Enhanced dual state emission from tri- and tetraphenylethene-substituted pyrene-fused heteroacenes

We report the design, synthesis, and optoelectronic properties of the first tri- and tetraphenylethene (TPE) substituted pyrene-fused heteroacenes (PHAs). All TPE-PHA compounds were characterised by UV-vis, IR, MS, NMR, PL, and cyclic voltammetry. Notably, TPE-PHAs exhibited strong emission with photoluminescence quantum yields (PLQYs) of up to 82% in the solid states. In contrast, their PLQYs in dilute solutions are comparatively lower (Qf= 7−14%) than their solid states due to the rotation of TMS, TIPS and phenyl rotors, and completely quenched in the case of tetraphenylsilane groups on quinoxaline residues. The optoelectronic properties of these compounds are predominantly dictated by the non-planar nature of TPE and alkynylsilane moieties. These observations are supported by X-ray crystallographic studies and theoretical calculations. In contrast to previously reported pyrene-fused heteroacenes, the solid-state emission properties of TPE-PHAs displayed significant enhancements owing to their large intermolecular distance in solids, as observed in the single crystal analysis. We also demonstrated a structure-property relationship that will help to design new solid-state emitting materials while improving solution processability and luminescence properties.