Study on the photochromism, photochromic fluorescence switch, fluorescent and colorimetric sensing for Cu2+ of naphthopyran-diaminomaleonitrile dyad and recognition Cu2+ in living cells.

A well-designed naphthopyran-diaminomaleonitrile dyad (sensor 1) has been synthesized successfully, its molecular structure was well characterized by NMR and mass spectrometry. Sensor 1 exhibits excellent photochromic and photochromic fluorescence switch performance with reversible color change and good fatigue resistance upon alternating ultraviolet irradiation and thermal bleaching. In addition, sensor 1 displayed excellent fluorescent and colorimetric sensing ability towards Cu2+ ions with high selectivity and sensitivity. The addition of 5.0 equiv. of Cu2+ ions into sensor 1 (1 × 10-5) in CH3CN solution significantly quenched the fluorescence of sensor 1 by 80.0%. Furthermore, the addition of Cu2+ ions also caused the complete disappearance of the absorbance band at 350-450 nm in absorbance spectra of sensor 1 and accompanied by the distinct color change form yellow to colorless. Job's plot, mass spectrometry, 1H NMR titration and DFT calculations proved that sensing performance was attributed to the formation of 1:1 sensor 1-Cu2+complexes. Sensor 1 can monitor the existence of Cu2+ ions in living cells via the fluorescence images. Sensor 1 showed great potential applications as chemosensor and photochromic materials.