Theoretical Study On Fluorescent Probes Of HBH、BPH And Naphthalimide Derivatives

As a technology that can detect target compounds in organisms by a harmless way,fluorescent probes are widely used in the detection of various metal ions and toxic gases in living cells and organisms.As a result,in recent years a large number of fluorescent probes with excited intramolecular proton transfer（ESIPT）,intramolecular charge transfer（ICT）,photoinduced electron transfer（PET）and fluorescence resonance energy transfer（FRET）mechanisms as response mechanisms have been designed and synthesized.However,the research on the fluorescence mechanism of fluorescent probe based on theory is incomplete.Therefore,in this paper,we study the reaction mechanism of several different types of fluorescent probes（HBH、BPH and naphthalimide derivatives）by using density functional theory（DFT）method and time-dependent density functional theory（TDDFT）method.Through the theoretical research on probes HBT-Hg and HBH,we obtained the fluorescent luminescence mechanism of probe HBT-Hg and the excited state intramolecular proton transfer process of probe HBH.Under the geometric optimization of ground state and excited state,the changes of bond length,bond angle and infrared spectrum of probe molecule were analyzed,and the strength trend of hydrogen bond in probe molecule HBH was obtained.In the scanning results of potential energy curve,we obtained the single fluorescence characteristics of probe HBH.In Chapter 3,we calculated the fluorescence quenching mechanism of the“open”fluorescent probe molecule BP and the FRET fluorescence luminescence mechanism of BPH.In the analysis of fluorescence properties,we calculated that the probe BP molecule does not emit fluorescence,but BPH emits fluorescence.This conclusion is consistent with the experimental phenomenon,which shows the reliability and rationality of our calculation level.Through the analysis of molecular orbital and electron excited state,we obtained the fluorescence resonance energy transfer mechanism of probe BPH.In Chapter 4,a series of 3-nitro-1,8-naphthalimide derivative fluorescent probes（Lyso FP,COFP,Nuc FP）,we obtained the fluorescence quenching mechanism of probes Lyso FP-NO₂,COFP-NO₂and Nuc FP-NO₂ and the fluorescence emission path of probes Lyso FP-NH₂,COFP-NH₂and Nuc FP-NH₂.In addition,our calculation results also show that the general fluorescence quenching mechanism of 3-nitro-1,8-naphthalimide derivatives should be the existence of dark nπ*state,involving the orbital transition from n orbital of nitro to LUMO orbital,resulting in fluorescence quenching.When replacing nitro with amino group will remove nπ*state and reduce the energy of LE state,so as to“turn on”the fluorescence.In short,the calculation level we selected in the three calculation systems is reasonable and reliable.The fluorescence mechanism of different types of fluorescent probes is described from the perspective of theory,which makes up for the lack of experimental explanation of the mechanism and corrects the wrong explanation of the mechanism in the experiment.