Large enhancement of electronic first hyperpolarizability in Donor1–π–Donor2 chromophores with charge defects

New strategy in the design of non-linear optical molecular switches has been studied using correlated ab initio methods. The employment of Donor1–π–Donor2 chromophores in contrast to the classical Donor–π–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 Donor1–π–Donor2 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.