Abstract
We have found that the assembly of J-aggregates in a merocyanine monolayer Langmuir-Blodgett (LB) film has noncentrosymmetric structure by surface second-harmonic generation (SHG). The chromophores align along an average direction, so that the symmetry is C2v. The pure merocyanine monolayer has a large second-order nonlinear susceptibility χzzz=1.3×10-7 esu, because of the noncentrosymmetric domain of J-aggregates. The dissociation of the aggregates occurs by heating, resulting in negligible SHG activity due to random orientation of the chromophore on the surface plane. We also confirmed the long-range anisotropic orientation of the chromophore over several millimeters.
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