Towards highly efficient nonlinear optical chromophores: molecular engineering of octupolar molecules

Octupolar molecules are of particular interest in the field of nonlinear optics due to their potentially large two or three-dimensional quadratic nonlinearities. In order to design molecules combining enhanced first hyperpolarizabilities and excellent transparency, we have implemented an original strategy based upon adequate functionalization of an orthogonalized biphenyl core. We have designed novel 3-dimensional all-organic octupoles of D-2d symmetry and investigated their optical nonlinearities by performing harmonic light scattering experiments in solution. By grafting four electron-donating and/or electron withdrawing substituents on the central biphenyl unit, large molecular nonlinearities (beta) have been achieved while maintaining full transparency in the visible range. Molecules displaying larger nonlinearities and better transparency than pNA have been obtained. Molecular optimization has been further pursued via tethering elongated conjugated spikes on the central biphenyl core and taking advantage of multidimensional charge transfer leading to 3D-octupolar molecules displaying both larger nonlinearity and broader transparency than DR1 (up to beta(xyz) = 145 x 10(-30) esu with lambda(max) = 400 nm). (C) 1999 Elsevier Science B.V. All rights reserved.