Molecular Ordering in Monolayers of an Alkyl-Substituted Perylene-Bisimide Dye by Attenuated Total Reflectance Ultraviolet—Visible Spectroscopy

• Published in: Applied spectroscopy 2005-10, Vol.59 (10), p.1248-1256
• Main Authors: Doherty, Walter J., Simmonds, Adam G., Mendes, Sergio B., Armstrong, Neal R., Saavedra, S. Scott
• Format: Article
• Language: English
• Subjects: ATR; Attenuated total reflection; Molecular orientation; Perylene; TECHNOLOGY; TEKNIKVETENSKAP
• ISSN: 0003-7028; 1943-3530; 1943-3530
• DOI: 10.1366/000370205774430918

Surface-relative orientational parameters were determined for monolayer films of N, N′-ditridecylperylenetetracarboxylic dianhydridediimide (C13-PTCDI) in terms of the relative electronic transition dipole strengths, providing a three-dimensional view of the absorption dipole distribution. In order to obtain a macroscopically ordered film, C13-PTCDI was deposited by (1) horizontal Langmuir–Blodgett (LB) transfer onto methyl- and phenyl-silanized glass, and (2) vapor deposition onto oriented films of poly(tetrafluoroethylene) (PTFE) on glass. Films of LB-deposited C13-PTCDI were found to be completely isotropic prior to annealing. After annealing, these films remained isotropic in the plane of the substrate while the out-of-plane anisotropy was significantly enhanced. In contrast, films of C13-PTCDI vapor deposited onto oriented poly(tetrafluoroethylene) (PTFE)-modified substrates yielded films with a high degree of both in- and out-of-plane anisotropy. Atomic force microscopy (AFM) images of both the LB- and vapor-deposited films show substantial differences in film morphology and long-range order. These results demonstrate that molecular orientation in C13-PTCDI films can be controlled by varying substrate surface chemistry and post-deposition processing.