Modulation of second harmonic generation properties of tolan and stilbene derivatives by monolayer assembling

Abstract

Push–pull tolan and stilbene derivatives, 4-docosylamino-4′-nitrotolan (ANT-22) and 4-octadecylamino-4′-nitrostilbene (ANS-18) could form rigid condensed monolayers on the water surface and ANT-22 was transferred as the alternating Y-type and the non-alternating X-type films by the vertical dipping (Langmuir–Blodgett) and the horizontal lifting methods, respectively. ANS-18 could be built up only in the X-type film by the horizontal lifting method. Both films exhibit considerable in-plane anisotropic second harmonic generation (SHG) signals, depending on the dipping direction and the direction of monolayer compression. In the latter case, the long axis of the NLO chromophore has a tendency to be oriented nearly perpendicular to the monolayer compression in the long and narrow trough. Then, the SHG intensity could be modulated by setting the plate position with the horizontal lifting method.