A series of D-π-A and A-π-A’ fluorescent probes were used to explore the influence of terminal groups on the properties of the hemicyanine probes

Based on the addition reaction of sulfur dioxide derivatives and C[dbnd]C, a series of D-π-A and A-π-A' fluorescent probes were designed by combining different electronic groups with benzoindole to study the influence of different end groups on the performance of such probes. When sulfite is detected, the fluorescence of ratio-type probe changes from red to blue, the fluorescence of turn-on probe changes from colorless to blue. The response time ranges from 90–300 s, the detection limit ranges from 10 nM–70 μM and the Stokes shift ranges from 1800 to 6800 cm⁻¹, all with high specificity. In addition, A2 has been successfully applied to cell imaging of endogenous sulfur dioxide derivatives.