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Evanescent wave cavity ring-down absorption spectroscopy is applied to measure the thermodynamic properties of the surface adsorption for neutral trans-4-[4-(dibutylamino)styryl]-1-(3-sulfopropyl) pyridinium (DP) and charged trans-4-[4-(dibutylamino)styryl]-1-methylpyridinium iodide ([DMP.sup.+][I.sup.-]) at the silica/[CH.sub.3]CN interface, where the interfacial density is determined by measurement of absorbance. The bulk concentration dependence of the surface density may be characterized with a Langmuir isotherm model, which yields saturated surface density, equilibrium constant, and free energy of adsorption of (7.0 [+ or -] 0.3) x [10.sup.13] [cm.sup.-2], (1.3 [+ or -] 0.2) x [10.sup.4] [M.sup.-1], and -23.5 [+ or -] 0.4 kJ/mol for DP and (8.9 [+ or -] 0.3) x [10.sup.12] [cm.sup.-2], (2.6 [+ or -] 0.7) x [10.sup.4] [M.sup.-1], and -25.2 [+ or -] 0.6 kJ/mol for [DMP.sup.+][I.sup.-], respectively. The surface density of the isolated silanol groups may then be estimated in terms of the molecular probe results. The absorption contribution from the bulk solution is a factor of ~[10.sup.-][10.sup.2] smaller than the total absorbance measured such that subtraction of the bulk contribution leads to negligible change of the thermodynamic properties. The DP is adsorbed to the SiOH sites by forming hydrogen bonds, while the [DMP.sup.+] cation is bound to the Si[O.sup.-] sites by electrostatic attraction. Surface forces are also probed by addition of triethylamine (TEA), which is competitive with DP for the silanol sites. When the TEA concentration is increased, the DP surface density is found to decrease, whereas the [DMP.sup.+] surface density increases. The ob- tained thermodynamic properties are generally consistent with those measured by second harmonic generation spectroscopy. However, when a tetramethylammonium ([([CH.sub.3]).sub.4][N.sup.+][Cl.sup.-]) salt is added, the [DMP.sup.+] cation behaves differently between these two methods. Formation of an electrical double layer may account for the difference.

Molecular dynamics simulations are used for calculating the optical Kerr effect (OKE) spectra of 1-methoxyethylpyridinium dicyanoamide, a room-temperature ionic liquid (IL). The studies have shown that the theoretical methodology has a vital impact on the speed of molecular dynamics simulations of polarizable systems.

The extraordinary stability of the photoinduced red form of a cationic spiropyran is used for obtaining in situ X-ray diffraction evidence of its molecular structure. The density functional theory calculations have shown that the stabilization of the red form of the cationic relative to the neutral spiropyran is thermodynamically controlled, through compensation of the charge within the zwitterion by the methylpyridinium group.

The self-sorting of the coordination-driven self-assembly of two-dimensional (2-D) polygons and three-dimensional (3-D) cages, which is carried out by mixing different sized ditopic bispyridyl or tritopic trispyridyl donors with a molecular clip and 60 degree acceptor is reported. In all cases, the self-sorting process is directed by the size of the donor building blocks and a dynamic, thermodynamically driven self-correction process resulting in the formation of discrete products from complex mixtures.

The thermophysical studies of two isomeric room-temperature ionic liquids (RTILs), n-butyl-3-methyl-pyridinium tetrafluoroborate and n-butyl-4-methyl-pyridinium tetrafluoroborate are presented. The results from the studies helped to obtain the coefficients of thermal expansion, molar refractions, and dynamic viscosities and calculate the entropies and enthalpies of surface formation per unit surface area.

The calculations of equilibrium thermodynamic and structural properties concerning the cations alkylimidazolium, tetra-alkylphosphonium, and N-alkylpyridinium, and anions chloride, bromide, and dicyanamide is reported. The results show that the rotation of the methyl group around the NAP-C1 bond in N-methylimidazolium is almost free, whereas the C1-C2 bond in longer alkyl chains adopts an orientation perpendicular to the aromatic ring.

Bis-axially ligated iron(III) complexes of five tetra-(2,6-disubstituted phenyl)porphyrines, with 1-MeIm, 2-MeHIm, and nine substituted pyridines with pKa(PyH(super +))=9.7 to 1.1 were investigated. The high basicity pyridine complexes exhibited Curie behavior for their pyrrole-H resonance, while the lower basicity pyridine complexes showed significant deviations from simple Curie behavior that are consistent with the existence of a mixed configuration ground state and a thermally accessible excited state.