New strategy in the design of non-linear optical molecular switches has been studied using correlated ab initio methods. The employment of Donor(1)-pi-Donor(2) chromophores in contrast to the classical Donor-pi-Acceptor molecules shows a more efficient modulation of the first hyperpolarizability upon oxidation. This is due to the large enhancement of the first hyperpolarizability obtained in Donor(1)-pi-Donor(2) chromophores with charge defects, which is about 27 times higher than that of a standard DA chromophore of the same size. This enhancement is explained using electron density derivatives, showing that the introduction of charge defects converts the powerful electron donor group into a strong electron acceptor group. (C) 2004 Elsevier B.V. All rights reserved.