Molecular origins of optical dichroism of glassy and mobile systems as prepared by angular-dependent photoselection

A theory is outlined for the optical dichroism of a molecular system which had been rendered optically anisotropic by angular dependent photoselection of light. It is shown that in a glassy system the optical dichroism gives information on the components of the transition moments of absorption of the light used to monitor the dichroism, and an order parameter S = P 2 ≡ ⟨DJ 00⟩ for the orientation distribution of the molecules. In mobile systems it is shown that the dichroism, measured as a function of time, gives information on the time correlation function ⟨D 2 00(Ω(0))D 2*00(Ω(t))⟩ for the reorientation of the z-molecular axis. A method is proposed for studying molecular motion by transient dichroism of photoactive molecules and its relation to photochromic systems is described briefly.