Optical second harmonic generation in Langmuir–Blodgett films of n-docosyl-2-methyl-4-nitroaniline

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Abstract
The preparation of Langmuir–Blodgett (LB) films of n‐docosyl‐2‐methyl‐4‐nitroaniline (DCMNA) is reported. LB multilayers of DCMNA are highly anisotropic showing a strong absorption for light polarized parallel to the dipping direction. Furthermore, optical second harmonic generation was observed from LB multilayers of DCMNA. The SH signal was always polarized parallel to the dipping direction; and maximum SH intensity was obtained when the direction of the fundamental wave was also polarized parallel to this direction. The SH intensity increased quadratically with the number of LB layers up to 50 layers. Preliminary x‐ray diffraction studies indicate a Y‐type arrangement for the molecules with a bilayer spacing of 3.77 nm and a strong tilt angle of 34° for the alkyl chains with respect to the substrate plane.