Synthesis and Photophysical Properties of Thiazole/Benzothiazole‐Fused Nonastarazines: Extending the Core and Tuning Emission via Positional Substitution

A serial of three-armed boron-locked nonastarazines (NSAs) peripherally fused with thiazole or benzothiazole rings have been synthesized via a two-step sequential reaction under mild conditions. Single-crystal x-ray diffraction reveals nearly planar π-skeletons, with the boron atoms deviating slightly from the ring plane and the boron-bound phenyl groups protruding above and below the plane to suppress π-π stacking and ensure good solubility. Compared to the previous pyridine-fused NSAs, thiazole/benzothiazole fusion significantly tunes the electronic structure. Introduction of electron-donating substituents (phenyl, thienyl) at the 5- or 6-position of the benzothiazole arms modulates the photoluminescence quantum yields (PLQYs) from 2.7% to 64.1%. Notably, 6-substitution produces consistently higher PLQYs than 5-substitution. This work expands the core chemistry of star-shaped B,N-doped arenes and establishes clear structure-property guidelines for efficient luminescence.