USE OF THIAZOLE RINGS TO ENHANCE MOLECULAR 2ND-ORDER NONLINEAR OPTICAL SUSCEPTIBILITIES

It is shown that the appropriate replacement of benzene-ring structures by thiazole rings in polar donor-acceptor molecules will result in an increase of the microscopic scalar second-order nonlinear optical quantity, μ0β, of up to a factor of ≈3. Electric field induced second harmonic generation (EFISH) results are presented for two species of this type and compared to the corresponding benzenoid structures. In general, the results show the increases in μ0β to be largely due to dispersion, with smaller effects seen in dipole and transition moments. There is a significant narrowing of the transition band from 2Γ ≈ 3530 cm−1 to 2T ≈ 2110 cm−1 upon replacement of benzene by thiazole, thus keeping the effects of damping relatively constant and permitting ready application of these dyes for electrooptic device applications in the near IR (≳1300 nm). Scalar μ0β as large as ≈ 5300 D cm5 esu−1 (λ2ω = 789.5 nm; λmax = 645 nm; Γ = 1057 cm−1, the half-width at half-maximum) are observed for a (dicyanovinyl)thiazole azo dye. © 1990, American Chemical Society. All rights reserved.