Dinuclear Cu(I) Complex with Combined Bright TADF and Phosphorescence. Zero-Field Splitting and Spin–Lattice Relaxation Effects of the Triplet State

Abstract

The three-fold bridged dinuclear Cu(I) complex Cu(μ-I)(1 N- n-butyl-5-diphenyl-phosphino-1,2,4-triazole), CuI(P^N), shows bright thermally activated delayed fluorescence (TADF) as well as phosphorescence at ambient temperature with a total quantum yield of 85% at an emission decay time of 7 μs. The singlet (S)-triplet (T) energy gap is as small as only 430 cm (53 meV). Spin-orbit coupling induces a short-lived phosphorescence with a decay time of 52 μs ( T = 77 K) and a distinct zero-field splitting (ZFS) of T into substates by ∼2.5 cm (0.3 meV). Below T ≈ 10 K, effects of spin-lattice relaxation (SLR) are observed and agree with the size of ZFS. According to the combined phosphorescence and TADF, the overall emission decay time is reduced by ∼13% as compared to the TADF-only process. The compound may potentially be applied in solution-processed OLEDs, exploiting both the singlet and triplet harvesting mechanisms.

Syntheses, Crystal Structures and Photophysical Properties of Dinuclear Copper(I) Complexes Bearing Diphenylphosphino‐Substituted Benzimidazole Ligands

“…Careful examination of the emission decay times at various temperatures reveal that the excited‐state lifetimes do not reach a plateau at low temperature. Similar phenomena have already been reported, which have been demonstrated to ascribe the zero‐field split of the T 1 state [26,28] . Accordingly, the significant zero‐field splitting of T 1 further confirms the high SOC efficiency in the complex [29]…”

“…The exchange energy, ΔE ST , is only 161 cm −1 (0.020 eV). To the best of our knowledge, the energy separation (ΔE ST ) is among the smallest reported for Cu‐based TADF emitters, [7a,26] which can greatly accelerate an efficient up‐conversion and result in a dominating TADF. The above preliminary results indicate that thermal equilibration between electronically excited states (S 1 and T 1 ) is achievable even at low temperature, which results in an unusually gradual intensity decrement for TADF by increasing of the temperature.…”

Recent Advancements in and the Future of Organic Emitters: TADF‐ and RTP‐Active Multifunctional Organic Materials

“…Recently, there was a report of organometallic compounds that exhibited both TADF and RTP processes. The Yersin group synthesized copper complex Cu 2 I 2 (P^N) 3 (Figure ), but the problem of using organometallic complexes remained.…”

Modulation of emission properties of phosphine-sulfonate ligand containing copper complexes: playing with solvato-, thermo-, and mechanochromism

“…Nevertheless, similar absence of red shift were reported independently by Osawa and by Yersin, which do not exclude TADF processes. [17,29] Emission decay profile for Cu-1 suggests that the pure triplet state τ(T 1 ) is reached below 78K. Small values were obtained by fitting the sigmoid decay curves…”

“…This could prevent vibrational quenching or deactivation through structural distortion from the tetrahedral to quasi-square-planar coordination geometry ( Figure 4). [17,19,29]…”