Measurement of quadratic hyperpolarizabilities of unsymmetrical donor-acceptor bi- and polyaryls: effect of size and torsion angle of aryl units

The linear and quadratic nonlinear optical properties of donor-acceptor polyphenyls and naphthyl derivatives are in investigated. The behaviour of the static first-order hyperpolarizability β(O) as a function of the number n of phenyl units separating an acceptor group (cyano) and a donor group (methylthio) is studied for n=1, 2, 3, and compared to that of similar polyphenyls bearing other donor substitutents (N,N-dimethylamino, methoxy). β(O) is also measured for unsymmetrical donor-acceptor biaryls containing at least one napthyl unit. A clear influence of the twist angle between the two units on the quadratic nonlinear response of the molecule is evidenced, allowing for fine control of the transparency/nonlinear efficiency trade-off.