VIBRATIONAL CHARACTERIZATION OF LANGMUIR-BLODGETT MONOLAYERS AND EVAPORATED-FILMS OF A BISPHENYLENE-SUBSTITUTED PERYLENE-3,4,9,10-TETRACARBOXYLIC ACID-DERIVATIVE

The vibrational spectra of a bisphenylene-substituted perylene–3,4,9,10-tetracarboxyiic acid derivative (BPTCA) in thin solid films and Langmuir-Blodgett (LB) monolayers have been studied with IR and Raman spectroscopy. The molecular spectra of BPTCA evaporated at monolayer coverage were obtained by using surface-enhanced resonant Raman scattering (SERRS) on Ag-coated Sn spheres. Evaporated BPTCA films did not show any signs of preferred molecular orientation and were physisorbed onto the Ag surfaces. Stable LB layers of BPTCA mixed with arachidic acid were prepared and transferred to glass and to glass coated with the SERS active surface. An edge-on molecular orientation of aBPTCA in the mixed monomolecular layer was identified from the SERRS spectra on Ag; the spectra indicated chemisorption and a well-defined metal-molecule interaction. SERRS of BPTCA detached from the surface was also obtained by inserting an LB spacer layer of fatty acid between the BPTCA and the Ag surface; evidence for the chemisorption disappeared in the spectra of the detached layer. © 1990, American Chemical Society. All rights reserved.