Oligophosphine-thiocyanate Copper(I) and Silver(I) Complexes andTheir Borane Derivatives Showing Delayed Fluorescence

摘要

The series of chelating phosphine ligands, which contain bidentate >P^>2 (bis[(2-diphenylphosphino)phenyl] ether, DPEphos; 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, Xantphos; 1,2-bis(diphenylphosphino)benzene, dppb), tridentate >P^>3 (bis(2-diphenylphosphinophenyl)phenylphosphine), and tetradentate >P^>4 (tris(2-diphenylphosphino)phenylphosphine) ligands, was used for the preparation of the corresponding dinuclear [M(μ2-SCN)>P^>2]2 (M = Cu, >1, >3, >5; M = Ag, >2, >4, >6) and mononuclear [CuNCS(>P^>3>/P^>4)] (>7, >9) and [AgSCN(>P^>3>/P^>4)] (>8, >10) complexes. The reactions of >P^>4 with silver salts in a 1:2 molar ratio produce tetranuclear clusters [Ag2(μ3-SCN)(t-SCN)(>P^>4)]2 (>11) and [Ag2(μ3-SCN)(>P^>4)]2²⁺ (>12). Complexes >7–>11 bearing terminally coordinated SCN ligands were efficiently converted into derivatives >13–>17 with the weakly coordinating ^–SCN:B(C6F5)3 isothiocyanatoborate ligand. Compounds >1 and >5–>17 exhibit thermally activated delayed fluorescence (TADF) behavior in the solid state. The excited states of thiocyanate species are dominated by the ligand to ligand SCN → π(phosphine) charge transfer transitions mixed with a variable contribution of MLCT. The boronation of SCN groups changes the nature of both the S1 and T1 states to (L + M)LCT d,p(M, P) → π(phosphine). Thelocalization of the excited states on the aromatic systems of thephosphine ligands determines a wide range of luminescence energiesachieved for the title complexes (λem varies from448 nm for >1 to 630 nm for >10c). The emissionof compounds >10 and >15, based on the >P^>4 ligand, strongly depends on thesolid-state packing (λem = 505 and 625 nm for twocrystalline forms of >15), which affects structural reorganizationsaccompanying the formation of electronically excited states.