We report optical second harmonic generation studies of the organic dye molecule rhodamine 6G spin cast on fused silica surfaces. The concentration dependence of the second harmonic response demonstrates oscillatory behavior with a period corresponding to the concentration required for monolayer surface coverage. This behavior reflects the formation of ordered molecular adlayers which persist for approximately five periods. Polarized SHG studies confirm orientational anisotropy of the dye molecules and allow the orientation within adjacent layers to be determined. Optical absorbance measurements of the films indicate the onset of rhodamine 6G aggregate formation at surface coverages of approximately one monolayer. However, the onset of dimer or aggregate fluorescence is observed to occur only at much higher surface coverages, consistent with the loss of orientational order within the adlayers. Our results indicate strong adsorbate-substrate interaction which gives rise to orientational anisotropy within the first molecular layer. Well-defined order within subsequent layers is determined by interlayer adsorbate-adsorbate aggregation and decays on a length scale of several molecular diameters. These results provide a direct measure of the extent of interfacial ordering at the solid/air interface.

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Using two types of triol ligands, several novel asymmetrically triol-functionalized Anderson organic hybrids have been efficiently synthesized in high purity and good yields via a convenient two-step esterification reaction. These organic-inorganic hybrids are chiral and can be spontaneously resolved with suitable solvents. Their molecular and crystal structures have been confirmed by single-crystal X-ray diffraction studies. Stable solid-state chirality of the corresponding enantiopure crystals has also been confirmed definitively by CD spectra. Interestingly, these organic-inorganic hybrids possess a layer-by-layer structure, forming solvent-accessible nanoscale chiral channels via a 1D infinite helical chain substructure. TGA measurements indicated that the species of the central heteroatoms significantly effects the stability of these compounds.

We conducted in situ angle dispersive high pressure x-ray diffraction experiments on Sr3Ir2O7 up to 23.1 GPa at 25 K with neon as the pressure transmitting medium. Pressure induces a highly anisotropic compressional behavior seen where the tetragonal plane is compressed much faster than the perpendicular direction. By analyzing different aspects of the diffraction data, a second-order structural transition is observed at approximately 14 GPa, which is accompanied by the insulating state to nearly metallic state at 13.2 GPa observed previously (Li et al 2013 Phys. Rev. B 87 235127). Our results highlight the coupling between electronic state and lattice structure in Sr3Ir2O7 under pressure.