Raman spectroscopy as a probe of molecular order, orientation, and stacking of fluorinated copper-phthalocyanine (F16CuPc) thin films
Article first published online: 10 JAN 2013
Copyright © 2013 John Wiley & Sons, Ltd.
Journal of Raman Spectroscopy
Volume 44, Issue 4, pages 597–607, April 2013
How to Cite
Cerdeira, F., Garriga, M., Alonso, M. I., Ossó, J. O., Schreiber, F., Dosch, H. and Cardona, M. (2013), Raman spectroscopy as a probe of molecular order, orientation, and stacking of fluorinated copper-phthalocyanine (F16CuPc) thin films. J. Raman Spectrosc., 44: 597–607. doi: 10.1002/jrs.4231
- Issue published online: 10 APR 2013
- Article first published online: 10 JAN 2013
- Manuscript Accepted: 8 NOV 2012
- Manuscript Revised: 7 NOV 2012
- Manuscript Received: 30 JUL 2012
- Raman tensor;
- vibrational Davydov splitting;
- organic semiconductor
We report Raman scattering measurements on azimuthally ordered thin films of F16CuPc, prepared by organic molecular beam deposition on A-plane sapphire substrates. The observed peak frequencies have been compared both to the results of a model calculation for the vibrational modes of the free molecule and to those reported by other authors in related materials. This analysis provides a plausible identification of the modes responsible for the strongest spectral features. Detailed evaluation of the spectra reveals that some observed modes, which correspond to vibrations of the macrocycle inner ring, largely retain the intramolecular character and their polarisation properties can be used to study the orientation and stacking configuration of the molecules. We provide structural parameters deduced either in molecular or crystal symmetry considering the simpler possibilities, i.e. a single column molecular stacking and a herringbone-like structure. The results suggest that the thicker and most ordered film is structurally close to the recently reported crystal organisation of bulk ribbon samples of this compound. The crystalline quality of the ordered films is mainly reflected in some other Raman peaks which are related to the motion of peripheral atoms and dominate the high wavenumber part of the spectra. These modes are affected by intermolecular interactions inducing Davydov splittings that are unequivocally identified by the observed Raman selection rules. The performed analysis also provides quantitative estimates of the degree of in-plane ordering. Copyright © 2013 John Wiley & Sons, Ltd.