosphorescence to TADF, which occurs via ^1/3(M+X)LCT states with 83% quantum yield. The TADF property of complex-2 has been utilized for the fabrication of a pc-LED emitting efficient warm white light. Moreover, the high charge-transfer nature of these complexes leads to the emergence of third-harmonic generation (THG). Interestingly, complex-1 exhibits efficient third-harmonic generation with a χ⁽³⁾ value of 1.15 × 10^-18 m² V^-2 and LIDT value of 14.73 GW/cm². This work aims to provide a structure-property relationship to achieve effective harvestation of triplet excitons in iodide-bridged rhombic Cu₂I₂ complexes and their effective utilization in OLED device fabrication and nonlinear photon upconversion processes.