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Orientation of Nonplanar Molecules in Polycrystalline Layers from Infrared Spectra: Core-Chlorinated Naphthalene Tetracarboxylic Diimides

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journal contribution
posted on 21.02.2016 by Robert Lovrinčić, Jens Trollmann, Carl Pölking, Jan Schöneboom, Christian Lennartz, Annemarie Pucci
By means of infrared spectroscopic ellipsometry in the range of 350–5000 cm–1, the anisotropic dielectric functions of dichlorinated naphthalene diimide with fluoroalkyl chains (NDI-F), a novel high-performance n-type organic semiconductor, thin films were determined with high precision. Films of varying thicknesses (between 5 and 60 nm) evaporated in vacuum or spin coated from solution on different silicon wafers can all be described by the same anisotropic vibrational susceptibility, indicating weak dependence of the molecular orientation on processing procedure and film thickness for this material. It is shown how to determine the predominant molecular orientation by thorough comparison of ellipsometric measurements with calculations based on density functional theory. The method used additionally reveals subtle discrepancies between experiment and single molecule calculation which certainly arise from intermolecular interaction.