Figure3 Electron density difference between the S0 and S1
(a)C23-1 and (b)C23-4
The probe C23 could detect HSA and SO2 simultaneously due to the different fluorescence signal while binding with them. Michael addition reaction between probe C23 and SO2(HSO3-1) could saturate the rotational bonds in the C23 and stabilize the conformation which led to the strong fluorescence signal within the blue channel. To understand this mechanism, the conformation and electron excitation process of CS (C23 combined with HSO3-1) were analyzed using the same methods which were used for C23 before. The stable conformations of CS structure were reduced to two (CS-1 and CS-2 shown in Figure4). It can be clearly seen that due to the steric hindrance effect of HSO3 group, the rotational C-C bonds between the two rings in the probe were saturated and no longer rotated. This Michael addition reaction cut off the non-radiative pathway and led to the blue fluorescence signal within the electron excitation process of CS.