Study On The Properties And Responsive Mechanisms Of Novel Organic Two-photon Fluorescent Molecular Probes

Nonlinear optics is generated in the process of strong field laser interaction with the medium,and it has received extensive attention of researchers because its special effects differ from the ordinary optics.Two-photon absorption is an important nonlinear optical phenomenon.It has a wide application prospect in the fields of chemistry,biology,physics and materials science,especially in two-photon fluorescence microscopy.It is becoming more and more important to find new materials with excellent nonlinear optical properties.Compared with the inorganic materials,the organic molecular materials have attracted more and more attention because of their advantages such as good flexibility,wide response band,convenient cutting and so on.The two-photon fluorescent molecular probe can successfully realize the imaging and localization of small molecules / ions in the body,making it an important research tool in the field of biological sciences.At present,the experimental researchers have successfully designed and synthesized a large number of two-photon fluorescent molecular probes for the detection of different particles,but the relevant theoretical research work is still very little.Meanwhile the responsive mechanisms of many probe molecules are not clear,which need more theoretical calculations for in-depth analysis.We select two kinds of two-photon fluorescent probes that can detect important active oxygen species and active sulfur species in vivo.We use quantum chemical calculation method and combine density functional theory with response function theory to study the photophysical properties(including single-photon and two-photon absorption properties,fluorescence emission properties,etc.)of the two kinds of probes,and analyze the responsive mechanisms of the probe molecules.The specific research contents and results are as follows: 1 Hypochlorite-targeted two-photon fluorescent molecular probesTwo novel water-soluble hypochlorite two-photon fluorescent molecular probes,HCH and HCM,are investigated by using time-dependent density functional theory in combination with response theory.The changes of light absorption and light emission properties of the probe molecules before and after reacting with Cl O-are discussed in detail,and the detection property and responsive mechanism of probe molecules are analyzed theoretically.The theoretical results show that the optical properties of the two probes are changed a lot after reacting with Cl O-.Moreover,the corresponding absorption and emission peak positions are obviously blue shift and the fluorescence gain signal is enlarged.It is also found that the probes have large two-photon cross sections.And in the presence of Cl O-,the values of two-photon cross section of the molecules are increased significantly.Therefore both HCH and HCM can be good two-photon fluorescent probes for sensing Cl O-.By analyzing the molecular Mulliken charge population of the two probes and their corresponding products,the responsive mechanisms of the probes are theoretically confirmed to be C=N isomerization.2 Polysulfide-targeted two-photon fluorescent molecular probesOn the basis of the first principle,light absorption and light emission properties of the two probe molecules for recognizing H2 Sn are studied theoretically.The two probe molecules have the same recognition groups but the different fluorophores.In order to make the calculation results more realistic,the polarized continuous model is used to deal with influence of the solvent environment on the photophysical properties of the probes.The results show that the addition of H2 Sn makes the optical properties of the probe molecules change obviously.The emission intensity of the molecules before the reaction is very little and the molecules are almost non-fluorescent.After the reaction,the emission intensity increases significantly,which makes the fluorescence intensity increase sharply.At the same time,two-photon absorption cross-sections of the probes become larger after reaction with H2 Sn.By comparison,Pro2 molecule has a larger absorption cross section and it can be a better two-photon fluorescent probe.In addition,by analyzing the distribution of frontier molecular orbitals and charge transfer,the responsive mechanism of the two probe molecules is obtained as the combination of photon-induced electron transfer mechanism with intramolecular charge transfer mechanism.This thesis is divided into six chapters.The first chapter is an overview of nonlinear optics.The second chapter shows the structure,responsive mechanism,and research progress of two-photon fluorescent molecular probe and so on.The third chapter gives the theoretical basis and calculation method of this thesis.In the fourth and fifth chapters,two kinds of two-photon fluorescent molecular probes,which are used for the detection of hypochlorite and polysulfide,are calculated and discussed.The responsive mechanism is identified by analyzing the change of the optical properties of the probe molecules before and after reacting with guest species.The last chapter summarizes the contents of this thesis and looks forward to future research prospects.