The liquid crystal–linear dichroism (l.c.–l.d.) of organic molecules by a modulation technique. Part 2. The phenylthio and thiophthen chromophores studied by an ‘l. d. substitution approach’

Abstract

A new development of the l.c.–l.d. technique is presented. The correlation of the experimental measurements and the reduction equations, which display absorption components along the molecular axes, are reported in terms of the quantities recorded by the modulated techniques. To illustrate the application of l.c.–l.d. in assigning the polarizations of electronic transitions, two model applications to a high symmetry (phenylthio) and a low-symmetry (thiophthen) chromophore are presented. In order to characterise the polarizations of the electronic transitions detected, the orientations of the chromophore are variously modified on the basis of a ‘substitution approach’. New assignments of the transitions of the phenylthio chromophore are proposed. The l.c.–l.d. spectra of the thiophthen chromophore indicate a new band, previously unreported, and support published theoretical results.