Reducing lifetime in Cu(i) complexes with thermally activated delayed fluorescence and phosphorescence promoted by chalcogenolate–diimine ligands

Abstract

Luminescent copper(I) complexes have drawn attention due to their promising performance as alternative optoelectronic materials to the well-known heavy transition metal complexes. Herein, we report the synthesis of six luminescent Cu(I) complexes with phosphines and 1,10-phenanthroline-derived ligands with thiadiazole and selenodiazole groups in order to evaluate the effect of the heavy atom on their photophysical properties. Steady-state and time-resolved spectroscopy confirmed delayed fluorescence emission via a thermally activated delayed fluorescence mechanism in all cases. The experimental spectroscopic data were analyzed with detailed quantum-chemical calculations. Interestingly, these complexes did not show the expected “heavy atom effect” that enhances the spin–orbit coupling matrix elements, but nevertheless the addition of the heavier chalcogens contributed to reducing the photoluminescence lifetime to roughly 800 ns, which is the lowest reported so far for such TADF materials.