Effect of transition moments and orientational behavior of dichroic dyes on the optical anisotropy of poly(vinyl alcohol) polarizing films

In order to examine the orientational behavior of dichroic dyes in terms of their structural characteristics and its effect on the optical anisotropy in stretched poly(vinyl alcohol) films, six azo dichroic dyes were synthesized and employed in dye/polarizing films. The dichroic ratios, order parameters and transition moments of the dyes were calculated. Molecular orbital calculation revealed that the transition moments of the dyes scarcely deviated from their molecular axes, resulting in minimal effect upon the optical anisotropy of the polarizing films. However, the dichroic ratios of the films increased as the angle of deviation of the dye molecular axes from the drawn direction of the host films decreased. In terms of the orientational behavior of the dyes, the number and position of hydrogen bonding sites had a significant effect on the alignment of the dyes when the host films were drawn. The orientational behavior of the dyes was more important in terms of the length of the dye molecular axes rather than their aspect ratios.