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Azobenzene Imides Branches Synthesis Of Functional Materials And Their Luminescent Properties

Posted on:2008-01-31Degree:MasterType:Thesis
Country:ChinaCandidate:L LinFull Text:PDF
GTID:2191360215999981Subject:Applied Chemistry
Abstract/Summary:PDF Full Text Request
The properties and application of poly (amido amine) (PAMAM) dendrimers and its derivatives have been investigated extensively. Azobenzene and its derivatives are typical molecules showing cis-trans photoisomerization, and they have been attracted much interest for the viewpoint of fundamental photochemistry and their high potential in industrial applications. Hence, study in this area can profound the mechanism of azobenzene derivatives light-response structure character and photos peculiarity. Also providing theory directioning to molecule materials design. In this paper, photo character as well as other properties of azobenzenes function PAMAM derivatives has been extensively investigated by a variety of physicochemical methods such as UV-visible absorption,fluorescent spectra, fluorescent life, quantum yield and theoretical calculations. Based on these communication, we have also investigate the effect of intermingle with rare earth ions, transition metal, CF3SO3H acid and triethylamine.The results obtained have shown that: (1) The absorption spectrum contains abroad band at 290nm , which originates from not only the azobenzene aggregates but also theπ'π* transition of the trans azobenzene units. The absorption at 395nm extends to 450nm, where the forbidden n'π* transition of the trans isomer is located. The steady-state fluorescence spectrum exhibit both S2 fluorescence (395 nm) and S1 fluorescence (760 nm), this may be due to the fact that the peripheral chromophores of the different generations possessing different sterically crowded structure and conjugation, which in turn prevents the dendrimers from parallel arrangement and the cis-trans photoisomerization of azobenzene units. (2) The fact that donating or pulling electron of carboxylic acid and protonation of–OH function decreases the luminescence intensity of Gn in acidity, but appreciably enhance in alkalescence. Both of them showed pH dependence in fluorescence intensity. (3) The effect of the rare earth ions (Er3+, Eu3+, Gd3+, Nd3+, Tb3+, Yb3+) and transition metal Cu2+ upon the fluorescent intensity of generation polyamidoamine dendrimers with a peripheral azobenzene group have been systematically investigated. The fluorescence spectrum have been quenched both at 395 nm and 760 nm emission reveal that the metal ions act as the electron receptor cause quenching of the excited state of the fluorophore by PET , and UV-visible absorption hole the location but a strong ligand-to-metal charge-transfer (LMCT) transition centered at 300nm emerges, suggesting the metal ions and ligand form exciplex at ground state. The difference of quenching effect resulted from the different electronic shell of metal ions and their ionic radius. Lower generations of the dendrimers are highly symmetric and tend to existing in an open and extended form. In contrast, the higher generations present a three dimensional globular structure with a densely packed chromophore shell. Therefore, stronger signals of fluorescence quenching have been observed in higher generations. Finally, we further testify it by three-dimensional fluorescence spectra, from them we find the dendrimers excited state can be adjusted through changing the length of ligand branch and pH, importing the external species and so on. The results obtained reveal that the azobenzene derivatives are useful for the fluorescent probe techniques, light-driven switches, and image storage devices.
Keywords/Search Tags:Dendrimer, Fluorescent spectrum, Ultraviolet absorb spectrum, PET, Fluorescence quenching, The rare earth ions, Adjusting
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