Influence of Coordinated Anions on Charge Transfer and Thermally Activated Delayed Fluorescence in Copper(I) Complexes

This work investigates the influence of coordinated anions on the structural, electronic, and photophysical properties of two neutral copper(I) complexes, [Cu(X)(Phen)(PPh₃)] (X = NCS⁻ or I⁻), with particular emphasis on their thermally activated delayed fluorescence (TADF) behavior. Resonance Raman spectroscopy combined with TDDFT calculations was employed to elucidate the charge-transfer character of the NCS^-containing complex, while steady-state and time-resolved photoluminescence measurements were performed to probe the excited-state dynamics of the iodide analogue. The iodide complex exhibits intense red emission under UV and X-ray excitation and displays clear thermally activated delayed fluorescence with prompt (17.1 ns) and delayed (1.1 μs) fluorescence components, whereas the isothiocyanate analogue is only weakly emissive. These findings demonstrate the significant role of coordinated anions in modulating charge-transfer states and excited-state dynamics, providing valuable insights for the design of efficient copper(I)-based TADF emitters for OLED applications.