A double heterohelicene composed of two benzo[b]phenothiazine exhibiting intense room-temperature circularly polarized phosphorescence

Abstract

In this work, we report a novel double N,S-hetero[5]helicene composed of two benzo[b]phenothiazines (2) that exhibits long-lived circularly polarized room-temperature phosphorescence (RTP). Compared with the previously reported N,O-analogue composed of two benzo[b]phenoxazines (1), 2 emitted more intense phosphorescence with a longer lifetime than 1 in a frozen solution at near liquid nitrogen temperature and even at room temperature when doped in a β-estradiol matrix. The intense and long-lived phosphorescence of 2 was fully explained by theoretical calculations. The optical resolution of 2 was successfully achieved, and the chiroptical properties of 2 were investigated. We found that 2 doped in a matrix exhibits strong dual circularly polarized luminescence originating from fluorescence (|g_CPL| = 1.7 × 10⁻²) and long-lived phosphorescence (|g_CPL| = 5 × 10⁻³, lifetime of 0.16 s, and Φ_p of 30%) at room temperature. 2 is a very rare example of a purely-organic helicene that exhibits long-lived circularly polarized RTP from a non-aggregated state.