Abstract
Three novel spiro N-oxidized pyrrolidone-appended hemicyanine derivatives have been synthesized and characterized by 1H NMR, 13C NMR, UV–Vis and HRMS. The molecular structures of spirocyclic dye 2a and its opening-ring product 2aa have been determined by single-crystal X-ray diffraction analysis. The UV–vis spectra show significant solvatochromic behavior of three spirocyclic derivatives, especially in acidic and alkaline solvents. Spirocyclic dye 2a displays an excellent pH dependent behavior and responds linearly to extreme acidic conditions in the pH ranges of 1-4. The absorption spectra studies on opening-ring reaction reveal that acid and heat dual stimulation can induce opening-ring of 2a, which exhibits temperature-responsive linear in the range of 25–45 °C, behaving a colorimetric thermometer sensing. These properties provide the possibility for 2a-c to be used as stimulating response molecule switch.
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