Theoretical Study Of Two-photon Fluorescence Probe For Cysteine Based On Coumarinocoumarin

Because fluorescent probes can be used for simple,fast and efficient real-time localization of analytes for detection and analysis.Therefore,fluorescent probes have unique advantages in biological and chemical analysis and detection,especially in the field of biological tissue medicine research,and have become scientific research tools for efficient research and analysis.Compared with one-photon fluorescent probes,two-photon?TP?fluorescent probes have become the current trend in the field of fluorescent probes due to their high spatial resolution,deep tissue imaging,and accurate positioning.At the same time,the disadvantages of light damage,light interference and photo-bleaching caused by one-photon fluorescent probes are avoided.Therefore,the research of TP fluorescent probes has important academic significance and good application prospects.So far,fluorescent probe molecules with ideal two-photon absorption?TPA?properties can be rarely applied in practice.In the final analysis,the research on TP fluorescent probes is not enough,and the theoretical basis of TP fluorescent probes needs to be improved.In-depth discussion of the theoretical basis of TP fluorescent probes and the design and development of new bio-fluorescent probe molecules with good properties of TPA that can be practically used to detect various identifiers have become one of the hot topics of current research.Based on a large number of literature surveys,it has been found that bio-thiols play an important role in prokaryotes and eukaryotes.As thiol-containing compounds naturally occurring in bio-thiols,cysteine?Cys?,homocysteine?Hcy?and glutathione?GSH?play a key role in the protein reaction process in cells.Among them,low molecular weight Cys is an essential amino acid in human protein synthesis,and also plays a vital role in redox balance,detoxification and metabolism.If its levels are abnormal,it can cause edema,liver damage,slow growth,muscle relaxation and obesity,physical weakness,hair loss,and hematopoietic function.Therefore,it is urgent to develop a method for detecting bio-thiol with excellent performance.In this thesis,first-principles quantum chemical calculations are used to systematically study the photo-physical properties of cysteine TP fluorescent probes and related recognition mechanisms.In order to achieve effective recognition of cysteine,we have designed several new types of coumarinocoumarin based on the excellent fluorescence properties of coumarin molecules and the experimental fact that sporadic coumarinocoumarin can be used as a fluorescent probe,the recognition of which depends on enabled photo-induced electron transfer?PET?and intramolecular charge transfer?ICT?mechanisms toward cysteine.For the probe molecules and the corresponding product molecules,we first calculated the rates of the two processes,electron transfer?ET?and charge transfer?CT?,and successfully explained the experimental phenomena from a kinetic perspective.Then,their TP properties were predicted theoretically,and their structure-property relationships were studied systematically.The results show that the transition dipole moments of coumarinocoumarin and monomer coumarin are significantly different,which allows the coumarinocoumarin to break the limit of the linear increase in the dipole moment vector of the monomer coumarin in the direction and magnitude.Moreover,the coumarinocoumarin derivatives have a large conjugate plane,and most likely have a large two-photon absorption?TPA?cross-section value,so they may become excellent TP fluorescent materials.At the same time,according to the relative directions of the dipole moment vectors of different transitions of the molecules studied,a three-state model is used to analyze the determinants in the TPA process.The study found that the magnitude of the two-photon cross-section value(?^T_max)depends on the state dipole moment(?^{j j}(?ⁱⁱ))of the transition channel and the transition dipole moment(?⁰ⁱ)of the coherent channel.Through the above research,we propose that?1?the length of the?conjugated chain can be increased along the 7-position of the coumarinocoumarin skeleton;?2?extend the?conjugated chain along different paths to change the state dipole moment of the transition channel of the target molecule and the direction of the transition dipole moment vector of the coherent channel to improve the TPA cross-section values of the probe molecule.Moreover,maximum TPA wavelength can be achieved in the range of 700-1000 nm for designed probe molecules,effectively avoiding factors such as the self-fluorescence of biological tissues and background interference.CCy-1-OH^CCy-3-OH and CCy-7-OH molecules are designed to be excellent candidates for TP fluorescent probes.We hope this research can provide useful theoretical basis for cysteine imaging research.