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 (Φem) 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 (gPL) 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 (ΔEST = 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 (gEL) of +8.7 × 10–3 and −8.0 × 10–3 for R/S-Phen-Cu-POP.