Study On ESIPT Reaction In The Branched Organic Dyes

Excited state intramolecular proton transfer(ESIPT) is one of the most important basic process in nature and life, and so it draws people’s considerable attentions. It is the research focus on organic photochemistry, photophysics and photobiology.Ortho hydroxy-imino segment is the typical chemical part which can undergo ESIPT reaction. To develop enlarged organic molecules with proton transfer segments through chemical covalent bond, which is conducive to ESIPT reaction. There is a saying that the insertion of π-conjugation units are not conductive to ESIPT reaction in organic chromophore. It is considered that the potential energy barrier of the internal proton transfer in the excited state can increase with the increase in the molecular size.Therefore, how to through the national molecular design, which can make the compounds occur ESIPT reaction, and appropriately increase the molecular weight for application, and that’s the focus of this thesis.In this thesis, a series of compounds which contain π-conjugation units bearing with single or double hydroxy-imino groups and the corresponding chromophores have been investigated. Furthermore, the effective action of intramolecular hydrogen bonds on ESIPT reaction has been studied as well. And try to use these chrmophores in metal ion recognition, such as Zn2+ indicator. The main contents of this thesis are as followings:①Based on the tunablity and control of chemical structures, various chromophores containing single or double hydroxy-imino groups the corresponding chromophores were synthesized(C1~C18). They were characterized by melting point, NMR, X-ray.The single crystal of C1, C2, C7, C11 were obtained by diffusion process, the structures were analyzed by X-ray.②The chemical structures of C1~C18 were characterized by NMR. Comparing the chemical shift of-OH- and-NH- between the target compounds C1, C3, C7 and the reference compounds C2, C4, C5, C6, C8,it proves that the hydrogen bonding between the hydroxyl and imino in C1, C3, C7 is effective. The compound C3 possesses more intensive intramolecular H-bonding effect than compound C1 does, as there is the same two armed salicylidene methylamine moieties in compound C3.③The probability of ESIPT reaction of compound C3 is bigger than that of compound C1, and it shows that the ability of an organic chromophore with thebranched structure having ESIPT reaction is bigger than that of single-stranded structure.The molecular geometry optimization shows that two transition states from enol to keto are formed in compounds C3 and C7, and it suggests that they could undergo internal proton transfer in excited state step by step.④The absorption and fluorescence spectra and the two-photon induced fluorescence spectra show that the chromophores with o-hydroxyl-phenyl-imino can undergo ESIPT reaction. In contrast, ESIPT reaction can not occur in the chromophores with p-hydroxy-phenyl-imino or o-hydoxy-phenyl-amino groups. It means that ESIPT reaction has been closely related to the substituted position of OH and C=N groups.⑤In DMF, Zn2+ion is recognized by compounds C7 、 C9 or C11 through the efficient enhancement of normal emission. OH and C=N are important to form coordination structure with metal ion. There is excellent the linear correlation relationship between the emission intensity and the concentration of Zn2+, while it is below 10 μM, and so it can be used in quantitative determination of Zn2+.