Computational studies of the non-linear optical properties of some three-dimensional molecules: effect of π–σ–π through bond interaction on the first hyperpolarizability

First static and dynamic hyperpolarizabilities (β0/β1.17) are calculated by means of semi-empirical molecular orbital methods for a series of donor/acceptor three-dimensional (3D) organic molecules containing π-electron donors/acceptors attached to a central aromatic ring in 1,3- and 5-positions through a σ-bond while the corresponding acceptors/donors are attached directly to the 2,4- and 6-positions. The π-orbitals of the donor/acceptor interact through the σ-skeleton with the central ring (π–σ–π through bond coupling) giving rise to intramolecular charge transfer in the excited states. Due to the 3D structure of the molecules both the dipolar and the octopolar components of β are non-zero. This coupled with fairly large off diagonal components of β and an absorption maxima in the blue region suggest that this structural motif could have potential applications in the development of non-linear optical materials.