A binaphthalimide motif as a chiral scaffold for thermally activated delayed fluorescence with circularly polarized luminescence activity

Abstract

This work describes the synthesis, photophysical and chiroptical properties of a new carbazole-naphthalimide donor–acceptor pair designed to induce circularly polarized thermally activated delayed fluorescence (CP-TADF). A monomeric achiral variant is compared to the dimeric target designed with a binaphthalimide core. TD-DFT calculations performed with the TPSSh basis set suggested that while the monomeric form should be purely fluorescent, dimerization is expected to trigger the emergence of TADF. Time-dependent and temperature-dependent spectroscopic analyses proved that while the monomeric species did not display any delayed emission because of a wide singlet-triplet (ΔE_ST) energy gap of 0.46 eV, the dimerization had a tremendous effect reducing the ΔE_ST to 0.1 eV enabling TADF emission with a 31% photoluminescence quantum yield in toluene. The enantiomers exhibited high performance CPL at room and low temperature with a dissymmetry factor up to 6 × 10⁻³ for TADF at room temperature and 5.2 × 10⁻² for phosphorescence at 77 K. The chiral target displays various solid-state packings from the yellow phase (YP), including crystals, aggregates and gels, to an orange/red phase (OP). The transition from YP to OP can be achieved by applying mechanical stress.