Near-infrared surface-enhanced Raman scattering of ultrathin films of CnAzoNaph(1,4)CmN+Br- (n = 7, 10, 12;: m = 4, 6)

被引:32
作者
Wu, YQ [1 ]
Zhao, B
Xu, WQ
Li, GW
Li, BF
机构
[1] Jilin Univ, Key Lab Supramol Struct & Spect, Changchun 130023, Peoples R China
[2] Kwansei Gakuin Univ, Sch Sci, Dept Chem, Nishinomiya, Hyogo 6628501, Japan
关键词
D O I
10.1021/la9803169
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Near-infrared (NIR) Fourier transform (FT) Raman spectra have been measured for a series of 4-[4'-[[(4 "-alkyloxy)phenyl]azo]naphthyloxy] alkyltrimethylammonium compounds [C(n)AzoNaph(1,4)CmN+Br-] in a solid state, in a cast film on a CaF2 plate, and in dipping films on etching silver foils and for one- and three-layer Langmuir-Blodgett (LB) films of C(10)AzoNaph(1,4)C4N+-sodium dextran sulfate (SDS) on a CaF2 plate and etching silver foils. The one-monolayer LB film on the silver foil shows much more intense Raman signals than the 75-layer film on the CaF2 plate, showing a great surface-enhanced Raman scattering (SERS) effect for the LB film on the silver foil. Since SDS plays a role as a spacer C(10)AzoNaph(1,4)C4N+ is not directly adsorbed on the silver surface. Therefore, the strong SERS effect for the LB films of C(10)AzoNaph(1,4)C4N+-SDS may be explained by an electromagnetic mechanism. The one-monolayer dipping film of C(10)AzoNaph(1,4)C4N+Br- on the silver foil shows about 10 times stronger Raman signals than the one-monolayer LB film and the spectral intensity pattern is quite different between the dipping and LB films. It is very likely that the direct adsorption of C(10)AzoNaph(1,4)C4N+Br- on the silver foil gives a much stronger SERS effect for the dipping film. The different intensity pattern between the two kinds of films may be due to the differences in the molecular orientation and/or aggregation in the films. The dipping film of C(7)AzoNaph(1,4)C4N+Br- yields a much smaller SERS enhancement factor. The alkyl tail is too short to have well-organized molecular aggregation and/or orientation in the film, and the enhancement factor may be sensitive to the molecular aggregation and/or orientation in the film.
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页码:1247 / 1251
页数:5
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