Spiropyran-Isoquinoline Dyad as a Dual Chemosensor for Co(II) and In(III) Detection

Spiropyran derivatives have been studied as light-regulated chemosensors for a variety of metal cations and anions, but there is little research on chemosensors that simultaneously detect multiple metal cations. In this study, a spiropyran derivative with isoquinoline, SP-IQ, was prepared and it functions investigated as a light-regulated sensor for both Co²⁺ and In³⁺ cations. A colorless nonfluorescent SP-IQ converts to a pink-colored fluorescent MC-IQ by UV irradiation or standing in the dark, and MC-IQ returns to SP-IQ with visible light. Upon UV irradiation with the Co²⁺ cation for 7 min, the stronger absorption at 540 nm and the similar fluorescence intensity at 640 nm are observed, compared to when no metal cation is added, due to the formation of a Co²⁺ complex with pink color and pink fluorescence. When placed in the dark with the In³⁺ cation for 7 h, the colorless solution of SP-IQ changes to the In³⁺ complex with yellow color and pink fluorescence, which shows strong absorption at 410 nm and strong fluorescence at 640 nm. Selective detection of the Co²⁺ cation with UV irradiation and the In³⁺ cation in the dark could be possible with SP-IQ by both absorption and fluorescence spectroscopy or by the naked eye.