A clear-cut experimental method to discriminate between in-plane and out-of-plane molecular transition moments

A new method to orient organic molecules, based on their absorption as guest of the crystalline nanoporous delta phase of uniaxially stretched syndiotactic polystyrene films, is presented. This molecular alignment method not only allows high degrees of guest orientation to be attained but also orients the planar guest molecules with their smallest cross section nearly parallel to the stretching direction (B) rather than perpendicular (A, as usual for absorption in amorphous polymeric phases). As a consequence, in-plane and out-of-plane transition moment vectors maximize their absorption intensities for light polarization nearly perpendicular and parallel to the stretching direction, respectively. Hence, simple linear dichroism measurements by polarized spectra can allow an easy and clear-cut discrimination between in-plane and out-of-plane guest transition moment vectors.