Imidazobenzothiadiazole: A new multifunction dyes for mechanochromic luminescence, acid responsing and mitochondrial staining

To develop new luminophores, three imidazobenzothiadiazole (ImBTD) fluorescent dyes (4a, 4b, and 4c) have been successfully synthesized and characterized. Interestingly, the introduction of imidazole groups at the 5- and 6-positions of benzothiadiazole can effectively enhance the fluorescence in both solid and aqueous solution and lead to a fluorescence response to acid. Modification of different aromatic groups at position 4 and 8 of ImBTD can produce tunable mechanochromic luminescence (MCL), which has been studied by theoretical calculations, single crystal X-ray diffraction (XRD), powder XRD analysis, and differential scanning calorimeter (DSC). More importantly, the neutral dyes 4a-c show mitochondrial staining comparable to commercially positively charged dyes. As a novel multifunctional fluorescent dye, it has application value in the fields of solid-state fluorescence and biological imaging.