Optical properties of cross-conjugated isopolydiacetylene oligomers as measured by ultraviolet-visible spectroscopy and the optical Kerr effect

A novel series of isopolydiacetylene oligomers have been characterized on the basis of their electronic absorption, emission and nonlinear optical properties. The ultraviolet-visible spectra indicate only a small shift to lower energy as a function of increasing oligomer length. To evaluate the third-order nonlinear susceptibilities, chi((3)), and second hyperpolarizabilities, gamma, of these oligomeric samples a new Kerr gate technique, differential optical Kerr effect detection, has been employed. A linear relationship between gamma and the number of repeat units is found, suggesting that the fixed-length linearly conjugated segments dominate the electronic polarizability. The largest nonlinearity was observed in the heptamer sample, displaying a second hyperpolarizability relative to the tetrahydrofuran solvent of gammaheptamer/gamma(T H F) = 181 +/- 9.