Engineering Second-Order Nonlinear Optical Activity by Means of a Noncentrosymmetric Distortion of the [Te−N]₂ Supramolecular Synthon

Moderate steric repulsion within the supramolecular ribbon chains assembled by 1,2,5-telluradiazole derivatives causes a distortion of the [Te−N]₂ supramolecular synthon which removes the inversion center from the four-membered virtual ring. This geometrical feature can propagate through the lattice, creating a noncentrosymmetric crystal with second-order nonlinear optical (NLO) properties. This principle was demonstrated in the cases of 3,4-dicyano-1,2,5-telluradiazole and 5,6-dichlorobenzo-2,1,3-telluradiazole. The second harmonic generation efficiency of these materials, however, is modest because the molecular dipole moments have a nearly antiparallel arrangement in the ribbons. The structure of 5-benzoylbenzo-2,1,3-telluradiazole demonstrates that it is indeed possible to extend this strategy to generate acentric crystals of benzo-2,1,3-telluradiazoles featuring pendant groups (including NLO chromophores) and in this way design more efficient NLO materials.