ABSTRACT
Langmuir-Blodgett (LB) films of E-4-[(N-octadecyl-6,7,8-trihydro-5-isoquinolylidene)methyl]-N,N-diethylaniline octadecylsulfate show improved second-harmonic generation (SHG) when the dye is co-deposited in a 1:1 ratio with octadecanoic acid. In addition, when interleaved with poly(£- butyl methacrylate), the molecules adopt a non-centrosymmetric arrange ment and the second-harmonic intensity increases as 1 ^ ~ I^N2 where N is the number of active layers. The films are transparent at the fundamental wavelength (1.064 |im) and have a very slight absorbance of 5 x 10^ bilayer-1 at 532 nm. The normalized intensity, /(^ /N 2, is ca. 300% of the resonantly enhanced signal from monolayer films of the extensively studied hemicyanine dye, E-N-docosyl-4-[2-(4-dimethylaminophenyl)ethenyl]pyridinium bromide, this improved nonlinear optical behaviour being attributed, in part, to an optimised packing arrangement and, in part, to the close prox imity of the charge-transfer band. The second-order susceptibility, repeat distance and refractive indices of the interleaved film (104 bilayers) are
= 67pmV-1 and xfjx = 19pmV-1 at 1.064|im, /=4.08nmbilayer-1, 7^=1.495 and n2tJJ= 1.581 respectively.
