Triazole functionalized 5,9-dioxa-13: B-boranaphtho[3,2,1-de] anthracene: A new family of multi-stimuli responsive materials

A series of N-heterocycle-tethered organoboranes B1-B5 were synthesized and fully characterized. All these compounds contain a robust 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (DBNA) core which plays a role as a Lewis acid site. Study of the different N-heterocycles as Lewis base moieties reveals that n-butyl-1H-1,2,4-triazolyl functionalized compounds (B1-B3) exhibit the dynamic switching of the intermolecular B-N bond in response to heat stimulus, leading to unusual reversible emission intensity enhancement at elevated temperature, while n-hexyl-1H-1,2,3-triazolyl attached compounds (B4-B5) only display thermal emission quenching behaviors. The different stimuli-responsive properties in solutions may be attributed to the position of the substituent alkyl chains which influence the torsion of the molecules, leading to different affinity of intermolecular B-N interactions. Single crystal X-ray diffraction analysis further confirms the dimeric species formation of B1-B3 in solid state. Furthermore, all compounds exhibit good mechanochromism.