Polarization study of electronic transitions in molecules in a stretched PVA matrix using their projected three-dimensional vibrational space

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Abstract
A method is described for determining the direction of an optical transition in the chain molecules or guest molecules in a stretched polymer matrix with a quantitative elegance comparable to that of polarized single crystal spectroscpy (PSCS). The method consists in using the three‐dimensional vector (ray) space formed by the vibrational and electronic transition moments of the molecules. It determines the polarization ratios for four of these transitions: Three of them are linearly independent and constitute a monoclinic system of axes; the remaining one is the transition whose direction in the vibrational vector space of the molecules is to be determined. The method leads to the determination of an orientation parameter K that is described in terms of the molecular orientation distribution function of the relevant molecules in the stretched polymer matrix, without assuming any explicit form of that function. It has been applied to three aromatic molecules incorporated as guests in the PVA matrix and gives directions of electronic transitions in them that differ in most cases from those determined previously on the basis of assumptions regarding their molecular orientation distribution function in the stretched PVA matrix and the identity of their molecular orientation axis. These directions compare well with those obtained in mixed crystals using PSCS. Better agreement with SCF‐calculated theoretical results is also obtained.

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