Molecular Design And Application Of Spiropyran-based Colorimetric Probe Toward Ion Detection: A Theoretical Study

Spiropyran and spirooxazine derivatives are an important class of organic photochromic materials in the family of photochromic materials,and have been widely reported as cyanide ion（CN^-）detection probes in the fields of environment and medicine due to their advantages of simple execution,high selectivity,high sensitivity and short response time.The design of spiropyran colorimetric probes with high sensitivity,high selectivity and stability has become a research hotspot for researchers.In this thesis,The density functional theory（DFT）and time-dependent density functional theory（TD-DFT）was used to calculate the geometric structure,frontier molecular orbital,absorption spectrum,surface electrostatic potential,charge transport properties,and the microscopic mechanism of CN^-detection for the the spiropyran/spirooxazine type cyanide ion colorimetric probe molecules.Our study could offer a multi-scale guideline on the design of spiropyran-type colorimetric probes for cyanide ion detection.The thesis contents are as follows:1、Molecular simulation study of spiropyran cyanide ion detection probeSpiropyran-based derivatives are widely used for highly selective colorimetric detection of cyanide ion.DFT and TD-DFT were adopted to calculate electronic strcture,absorption propetites,density of state,and molecular mechanism toward cyanide sensing for 6-(2-（1-（2-hydroxyethyl）-3,3-dimethylindole-2-ylideneethylidene）-2-（hydroxymethyl）-4-nitrocyclohexane-2,4-dien-1-one（MC）,6-（2-（1-（2-hydroxyethyl）-3,3-dimethylindole-2-ylidene）ethylidene）-2-（hydroxymethyl）-4-nitro-3-（（4-nitrophenyl）diazenyl）cyclohex-2,4-dien-1-one（MC-1）and the newly designed 6-（（1-（2-hydroxyethyl）-3,3-dimethylindole-2-methylene）imino）-2-（hydroxymethyl）-4-nitro-3-（（4-nitrophenyl）diazene）cyclohex-2,4-dien-1-one（MC-2）and the corresponding post-CN^-addition molecules（MC-CN^-,MC-1-CN^-,MC-2-CN^-）.These results show that the absorption wavelength changes significantly after the introduction of CN^-.Compared with theπ-π*transition for the open-ring structures（MC,MC-1,and MC-2）,the transition mode of the molecular absorption wavelength after the introduction of CN^-is intramolecular charge transfer andπ-π*transition for the MC-CN^-,MC-1-CN^-,and MC-2-CN^-.Meanwhile,the newly designed SP-2/MC-2 exhibits excellent stability and absorption characteristics.This study provides reasonable theoretical guidance for the design of high-performance CN^-probes.2、Molecular simulation study of cyanide ion detection probe containing BODIPY donor and spiropyran acceptorThe BODIPY donor-Spiropyran acceptor system utilizes the principle of fluorescence resonance energy transfer（FRET）to detect cyanide ions.DFT and TD-DFT were used to study the substituent effects on the FRET and absorption wavelength forthe BODIPY donor and spiropyran acceptor system.For the spiropyran-based acceptor,the H on the benzene ring of MC-A1 indoline were substituted by CH₃/OCH₃ groups.The spectroscopic analysis show that the emission spectrum of BODIPY donor overlaps well with the absorption spectrum of CH₃/OCH₃ substituted spiropyran acceptor,and the absorption wavelength of spiropyran acceptor molecules is redshifted due to the introduction of electron-donating groups.At the same time,the electronic structure and absorption properties of the spiropyran-based molecules before and after the introduction of CN^-have revealed that the CH₃/OCH₃-substituted spiropyran can be used as a better cyanide ion detection probe.This study provides theoretical guidance for the design of highly stable donor-acceptor cyanide ion detection probes for spiropyran receptor molecules.