Sky-blue thermally activated delayed fluorescence (TADF) based on Ag(i) complexes: strong solvation-induced emission enhancement

Abstract

A new Ag(I) complex based on tris(2-pyridyl)phosphine (Py₃P), [Ag₂(Py₃P)₃(SCN)₂], has been synthesized and chemically characterized. Theoretical calculations and photophysical investigations reveal thermally activated delayed fluorescence (TADF) coupled with outstanding solvato- and vapor-luminescent behavior. The parent complex [Ag₂(Py₃P)₃(SCN)₂] shows sky-blue TADF (λ_max = 469 nm) at ambient temperature with a quantum yield of Φ_PL = 16% and an emission decay time of 2.2 μs. Upon exposing the complex to CH₂Cl₂ or CHCl₃ vapors, [Ag₂(Py₃P)₃(SCN)₂]·0.66CH₂Cl₂ and [Ag₂(Py₃P)₃(SCN)₂]·CHCl₃ solvates are formed. This process is accompanied by a strong enhancement of the luminescence intensity. Both solvates also emit sky-blue TADF (λ_max = 478–483 nm), but the emission quantum yield reaches Φ_PL ≈ 70% at an emission decay time of 9–12 μs, depending on the solvent. According to DFT/TD-DFT computations, the observed TADF originates from a ¹(M + X)LCT excited state. The experimentally determined ΔE(S₁ − T₁) gap for [Ag₂(Py₃P)₃(SCN)₂]·0.66CH₂Cl₂ is relatively large and amounts to 1040 cm⁻¹ (≈129 meV).