Spectroscopy of MPS(3):DAMS(+) composite materials

Composite materials are comprised of two separate components that are brought together to form a new material that exhibits unique properties not found in the individual components. The composite material studied in this work is a guest dye cation, (4-[4-(dimethylamino)-α-styrl]-1-methylpyridinium) or DAMS+, intercalated into an inorganic host lattice (MPS ₃, where M = Cd2+ or Mn2+). MPS₃ :DAMS+ exhibits high-efficiency second-harmonic generation (SHG), which is only observed when a material lacks a center of symmetry. There must be an organization of dye molecules upon intercalation to induce the noncentrosymmetry necessary for SHG. The formation of dye aggregates will be studied as a possible noncentrosymmetric arrangement.; The intercalated materials (MPS₃:DAMS+) exhibited spectral features of J-aggregates. These features included a sharp aggregate absorption and emission band, known as the J-band. There was a small Stokes shift (250 cm−1) between aggregate absorption and emission bands, and a red-shift between the J-band and isolated dye absorption band (3,700 cm−1). The low-energy tail of the emission J-band was theoretically modeled using the Urbach-Martienssen equation, while the high-energy states were fit to a Gaussian to determine aggregate disorder. Disorder was also modeled using a Monte-Carlo lineshape analysis program. From these theoretical models, the aggregate was found to be two-dimensional and weakly coupled. A variety of sample types were studied including intercalated powders and single crystals using absorbance, reflectance and emission spectroscopy. Reflectance spectra were directly compared with absorbance spectra using the Kramers-Kronig Transformation2 to determine that the surface aggregates and the interior aggregates were structurally similar.; A new imaging microspectrophotometer was developed to investigate the topology of the composite materials. Kinetics of the intercalation front were studied and a layer-by-layer intercalation mechanism was developed. Surface studies using other materials indicated the polyanion nature of MPS₃ :DAMS+ was essential for aggregation. Infrared microspectroscopy was used to determine the orientation of dye molecules on the surface of the large composite crystals. The DAMS+ in MPS ₃:DAMS+ was shown to form two-dimensional brickwork aggregates with the molecules aligned “edge-on” on the surface and interior of the host lattice.