Theoretical Study On Luminescence Response Mechanism Of Organic Fluorescent Probes

At present,organic small molecule fluorescent probes have become efficient research and analysis tools for their advantages of small size,accurate molecular weight,and good reproducibility.Compared with single photon fluorescence probes,two-photon fluorescence probes have become the current trend in the field of fluorescence probes due to its advantages of deep tissue imaging and accurate localization,while avoiding the disadvantages of light damage and light interference caused by single photon fluorescence probes.So far,the study of small molecule fluorescence probe is not deep enough,and the theoretical basis is still to be improved.It has become one of the hot issues in current research to explore the response mechanism of fluorescence probes and design and develop probe molecules with good properties that can be used in the detection of various recognizers.In this thesis,the photophysical properties and sensing mechanism of ophenylenediamines and boron difluoride fluorescence probes are systematically studied by means of first-principles quantum chemical calculation method,which lays a foundation for the development and utilization of a variety of biosensing probes in a wider range in the future.This thesis covers the following two main aspects:1.Theoretical characterizations of the two-photon fluorescent probes for NO detection:sensing mechanism,photophysical properties and protonation effects.In this study,we used a theoretical protocol that combines a polarizable continuum model,density functional theory and thermal vibration correlation function formalism to comparatively investigate the sensing mechanism,photophysical properties and protonation effects of two NO fluorescent probes(NINO and PYSNO)in water.Our findings reveal that the non-radiative property of NINO is due to the photoinduced electron transfer(PET)process with negative driving energy and the blocked fluorescence pathway with significant charge separation.In contrast,the poorly luminescent behavior of PYSNO is caused by the facilitated non-radiative decay process.The turn-on fluorescent responses of two probes upon exposure to NO result from the inhibition of the PET process and the integration of faster radiative and slower nonradiative decay processes,respectively.Currently,NINO has been successfully used to detect NO under two-photon microscopy,and our calculation results show that PYSNO is also an excellent two-photon fluorescence probe.The evidences of the protonation effects on the optical properties indicate that both probes can function effectively in practical lysosomal acidic environments.Our study opens a new avenue for understanding the mechanism and predicting the property of two-photon fluorescent probes for NO detection.2.Alkyl-cyclization effects on the twisted intramolecular charge transfer(TICT)process of β-diketone-boron difluoride based fluorescent probes: theoretical and experimental investigations.In this study,the optical physical properties and sensing mechanism of boron difluoride type polar response fluorescence probe were investigated by density functional response theory and density based solvation model.We found that with the increase of the polarity of solution,the absorption and emission wavelengths of molecules showed obvious redshift.The difference was that the fluorescence was quenched by the generation of TICT in the strongly polar solution of Probe 1,while the amino cyclization of molecular structure of Probe 2 and Probe 3 inhibited the generation of TICT on the basis of Probe 1.However,the fluorescence quantum yield still decreased slightly with the increase of solution polarity,indicating that these three fluorescence probes are good polarities responsive probes.In addition,the two-photon absorption capacity was studied in Dalton software,and it was found that all of them had large two-photon absorption cross sections,and the value of two-photon absorption cross sections gradually increased with the increase of molecular rigidity and conjugation degree.Therefore,all of them could be used as two-photon fluorescence probes with excellent performance.This work reveals the fluorescence sensing mechanism of the probe from the microscopic perspective and provides a powerful reference for the design of novel probe molecules in experiments.