Theoretical Insights on the Sensing Performance for Newly-synthesized Two-photon Fluorescent NH Probes Based on Spirobifluorence.

The development of fluorescent probe for hydrazine (NH) detection has attracted much attention due to the important role of NH plays in the fields of medicine, agriculture, biology and environments. In this paper, the optical properties and water solubility of two novel two-photon fluorescent molecular probes (Probe1 and Probe2) before and after the reaction with NH are studied by using the density function theory. The results show that electronic distribution and transition dipole moment of the probes are obviously changed after the reaction with NH, thus the optical properties of the molecules are influenced and the detection of NH are realized. In addition, photoinduced electron transfer processes for Probe1 and Probe2 in the presence of NH are theoretically characterized, which explains the experimental observations from the microscopic mechanism. Special attention has been paid on the analysis of the two-photon absorption for the probes with the absence and presence of NH by the response theory method. Both probes with good water solubility show large variation on the two-photon absorption cross section when reacts with NH. In particular, the two-photon absorption response of Probe2 is more obvious, so it possesses preferable two-photon fluorescence microscopic imaging ability. More importantly, the receptor effect on the sensing performances of the probes are demonstrated, providing a theoretical reference for the design and synthesis on more efficient two-photon fluorescence NH probes. Our study provides necessary information on the response mechanism of the studied chemosensors and helps to establish the relationship between the structure and optical properties of two-photon fluorescence NH probes.