Effect of medium polarity on the second-order polarizability of an octupolar chromophore: An ab initio reaction field study of triaminotrinitrobenzene

The Self-Consistent Reaction Field theory (extended to include an ellipsoidal cavity for the solute and a multipolar expansion of the field) is used to investigate the influence of medium polarity on the second-order nonlinear optical response of the prototypical octupolar compound 1,3,5-triamino-2,4,6-trinitrobenzene, TATB. Despite the absence of any dipole moment in TATB, the effect of medium polarity is found to be significant; for instance, the β_zzz tensor component of TATB is calculated to be twice as large in dichloromethane (electric permittivity ε = 9.1) as in the gas phase (ε = 1). This enhancement factor is similar to, though somewhat smaller than the one calculated for the dipolar counterpart of TATB, i.e. p-nitroaniline.