New Cu() halide complexes showing TADF combined with room temperature phosphorescence: the balance tuned by halogens

A series of Cu( i ) halide complexes derived from tris(2-pyridyl)phosphine (Py 3 P), [Cu 2 (Py 3 P) 2 X 2 ] (X = Cl, Br, I), have been synthesized by a straightforward reaction in solution or through a mechanochemical route. At room temperature, the solid complexes exhibit bright dual-mode photoluminescence ( λ max = 520-550 nm, τ = 14.5-20.0 μs, and Φ PL 53%), expressed by thermally activated delayed fluorescence (TADF) combined with phosphorescence (PH), originating from 1 (M + X)LCT and 3 (M + X)LCT excited states, respectively. Remarkably, the balance of these radiative processes at 300 K is regulated by halogen atom nature, switching from TADF-assisted phosphorescence to PH-admixed TADF. The emission of [Cu 2 (Py 3 P) 2 Cl 2 ] at 300 K is largely contributed by PH (73%) admixed with the TADF fraction (27%) and [Cu 2 (Py 3 P) 2 Br 2 ] also emits mainly PH (65%) admixed with the larger TADF fraction (35%). Meanwhile, for [Cu 2 (Py 3 P) 2 I 2 ], the TADF channel becomes dominating (61%) and PH contribution drops to 39%. The photophysical study corroborated by (TD)DFT computations has revealed that this effect arises mainly from the narrowing of the Δ E (S 1 − T 1 ) gap of the [Cu 2 (Py 3 P) 2 X 2 ] complexes in the order Cl (1500 cm −1 ) > Br (1250 cm −1 ) > I (1000 cm −1 ) which facilitates the TADF pathway and suppresses PH in the same order. A series of Cu( i ) halide complexes showing thermally activated delayed fluorescence (TADF) combined with room temperature phosphorescence are reported.