BN‐Fused Polycyclic Heteroarenes Containing Thiopyran Moieties: Synthesis, Aromaticity, and Dual‐Chromic Behavior

BN-fused polycyclic heteroarenes have attracted extensive attention due to their distinctive structures and optoelectronic properties. However, the fusion of an azaborine ring on a six-membered thiopyran ring remains unexplored, limiting the chemical diversity and optical tunability of this unique material family. Herein, BN-embedded thiopyran derivatives with different conjugation lengths have been straightforwardly synthesized, and their photophysical properties, aromaticities, and dual-chromic behaviors have been systematically investigated. The successful incorporation of the thiopyran ring into BN-embedded heteroarenes endows the rigid molecules with a narrow optical band gap. Moreover, the BN-fused thiopyran derivatives exhibit dual-chromic behaviors in response to fluoride ions and protons. Unlike the fluoride ions coordinating to the azaborine rings, the protons are introduced on the cyclopenta[b]thiopyran moieties, as revealed by nuclear magnetic resonance spectra and theoretical calculations. Additionally, fluorination brings about the loss of aromaticity for the azaborine ring, while protonation induces the aromaticity enhancement for the thiopyran ring. Furthermore, dual-chromic pictures based on the BN-embedded thiopyran derivates are demonstrated. Overall, this work not only provides the first construction of BN-fused thiopyran derivatives but also develops new candidates for dual-chromic smart materials.