Second‐order Nonlinear Optical Properties of a Series of Azulene Derivatives

The first hyperpolarizabilities of a series of novel azulenic‐barbituric acid chromophores have been studied by using 12 excitation wavelengths, ranging from 900 to 1907 nm. The dispersion relation of the first hyperpolarizabilities of chromophors holds the same tendency as the experimental results. In addition. the static first hyperpolarizability β 0 of molecules was calculated by means of the Sum‐Over‐States (SOS) expression and the two‐level formula respectively. The results show that these molecules possess large static fast hyperpolarizabilities and the β 0 value increases as the donor or acceptor strength enhances; the distorted degree of molecules has also an important influence on the β 0 value.