Theoretical Investigation On The Luminescence Reaction Mechanism Of Cypridina Luciferin Analogues And Related Two-Photon Fluorescence Probe Material

Bioluminescene includes two classes of intracellular and extracellular luminescence. The extracellular bioluminescence usually is that the glands emitted from orgnisms contain some substances can luminesce. The extracellular bioluminescence has caused great interest of scientists. Cypridina can emit blue light in seawater, belongs to the extracellular bioluminescence. The cypridina bioluminescence has been a research focus due to its high bioluminescence efficiency and high sensitivity. But the chemiluminescence reaction mechanism of cypridina luciferin remains unclear, and especially, the theoretical research on it is scarce. Using Cypridina luciferin analogues to label cell nucleus or DNA as probe and monitor living cell and gene activity is a new research subject. Therefore, the thesis aims to study the chemiluminescent reaction mechanism of Cypridina luciferin, design a series of TPA probe materials which exhibit not only good fluorescence properties but also large two-photon cross section based on core structure of Cypridina luciferin. We calculated the ground-state geometries, the absorption spectra and frontier molecular orbitals, NBO analysis, and the transition state search by means of DFT method. Moreover, their optimized excited-state geometry, the emission spectra and fluorescence lifetime were obtained by TDDFT. The one- and two-photon absorption properties were calculated by using the Zerner's intermediate neglect of differential overlap (ZINDO) method and the sum of states (SOS) formula and the FTRNLO program compiled by our group. These calculations will play an important role in the study how to enhance the luminescence efficiency of cypridina luciferin analogues. And on the basis of above results, one can further explore high efficiency bioluminescence of cypridina luciferin and the design and synthesis of related TPA materials with good fluorescence efficiency and large TPA cross sections. The main contents of the thesis are summarized as follows:1. In order to explore the chemiluminescent reaction mechanism of cypridina luciferin, a series of cypridina derivatives were theoretically investigated in detail in the gas phase, DMSO, and diethylene glycol dimethy. These derivatives are obtained by replacing the 6-aryl with different group based on 6-aryl-2-methyllimidazo [1,2-a] pyrazin-3-(7H)-ketone rings. We discussed the geometry, bond length alternation, HOMO-LUMO gaps, electron extraction potentials and natural charge population through the key steps of chemiluminescence reaction. The results indicates that introducing the electron donating group result in better conjugated effect than electron-withdrawing group, and the interactions between electron-donating groups and central structure can be enhanced in solvent, which is ascribed to that the solvent enhances the electron donating ability and stability, and in turn facilitate MIP–→MIP·process in diglyme (DG). Form this point of view, introducing the electron-donating groups (especially indole as substituents) can increase the luminescent reaction rate of cypridina analogues and improve the efficiency of fluorescence.From the kinetic and thermodynamic perspective, we investigate the chemiluminescence reaction of pathes of (â… ) DT^ˉ→DT→¹AAP^*→hνand (â…¡) DT^ˉ→¹AAP^*ˉ→hν. The analysis of the activation energy of the reaction and the flurescence lifetime suggests that the DMSO solvent can improve the chemiluminescence of cypridina luciferin analogues and enhance the fluorescence efficiency, but DG solvent can increase the fluorescence efficiency of path (?).2. Whether cypridina luciferin analogues can be used as two-photon fluorescent probe? To resolve this problem, the fluorescence and two-photon absorption (TPA) properties of a series of pyrazine derivatives were investigated. The calculated results indicate that introducing styrene groups to 2, 3, 5-trisubstituted pyrazine derivatices can increase the conjugated effect and the TPA cross section values, which can enhance the TPA properties. Comparing their fluorescence properties, the fluorescent intensity (the excited state oscillator strength f_em) for the 2-styrene pyrazine derivatives and 5-styrene pyrazine derivatives are larger than the other substituents (acetylamino group and indole group) at the 2-site and 5-site of pyrazine core, and the f_em of 3-indole pyrazine derivatives is larger than that of 3-styrene pyrazine derivatives. Based on these results, we can conclude that the styrene group plays a positive important role in fluorescence of 2-, 5-sites of pyrazine derivatives. However, the series of 3-substituted pyrazine derivatives with indole group have also good fluorescence properties. Among the 2, 3, 5-trisubstituted pyrazine derivatives, 2-styryl-3-indolyl-5-styryl-pyrazine, 2-styryl-3,5-indolyl-pyrazine and 2, 3, 5- trisubstituted pyrazines have the good fluorescence properties and largly two-photon absorption(TPA) cross-section. The results above offer some important clues for the future investigation that cypridina luciferin analogues are to be as TPA fluorescence probe material.3. A highly sensitive two-photon fluorescent probes (TFP) for DNA detection attract great attention of many researchers. However, the binding form between two-photon fluorescence probe and DNA remains unclear. Thus, we theoretically studied a series of 3, 6-bis (4-vinylpydinium) carbazole derivatives (BMVC), and their dication (BMVC-C) and iodization (BMVC-I). The calculated results indicate that the N of 3, 6-vinylpyridinium carbazole and the 9-vinylpyridinium carbazole are all active sites, and the TPA spectra of the compounds with the different substituents at the active site are in the near infrared region (NIR), which makes them promising NIR two-photon image materials. In summary, the positions of 3, 6 and 9 are all the active sites when the studied molecules interact with DNA as two-photon fluorescent probes. The BMVC-C and BMVC-I molecules are more likely to combine with DNA as two-photon fluorescent probes.