LINEAR AND NONLINEAR-OPTICAL PROPERTIES OF THE DIFFERENT LANGMUIR-BLODGETT PHASES OF CNH2N+1-Q3CNQ

(Z)-alpha-cyano-beta-(N-hexadecylquinolin-4-ylium)-4-styryldicyanomethanide, C16H33-Q3CNQ, has two Langmuir-Blodgett (LB) phases that differ in thickness, tilt angle and second-order susceptibility. For phase I, I=2.2 nm layer(-1), phi=8 degrees and chi(zzz)((2))=180 pm V-1 at 1.064 mu m, whereas for phase II, I=1.6 nm layer(-1), phi=24 degrees and chi(zzz)((2))=100 pm V-1. The susceptibility of phase I is the highest so far reported for an LB multilayer; the structure is non-centrosymmetric (Z-type) and, as predicted by theory, the second-harmonic intensity varies as I-2 omega(N)=I-2 omega(1)N-2 as N increases from 1 to 200 layers. In contrast, C10H21-Q3CNQ has a low susceptibility (chi(zzz)((2))=6 pm V-1) and neutron reflectivity studies have indicated an antiparallel alignment of chromophores at the air/water interface.