Imidazole decorated dicyanomethylene-4H-pyran skeletons with aggregation induced emission effect and applications for sensing viscosity

Abstract

Two imidazole decorated 4-dicyanomethylene-2,6-dimethyl-4H-pyran (DCM) derivatives, namely ImDCM-1 and ImDCM-2, have been designed and synthesized, which show aggregation-induced emission (AIE) features in THF-water mixture due to inhibition of intramolecular rotation (water fractions 80% and 70% for ImDCM-1 and ImDCM-2, respectively). The further increasing water leads to fluorescence bathochromic-shift and enhancement of ImDCM-1, probably arising from variation in size and solubility of aggregates. In contrast, ImDCM-2 exhibits a distinct red-shift and further enhancement in emission with water fraction increasing from 70% to 80%, then the further increment of water induces decrease in emission, which may be ascribed to formation of J-aggregates, followed by size and solubility changes of aggregates. In addition, selective and sensitive fluorescence responses of ImDCM-1 and ImDCM-2 towards viscosity can be observed. Significantly, the low cell cytotoxicity as well as wide pH-independence (4.0–10.0) fluorescent response towards viscosity allow them to be utilized for tracing monensin-stimulated viscosity increase in living cells.