Electronic structure and nonlinear optical properties of push–pull conjugated molecules

We present a review of ab initio calculations we recently performed on organic molecules presenting promising quadratic nonlinear optical properties. These molecules constitute so‐called push–pull conjugated compounds in which a conjugated segment is capped at one end by an acceptor group and at the other end by a donor group. We foucs on three series of systems: (i) p ‐amino‐ p ′‐nitrodiphenylacetylenes for which “unusual” distorsion patterns have been recently reported; (ii) benzodithiapolyenals, which present among the largest second‐order polarizabilities ever measured; and (iii) 2‐methylene‐2 H ‐pyrrole derivatives. Our results are found to provide a detailed understanding of the avilable experimental data.