From intercalation to aggregation: Nonlinear optical properties of stilbazolium chromophores-MPS(3) layered hybrid materials

A number of cationic chromophores derived from the stilbazolium skeleton have been synthesized and inserted into the transparent layered MPS(3) compounds (M = Mn, Cd, Zn). The NLO properties of the intercalates have been studied. Some of the materials are found to be active for second harmonic generation. UV-visible spectroscopy shows that some of the chromophores, once inserted, undergo strong intermolecular interactions and form J-type aggregates along the inorganic galleries, whereas others do not. Moreover, we have found that only those intercalates which contain aggregates are NLO active. The results allow us to understand, at least partially, why the centrosymmetrical MPS(3) host lattice can yield noncentrosymmetrical intercalates. The host lattice appears not so much to impose specific orientations upon the guest species as to favor chromophore aggregation.