Optical properties of a quinoid molecule

We report on linear and third order nonlinear optical properties of the quinoid molecule 5,5′-bis(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadiene-1-ylidene)-5,5′-dihydro-2, 2′-bithiophene.Variable angle spectroscopic ellipsometry has been used to determine the dispersion of the dielectric in a spectral range from the near infrared to the near ultraviolet. We have measured a high value of the index of refraction in the transparency region (i.e., n=1.886 at λ=1.5 μm), indicating the high polarisability of the molecule under study. The nonlinear optical properties have been measured by third harmonic generation in the near infrared spectral range. At λ=1.5 μm the nonlinear coefficient of the molecule has been estimated to be 4.2 × 10−19 m2/V2 (3.0 × 10−11 esu).