Linearly polarized luminescence of polyyne molecules aligned in PVA films

Size-selected linear sp-carbon chain molecules of hydrogen-capped polyyne C12H2 are dispersed in stretched polyvinyl alcohol (PVA) films to align them along the direction of stretching of the film. The order parameter for anisotropic molecular orientation is determined from the angular dependence of UV absorption band intensities using linearly polarized incident light. Phosphorescence spectra at cryogenic temperature of 20 K of aligned C12H2 polyyne molecules in the stretched PVA film exhibit anisotropic properties, namely linearly polarized luminescence (LPL). Molecular orientation is modeled by the |cos⁡θ|N distribution of linear molecules to simulate angle-dependent polarized optical emission intensities. The ensemble of aligned polyyne molecules is demonstrated to be an ideal molecular system for consideration of linear dichroism in LPL as well as in photo absorption.