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.