Searching for Suitable [Cu(N^N){(PPh₂)₂C₂B₉H₁₀}] Thermally Activated Delayed Fluorescent Dopants: Optimization of the...

The quantum yield of thermally stable, neutral [Cu(dppnc)(R-tbz)] complexes, where dppnc = {(PPh₂)₂C₂B₉H₁₀}^-, exhibiting thermally activated delayed fluorescence (TADF), has been optimized to values as high as 42% through strategic variation of the substituent on the thiazolyl unit of the Htbz (2-(4-thiazolyl)benzimidazole) ligand. A comprehensive analysis of structural features, geometric distortion, steric hindrance, and ΔE(S₁-T₁) and E(T₁) reveals that maximizing quantum yield requires the razionalization of other nonradiative routes, in addition to those affecting TADF. This study provides key insights for the rational design of highly emissive copper-based complexes. In contrast, the use of the analogous neutral diphosphane [dppcc = (PPh₂)₂C₂B₁₀H₁₀], forming the corresponding cationic [Cu(dppcc)(R-tbz)]⁺ complexes, allows modulation of the emission energy but results in significantly lower quantum yields.