Molecular Orientation and Structural Characterization of Ultrathin Films of C_(12)AzoNaph(1,4)C_6N-SDS Studied by FT-IR and NIR-SERS Spectroscopies

摘要

The orientation and structural characterization of the ultrathin film of azobenzene-containing amphiphilic compound, C 12AzoNaph（1,4）C6N +Br -, were studied in the present study. The compound can form a stable monolayer with sodium dextrin sulfate（SDS） by means of electrostatic interaction. Fourier-transform infrared（FT-IR） and near-infrared surface-enhanced Raman scattering（NIR-SERS） spectroscopies were used to study the orientation and characterize the structure of the Langmuir-Blodgett（LB） film and the dipping film. The FT-IR spectra indicate that the alkyl tail is nearly perpendicular to the substrate surface without any aggregation and adopts largely trans-zigzag conformation in the LB film. The NIR-SERS spectra demonstrate that the chromorphoric part in C 12AzoNaph（1,4）C6N +Br is also nearly perpendicular to the surface of silver substrate both in the dipping film and the LB film. A new "sandwiched system" model was designed to investigate the orientation and structural characterization of the chromophoric part in the multi-monolayer LB films on the non-SERS active substrate. The SERS mechanism of the "sandwiched system" is discussed in the present paper.