Self-assembled electrooptic superlattices. A theoretical study of multilayer formation and response using donor-acceptor, hydrogen-bond building blocks

The binding energies, electronic structures, and electrooptic responses of three donor-pi-system-acceptor (triazine-vinylbenzylidene-barbituric acid) chromophores that display substantial molecular hyperpolarizabilities and are capable of forming hydrogen-bonded, self-assembled multilayers are investigated using DFT (geometry) and semiempirical (electronic structure) methods. The geometries of the monomers, head-to-tail dimers, and head-to-tail trimers are computed, as well as the linear optical properties and hyperpolarizabilities. Although all three monomers are found to be planar, self-assembly removes monomer planarity and the resulting complexes are slightly twisted. It is found that the combination of dipole moment alignment and short distances between the monomers results in the hyperpolarizabilities of the trimers being substantially greater than three times those of the corresponding monomers, evidencing a synergistic effect that enhances the electrooptic response.