Circularly Polarized Electroluminescence of Chiral Copper(I) Complexes of 1,1’-Binaphthalene-Functionalized 1,10-Phenanthroline

This study is dedicated to the design and synthesis of novel yellow-emitting Cu(I) complex enantiomers, R/S-Phen-Cu-POP, where the Cu(I) center is chelated by chiral 1,1’-binaphthalene-functionalized 1,10-phenanthroline (Phen) and bis(2-diphenylphosphinophenyl)ether (POP). Photophysical characterization revealed that the quantum yield (Φ_em) of R/S-Phen-Cu-POP in CH₂Cl₂ solutions was only 1.4–1.6%, but it significantly increased to 73.0% (R) and 76.1% (S) in PMMA doping films. Circularly polarized luminescence (CPL) studies demonstrated solid-state photoluminescence asymmetry factors (g_PL) of R/S-Phen-Cu-POP were +8.5 × 10^–3 and −8.6 × 10^–3. Temperature-dependent emission spectra and lifetime studies identified a small singlet–triplet energy gap (ΔE_ST = 0.073 eV), which facilitates reverse intersystem crossing (RISC) from the triplet (T₁) to the singlet (S₁) state, thus leading to the transformation of phosphorescence at low temperature to thermally activated delayed fluorescence (TADF) at ambient temperature. Solution-processed organic light-emitting diodes (OLEDs) achieved a maximum luminance of 1270 or 1379 cd/m², a current efficiency of 31.8 or 30.3 cd/A, a power efficiency of 14.8 or 14.4 lm/W, and an external quantum efficiency (EQE) of 11.9% or 11.3% for R-Phen-Cu-POP or S-Phen-Cu-POP, respectively. Furthermore, the devices displayed efficient circularly polarized electroluminescence (CPEL) with electroluminescence asymmetry factors (g_EL) of +8.7 × 10^–3 and −8.0 × 10^–3 for R/S-Phen-Cu-POP.