Aggregation‐induced‐emission‐active carbazolyl‐modified benzo[4,5]thiazolo[3,2‐c]oxadiazaborinines as mechanochromic fluorescent materials

Two highly emissive donor‐acceptor type organoboron dyes, based on carbazole donor and benzothiazole‐fused oxadiazaborinine acceptor, were designed and synthesized. The compounds demonstrated high positive solvatofluorochromism in solutions, caused by intramolecular charge transfer. Such carbazolyl‐containing N,O‐chelated organoboron dyes exhibited aggregation‐induced emission properties: in tetrahydrofuran/water mixture with a high water amount, they formed highly emissive nanoaggregates. Both materials demonstrated efficient solid‐state emission in the crystalline and thin film state (PLQY of up to 48 %), as well as significant mechanofluorochromic properties (Δλem=30–38 nm). Moreover, a compound with unsubstituted carbazole unit was isolated as two distinct crystalline polymorphs with different photophysical properties.