Molecular quadratic hyperpolarizability (beta(c)) of substituted polychlorinated triphenylmethyl radicals, 1-8, has been determined by using the harmonic light scattering (HLS) technique. Results showed that this opens-shell family known to possess a good chemical stability also exhibited a very large SONLO response. The presence of a permanent dipole moment in the ground state for some of these octupolar compounds makes them attractive candidates for further orientation by the poling technique. Data of compounds 1-8 have been discussed on the basis of a model describing the evolution of the beta(c), response for D-3h and C-2v Symmetry groups. (C) 2002 Elsevier Science B.V. All rights reserved.