Theoretical Calculation Studys On The ICT And PET Mechanisms Of Several Fluorescent Probes

Fluorescent probes are widely used for the specific detection of various ions,reactive oxygen species?ROS?and other substances.The optical sensing properties of probe molecules are closely related to their geometrical and electronic structures.The theoretical calculation can reveal the photophysical properties of fluorescent probes at electronic level and provide theoretical basis for design of fluorescent probes.In this paper,density functional theory?DFT?and time-dependent density functional theory?TDDFT?methods were applied to study the recognition mechanism of fluorescent probes.The photophysical properties and luminescence mechanism of fluorescent probes were studied by analyzing molecular geometry,electron structure,excitation state,natural bond orbital?NBO?,natural transition orbital?NTO?and electron-hole.The main results are as follows:1.A BODIPY-based near-infrared ratio fluorescent probe BFClO reacts with NaClO to emit red-shifted fluorescence.The structure of the reaction product and the luminescence mechanism are not clear.The structure of the product was determined by theoretical calculations and the ICT mechanism was clarified.Four new structures with different electron withdrawing groups introduced at the 8-position of the benzene ring were designed and increased Stokes shifts were found.Among them,-COOH and-CN groups result the best effect.2.The fluorescence mechanism of three D-?-A fluorescent probe 6a-c?a=NO₂,b=H,c=CH₃O?containing pyrazole fluorescent parent for the detection of cyanide?CN^-?was studied.Theoretical calculations showed that the 6a-c probes are excited to the LE state and then falls back to the more stable ICT state by the internal conversion process.Emission fluorescence exhibits a large Stokes shift.When the recognition group in the probe reacts with CN^-,the D-?-A system is destroyed,resulting in fluorescence quenching.3.The fluorescence on-off properties and PET mechanism of DATTA-Eu³⁺fluorescent probe molecules for detecting NO were studied.Theoretical calculations showed that the excitation of terpyridine fluorophore induces the electron transition from HOMO to LUMO.Due to the HOMO orbital level of the recognition group o-diaminophenoxy is higher than that of the terpyridine,the PET process occurs,resulting the emission to be quenched.Therefore,FRET pathway is blocked and no characteristic fluorescence of europium can be formed.After the recognition group is specifically reacted with NO,its HOMO orbital level is reduced,and the PET process is prevented.Terpyridine in the excited state can transfer energy to Eu³⁺via FRET pathway,producing characteristic fluorescence of europium.