Predicting nonlinear optical properties in push–pull molecules based on methyl pyridinium donor and 3-cyano-5,5-dimethyl-2(5H)-furanylidene-propanedinitrile acceptor units using vibrational spectroscopy and density functional theory

The experimental Raman, electronic absorption and hyperpolarisability (β0) data are compared to the calculated parameters for three potential nonlinear optical materials based on methyl pyridinium donor and 3-cyano-5,5-dimethyl-2(5H)-furanylidene-propanedinitrile acceptor units linked by a π-chain of 3, 5 and 7 carbon atoms. Using a B3LYP functional with the 6-31G(d) basis set we obtain predictions of the β0 values within 20% of those observed in experiment. The inclusion of solvent in the calculations does not improve the prediction – indeed it becomes worse. This poorer performance is also reflected in the poorer correlation between calculated and experimental Raman spectra and electronic absorption spectra.