Pyridylarsine-based Cu(i) complexes showing TADF mixed with fast phosphorescence: a speeding-up emission rate using arsine ligands

Can arsine ligands be preferred over similar phosphines to design Cu(i)-based TADF materials? The present study reveals that arsines can indeed be superior to reach shorter decay times of Cu(i) emitters. This has been exemplified on a series of bis(2-pyridyl)phenylarsine-based complexes [Cu-2(Py2AsPh)(2)X-2] (X = Cl, Br, and I), the emission decay times of which are significantly shorter (2-9 mu s at 300 K) than those of their phosphine analogs [Cu-2(Py2PPh)(2)X-2] (5-33 mu s). This effect is caused by two factors: (i) large Delta E(S-1-T-1) gaps of the arsine complexes (1100-1345 cm(-1)), thereby phosphorescence is admixed with TADF at 300 K, thus reducing the total emission decay time compared to the TADF-only process by 5-28%; (ii) higher SOC strength of arsenic (zeta(l) = 1202 cm(-1)) against phosphorus (zeta(l) = 230 cm(-1)) makes the k(r)(T-1 -> S-0) rate of the Cu(i)-arsine complexes by 1.3 to 4.2 times faster than that of their phosphine analogs. It is also noteworthy that the TADF/phosphorescence ratio for [Cu-2(Py2AsPh)(2)X-2] at 300 K is halogen-regulated and varies in the order: Cl (1 : 1) < Br (3 : 1) approximate to I (3.5 : 1). These findings provide a new insight into the future design of dual-mode (TADF + phosphorescence) emissive materials with reduced lifetimes.