Synthesis And Nonlinear Properties Of Novel Carbazole-based Pyridinium Salts

Nonlinear optics has attracted considerable attention due to the applications in telecommunications, optical information processing, optical computing and so on. In the past decades, a variety of nonlinear materials have been recognized including organic molecules, inorganic materials and organic-inorganic composites. There is more interest in the reasearch on organic nonlinear optical materials, because lots of organic molecules exhibit cheaper, extremely faster response, lower dielectric constant, easier to fabricate. According to molecules designing principles, the complicated performance of organic materials must be employed to achieve nonlinearity-transparency-thermal stability trade-off.Mostly, chromophores are designed to be one-dimensional charge transfer molecules containing donor (D) and acceptor (A) groups linked by aπ-conjugated bridge. For this kind of molecules, the increase in molecular hyperpolarizability always is accompanied by decrease in the thermal stability and optical transparency. So this paper investigates two-dimensional moleculesto solve this problem. Biologically, molecule of 3,6-Bis[2-(1-methylpyridinium)vinyl]-9-meth -yl-carbazole iodide was synthesized for stabilizing the quadruplex structure of human telomeric DNA sequence and inhibiting telomerase activity, which attracted increasing attention. In this manuscript, 3,6-Bis[2-(1-methylpyridiun)vi -nyl]-9-methyl-carbazole iodide and novel pyridimiun salt 1,8-Bis[2-(1-methyl -pyridini-um)vinyl]-3,6-Di-tert-butyl-9-methyl-carbazole iodideT were synthesiz -ed and characterized by IR, 1HNMR, 13CNMR, MS, UV and fluorescence spectroscopy. The first-order nonlinearity was obtained through solvatochromic method. The experiment results show that two chromophores synthesized display large first hyperpolarizabilities. TheβCT value of compound 9 reaches 407×10^-30469×10^-30esu and that of compound 11 reaches 493×10^-30548×10^-30 esu in five different solvents. Especially in methanol, TheβCT value of compound 9 reaches 469×10^-30esu and that of compound 11 reaches 548×10^-30esu. Simultaneously, two compounds have good transparency with maximum absorption wavelength for 446⁴58nm. Compared compound 9 with compound 11, the latter appears obviously blue shift in all five solvents. The fluorescence spectra exihits red shift from compound 9(570nm) to compound 11(580⁵90nm). TheβCT value of compound 11 is increased by 25% with increase in optical transparency and melting point by 20℃, which exhibits nonlinear-transparency- thermal stability trade-off.