Towards Fast Circularly Polarized Luminescence in 2‐Coordinate Chiral Mechanochromic Copper(I) Carbene Complexes

Abstract

A series of chiral mechanochromic copper(I) cAAC (cAAC=cyclic (alkyl)(amino)carbene) complexes with a variety of amide ligands have been studied with regard to their photophysical and chiroptical properties to elucidate structure-property relationships for the design of efficient triplet exciton emitters exhibiting circularly polarized luminescence. Depending on the environment, which determines the excited state energies, either thermally activated delayed fluorescence (TADF) from ^1/3 LLCT states or phosphorescence from ³ LLCT/LC states occurs. However, neither chiral moieties at the carbene nor at the carbazolate ligands provide detectable luminescence dissymmetries g_lum . An exception is [Cu(phenoxazinyl)(cAAC)], showing orange to deep red TADF with λ_max =601-715 nm in solution, powders and in PMMA. In this case, the amide ligand can undergo distortions in the excited state. This design motif leads to the first linear, non-aggregated CPL-active copper(I) complex with g_lum of -3.4 ⋅ 10^-3 combined with a high radiative rate constant of 6.7 ⋅ 10⁵ s^-1 .