Spectroscopy with Polarized Light

In the gas phase or in isotropic hosts, such as liquids, polymers or glasses, the transition dipole moments of the guest molecules exhibit random orientations. In anisotropic systems, like crystals and stretched polymer films, there is usually a correlation between the orientation of the molecule and the geometry of the host matrix. The probability of electric dipole absorption depends on the square of the scalar product 

At room temperature (upper drawing) the average structure is planar. The orientation is given by the angle 0 between the molecular plane and the 6-axis. There are two possibilities 0 = 32.7° and 0 = -32.7°. 

Room Temperature Below Phase Transition (193 K) a-Domain  

M-axis Position M-axis Central ring Torsional angle 

As already mentioned in previous chapters, pentaceoe molecules substitute for p-terphenyl molecules. We assume that the pentacene molecule has the same orientation as the removed p-terphenyl (the short axis of the pentacene is aligned with the M-axis of the substituted p-terphenyl and their long axes are aligned) and that it is not strongly deformed. The transition dipole moment of the pentacene molecule introduced is oriented along its short axis. The different substitutional positions (Mi, M2, M3 or M4) of the crystal host cause a different solvent shift, for the four spec- 

---

A rigorous and complete mathematical treatment of the polarization of light and the interaction of light with oriented matter is outside the scope of this chapter. These subjects have been thoroughly dealt with before and can be found in a number of comprehensive texts [29-32] the reader is referred to the excellent book by Michl and Thulstrup [3] for a more detailed treatment of optical spectroscopy with polarized light. Here, a conventional, qualitative representation is given to establish the nomenclature and conventions to be used and to facilitate the understanding of the concepts presented. 

J Michl and EW Thulstrup, Spectroscopy with Polarized Light, 1st ed., VCH Publishers, New York, 1986. 

When spectroscopy with polarized light or other optical polarization measurements are performed the studied sample becomes one element of the optical train which transmits the beam from the radiation source to the detector. Four optical phenomena might take place in a sample sensitive to polarized radiation. We list them below together with their physical definition ... 

Michl J, Thulstrup EW (1986) Spectroscopy with polarized light. VCH Publishers Inc, New York Mierzecki R (1979) Acta Phys Pol A56 261 Miles HT (1964) Proc Natl Acad Sci USA 51 1104... 

Michl, J., Thulstrup, E.W. (1986), Spectroscopy with Polarized Light VCH Inc. New York. 

Chapter 1 describes the basics of electronic spectroscopy at a level suitable for nonspecialists. Specialized topics such as the use of polarized light are mentioned only briefly and the reader is referred to the monograph by Josef Michl and Erik Thulstrup, Spectroscopy with Polarized Light, pub-... 

J. Michl and E. W. Thulstrup, Spectroscopy with Polarized Light Solute Alignment by Photoselection, Liquid Crystals, Polymers, and Membranes, Wiley-VCH, Weinheim, 1997. 

Absorption and Emission Spectroscopy with Polarized Light... 

J. Michl, E.W Thulstrip, Spectroscopy with Polarized Light, Wiley-VCH, Weinheim 1986, p. 45. 

Michl J, Thulstmp EW (1986) Spectroscopy with polarized light. VCH, New York... 

Y. Won and R. A. Friesner (1988) in Structure of Bacterial Reaction Centers X-ray Crystallography and Optical Spectroscopy with Polarized Light, eds. J. Breton and A. Vermeglio (Plenum, New York), pp. 341-349. 

Spectroscopy with polarized light, Michl, J. Thulstrup, E.W. Eds. VCH Publishers New York, 1986. 

---