Calculations of optical properties of the tetraphenyl-X family of isomorphous crystals (X = C, Si, Ge, Sn, Pb)

Abstract

As part of a program to determine how small structural changes become manifest in the optical properties of crystals we used classical dipole–dipole interaction calculations to estimate the linear birefringence and optical rotatory power of the crystals Ph₄X where X = C, Si, Ge, Sn, and Pb. Field induced effects including second harmonic generation, the electro-optic response and electrogyration were calculated using the dipole electron shifting model (DES) model. The calculated induced effects are larger than those in standard materials such as KH₂PO₄. All of the properties tend to increase in magnitude with increasing polarizability except for optical rotation, which is largest for Ph₄C. We propose an interpretation for the unusual behaviour of the optical rotation in terms of competing helical circuits of closely bonded atoms.