Non-linear Optical Constants from Molecular Hyperpolarisabilities: II. Application to Donor- Acceptor molecules

The molecular polarisability and hyperpolarisability tensors of a group of donoracceptor polyene molecules are calculated using the time dependent Hartree-Fock code implemented in the MOPAC quantum chemistry program. The results agree with other theoretical and experimental calculations. The values obtained are then used to investigate mutual polarisation of collections of such molecules, e.g. as chromophore side chains in an optical polymer, using the electrostatic quadratic tensor model developed in the previous article. The performance of the model is first confirmed by comparison with MOPAC calculations of composite molecules containing a pair of chromophores, and then applied to linear polymer chains as well as lattices in 2 and 3 dimensions. An optimal chromophore packing density is determined to maximise the macroscopic susceptibilities of polymer materials of the type studied. This is lower than the density allowed by the structure of the polymer, because of the mutual depolarisation of chromophores at high packing densities. Current address: Applied Computing, Mathematics and Statistics Group, Lincoln University, Canterbury, NEW ZEALAND