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Design, Synthesis and the Investigation of Optical Properties of New Conjugated Bride Pyridinium Salts

Author: SangYanKui
Tutor: TangJie
School: East China Normal University
Course: Organic Chemistry
Keywords: pyridinium synthesis Z-scan nonlinear refractive index nonlinear absorption fluorescence
CLC: O626.321
Type: PhD thesis
Year: 2010
Downloads: 223
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Abstract

Based on the previous research of our group, series of novel D-π-A type conjugate pyridinium salts were designed and synthesized for interesting optical properties. This dissertation contains three parts.1. By changing conjugated bridge bond, anion, N-alkyl of pyridinium, and substituent of electron-donating parts, thirty-one (D-π)2A and (D-π)3-A type novel conjugated pyridinium salts were designed and synthesized, and their structures were characterized by IR, UV, NMR and HRMS spectra.2. The structure of N-ethyl-2,6-bis[p-(N,N-dialkylamino)phenyl]pyridinium iodide was determined by single crystal X-ray diffraction. Compared to the corresponding N-methyl pyridinium, the conjugate chain planar at C2 and C6 position was deflected from the planar of pyridinium ring, which indicated that the substituent on N atom influenced greatly the product’s coplanarity.3. UV spetra indicated that intruding thienyl or phenyl bridge was favorable to the delocalization of electron, andλmax of the corresponding compound was obvious red-shifted. When compared of (D-π)3-A type pyridinium with the similar (D-π)2-A type compound, the Xmax was also red-shifted for the one more conjugated chain. Introducing allyl or benzyl group on the N atom of pyridinium made theλmax shift 15 nm to red when compared with that of N-alkyl compound. The alteration of anion did not influence the UV absorption wavelength. However, when the substituent on N of electron-donating group is phenyl, a 15 nm blue-shift was observed. 4. The nonlinear refractive index of all the compounds were tested by femto-second pulse Z-scan technique, and all the compounds showed self-defocusing effect.5. All the compounds were also determined by 50 femto-second pulse open-aperture Z-scan technique under 800 nm wavelengths, and the results displayed nice nonlinear optical absorption properties. The two-photon absorption coefficientβand absorption cross sectionσwere obtained by fitting the Z-scan curves.6. Introducing one more phenyl bridge to 2,6-bis[p-(N,N-dialkylamino)phenyl] pyridinium gave the compound 18, and its nonlinear optical absorption coefficientβand absorption cross sectionσwere up to 155×10-16 m/W,640 GM, respectively, which are 10 times higher than that of other compounds.1. A series of asymmetrical disubstituted functionalized 2,1,3-benzothiadiazole at 4,7-position were synthesized using o-toluidine as the starting material and after bromination, hydrolysis, and selective oxidation with IBX of 4-methyl-2,1,3-benzothiadiazole. This method provided an efficient route for preparation of asymmetrical disubstituted functionalized 2,1,3-benzothia-diazole blocks.2. Eight fluorescent intermediates, which containing a formyl group of coumarin, carbazole, phenothiazine were synthesized, and their structures were characterized.3. By condensation of the functionalized fluorophore with 4-methylpyridinium iodide or 2,6-dimethypyridinium iodide, twelve novel mono-substituted and di-substituted, bearing fluorescent group, D-π-A type pyridinium salts were obtained and their structures were characterized by NMR and HRMS.4. The optical properties of these pyridinium salts were preliminarily investigated by UV and fluorescence emission spectra. The mono-substituted pyridiniums exhibited nice linear absorption properties. Introducing electron-donor group improved obviously the electron delocalization ability, and the largest red shift ofλmax was 166 nm. Some of the di-substituted pyridiniums also showed good absorption properties. The preliminary fluorescence emission spectra displayed nice fluorescent emission properties, and these compounds may potential serve as fluorescent materials.The nonlinear optical properties of multi-ferocenyl substituted D-π-A type conjugated pyridinium salts, which were prepared in our group, were preliminarily studied by pico-second pulse open-aperture Z-scan technique.1. Six multi-ferocenyl substituted pyridinium salts, bearing different bridge bond, displayed nice reverse saturable absorption properties. UV spectra showed that the absorption wavelength shifted obviously to red with the conjugated chain growth, and the largest red shift is 50 nm.2. Eight multi-ferocenyl substituted pyridinium salts, containing different anion, showed nonlinear optical absorption properties, and five of them exhibited significant reverse saturable absorption properties. It is very interesting that the compounds, with ClO4- as anion, displayed extraordinary absorption properties.3. The alterations of pyridinium’s N-alkyl group led to the changes of the molecule’s symmetry which influenced significantly the compounds’ nonlinear optical properties. All the seven tested different N-alkyl pyridinium salts showed nonlinear absorption effect. Besides the reverse saturable absorption, conversion of saturable absorption to reverse saturable absorption and other nonlinear optical properties were also existed.

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