Millisecond-Long Red Phosphorescence in Chiral Heteroleptic Ag(I) Complexes Bearing Benzothiazole Ligands

Six orange-red phosphorescent chiral Ag(I) complexes of general structure [Ag(N1^N2)(P^P)]PF6, where N1^N2 is a pyridyl- or quinolyl-functionalized benzo[d]thiazole and P^P is an enantiopure diphosphine of the BINAP family with axial chirality, are herein presented. The novel complexes have been extensively characterized from a chemical, structural, and photophysical point of view, resulting in a family of chiral Ag(I) coordination compounds with red photoluminescence. Their emissive properties can be attributed to ligand-centered triplet manifold excited states localized on the benzothiazole ligand (3LCbtz). Low photoluminescence quantum yield (PLQY) values are recorded in solution, as is typical of Ag(I) derivatives, whereas a remarkable switch-on of the emission is observed in the solid state, with samples of quinolyl-benzothiazole xylBINAP complexes R-3 and S-3 displaying PLQY as high as 50% and excited-state lifetimes in the millisecond range. Electron circular dichroism (ECD) spectra show strong activity in both solution and solid state as thin films for all the complexes. Time-dependent density functional theory (TD-DFT) calculations confirm the strong LCbtz nature of the major absorbing singlet and emissive triplet states and provide an argument behind the absence of circularly polarized luminescence (CPL) in these samples.