Theoretical study on the nonlinear optical properties of phenylenes and influencing factors

A systematic investigation of the hyperpolarisabilities of substituted p‐poly‐phenylenes is presented using different quantum mechanical approaches, including density functional theory and Møller–Plesset (MP2) methods. A medium‐sized basis set Hartree–Fock (HF) hyperpolarisability calculation based on either a density functional theory (DFT) or MP2 geometry gives reliable results at moderate computational costs when comparing with experimental data. A longer phenylene chain leads to a maximum in the per‐unit increase of the investigated property between 3 and 4 repeat units. Changing the underlying geometry from the minimum helix to a planar orientation leads to a significant increase in β, again dependent on the chain length. Terminal para‐substituents and their influence are studied and categorised. For push–pull groups, the substituent effects are mainly additive, allowing the design of functionalised phenylenes as molecular building blocks for nanofibres with tailored nonlinear optical (NLO) properties. Copyright © 2008 John Wiley & Sons, Ltd.