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.