Polymorphism-dependent aggregation-induced emission of pyrrolopyrrole-based derivative and its multi-stimuli response behaviors

Bis(4-cyanophenyl)-4,4′-(2,5-diphenylpyrrolo[3,2-b] pyrrole-1,-4-diyl) dibenzoate (DPPCN) was synthesized and exhibited aggregation-induced emission properties. DPPCN was cultivated in different solvents getting three kinds of crystals, A, B and C. Crystals of A and B were respectively blue and cyan-blue emissive, while C was yellow-green emissive. They all displayed crystalline-induced emission behaviors. According to X-ray single crystal diffraction analysis, the intermolecular interactions account for restricted internal rotations , leading to fluorescence enhancement. The different kinds of co-effects of the solvent, intermolecular forces, molecular conformations and molecular packing modes endow DPPCN polymorphisms with multi-color emissions (from blue to yellow and up to 60 nm) and different fluorescence efficiencies. The fluorescence of A can be reversibly tuned by grinding and exposing to chloroform vapor with a 46 nm wavelength change. The crystal of C can blue shifted the fluorescence that matches with B upon fumed by chloroform for about 12 h and further blue shifted the fluorescence emission that matches with A when fumed by chloroform for about 24 h. Multi-color fluorescence tuning and switching is attributed to the nature of polymorphs, that is, a change of molecular conformation and intermolecular packing modes. The crystal of A also exhibited thermo-stimulus fluorescence switching behavior due to the co-crystallization with solvent chloroform. The properties of A show promising applications in temperature monitoring and volatile organic compound detecting devices.