Langmuir-Blodgett deposition and non-linear optical properties of a two-legged dye

The two-legged dye, E-N-hexadecyl-2-[2-(4-octadecylaminophenyl)ethenyl]benzothiazolium iodide, adopts a 'stretched' rather than a 'U-shaped' configuration at the air/water interface and aligns with one of its hydrophobic alkyl groups adjacent to the subphase. Its Langmuir-Blodgett (LB) films are noncentrosymmetric but lack long-range order, with the chromophores having tilt angles relative to the substrate normal of 35+/-2 degrees in the monolayer and 50+/-5 degrees in a 300-layer film. The second-order susceptibility of the monolayer its thickness and the real and imaginary components of the dielectric permittivity are chi(zzz)((2)) = 80 pm V-1 at 1.064 mu m and l = 4.89 nm, epsilon(r) = 3.21 and epsilon(i) = 1.53 at 532 nm (lambda(2 omega)). The second-harmonic intensity increases subquadratically with the number of LB layers, saturating after ca. 100 layers, the susceptibility decreasing with increasing film thickness. (C) 1997 Elsevier Science Ltd. All rights reserved.