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

Octupolar molecules are of particular interest in the field of nonlinear op tics due to their potentially large two or three-dimensional quadratic nonl inearities. In order to design molecules combining enhanced first hyperpola rizabilities and excellent transparency, we have implemented an original st rategy based upon adequate functionalization of an orthogonalized biphenyl core. We have designed novel 3-dimensional all-organic octupoles of D-2d sy mmetry and investigated their optical nonlinearities by performing harmonic light scattering experiments in solution. By grafting four electron-donati ng and/or electron withdrawing substituents on the central biphenyl unit, l arge molecular nonlinearities (beta) have been achieved while maintaining f ull transparency in the visible range. Molecules displaying larger nonlinea rities and better transparency than pNA have been obtained. Molecular optim ization has been further pursued via tethering elongated conjugated spikes on the central biphenyl core and taking advantage of multidimensional charg e transfer leading to 3D-octupolar molecules displaying both larger nonline arity and broader transparency than DR1 (up to beta(xyz) = 145 x 10(-30) es u with lambda(max) = 400 nm). (C) 1999 Elsevier Science B.V. All rights res erved.