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Trends in Applied Spectroscopy   Volumes    Volume 7 
Abstract
Langmuir and Langmuir-Blodgett films of perylene tetracarboxylic derivatives: Molecular arrangement and surface enhanced spectroscopy
A. A. Zanfolim, C. J. L. Constantino, D. Volpati, N. P. W. Pieczonka, R. F. Aroca
Pages: 69 - 81
Number of pages: 13
Trends in Applied Spectroscopy
Volume 7 

Copyright © 2009 Research Trends. All rights reserved

ABSTRACT
 
It is well known that the molecular architecture plays an important role on the electrical and optical properties of thin films. In this work, the molecular arrangement of two perylene tetracarboxylic derivatives (C3H7-PTCD and C15H31-PTCD) forming Langmuir and Langmuir-Blodgett (LB) films is reported. The surface pressure-molecular area (π-A) isotherms for the Langmuir films showed that the PTCD with longer lateral alkyl chain reaches a higher pressure, indicative of stronger packing on the water surface. In addition, the mean molecular area values are evidence for the molecular arrangement of C3H7-PTCD with the planar PTCD moiety forming a smaller angle with the water surface. The Langmuir monolayers were transferred onto glass, Ag island films and Ge substrates forming LB films of 1 and up to 7 layers. The growth and molecular aggregation were analyzed by UV-Vis absorption spectroscopy. From FTIR vibrational analysis and using surface selection rules, it was extracted that the molecules are preferentially oriented with the PTCD moiety head-on in relation to the substrate surface. The surface-enhanced fluorescence (SEF) and surface-enhanced resonance Raman scattering (SERRS) spectra of Langmuir-Blodgett (LB) films deposited onto Ag nanostructures were also studied. It was found that the enhancement of the fluorescence (SEF) is a function of power density of the exciting irradiation. Chemical images from SERRS point-by-point mapping help to visualize the morphology of the LB films at micrometer scale.  The strong excimer emission observed for the LB films supports the molecular arrangement determined by UV-Vis (aggregation) and FTIR (molecular organization) techniques. Buy this Article


 
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