Structure and Lateral Interaction in Mixed Monolayers of Dioctadecyldimethylammonium Chloride (DOAC) and Stearyl Alcohol

π–<i>A</i> isotherms, atomic force microscopy (AFM), and sum frequency generation (SFG) vibrational spectroscopy are employed to investigate the molecular structure and lateral interactions in mixed monolayers of dioctadecyldimethylammonium chloride (DOAC) and stearyl alcohol (SA) at air/water and air/solid interfaces. To avoid possible interference between the two molecules in the SFG spectroscopic measurements, perprotonated DOAC and perdeuterated SA (dSA) were used. The thermodynamic analyses for the π–<i>A</i> isotherms show that DOAC is miscible with dSA. SFG observations reveal that DOAC molecules become conformationally ordered as dSA molecules are introduced into the monolayer. AFM observations demonstrate coexistence of DOAC-rich and dSA-rich domains in the mixed monolayer with ratios different from their initial composition in the subphase. The present study suggests that DOAC molecules in the mixed monolayer are condensed by mixing with dSA in which the repulsive interactions between positively charged head groups of the DOAC molecules are largely reduced along with an increase of van der Waals interactions with dSA

Characterizing the Photoinduced Switching Process of a Nitrospiropyran Self-Assembled Monolayer Using In Situ Sum Frequency Generation Spectroscopy

Sum frequency generation (SFG) vibrational spectroscopy is employed to investigate the reversible, photoinduced spiro→merocyanine isomerization of a self-assembled monolayer, the result of attachment of nitrospiropyran to a gold surface using a dithiolane anchoring group. The attachment of these molecular “alligator clips” to spiropyran molecules provide an easily accessible method to self-assemble a robust monolayer of spiropyran on a gold surface, which allows photoswitching of the spiropyran units. Probing the symmetric and antisymmetric stretching modes of the nitro group allows the determination of the structural orientation of the charged moiety with respect to the surface normal as well as the isomerization rates under photoinduced switching conditions. The photoisomerization of the spiropyran SAM on the gold surface is much faster than the rates of switching spiropyrans in a solid crystalline form, and the rate of thermal relaxation of the opened to closed form in this study is found to be on the same time scale as the relaxation of spiropyran when present in solutions with polar solvents

Deuteration of Perylene Enhances Photochemical Upconversion Efficiency

Photochemical upconversion via triplet–triplet annihilation is a promising technology for improving the efficiency of photovoltaic devices. Previous studies have shown that the efficiency of upconversion depends largely on two rate constants intrinsic to the emitting species. Here, we report that one of these rate constants can be altered by deuteration, leading to enhanced upconversion efficiency. For perylene, deuteration decreases the first order decay rate constant by 16 ± 9% at 298 K, which increases the linear upconversion response by 45 ± 21% in the low excitation regime

Deuteration of Perylene Enhances Photochemical Upconversion Efficiency

Photochemical upconversion via triplet–triplet annihilation is a promising technology for improving the efficiency of photovoltaic devices. Previous studies have shown that the efficiency of upconversion depends largely on two rate constants intrinsic to the emitting species. Here, we report that one of these rate constants can be altered by deuteration, leading to enhanced upconversion efficiency. For perylene, deuteration decreases the first order decay rate constant by 16 ± 9% at 298 K, which increases the linear upconversion response by 45 ± 21% in the low excitation regime

Hydrogen Storage in the Expanded Pore Metal–Organic Frameworks M₂(dobpdc) (M = Mg, Mn, Fe, Co, Ni, Zn)

The hydrogen storage properties of a new family of isostructural metal–organic frameworks are reported. The frameworks M₂(dobpdc) (M = Mg, Mn, Fe, Co, Ni, Zn; dobpdc^4– = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate) are analogous to the widely studied M₂(dobdc) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn; dobdc^4– = 2,5-dioxido-1,4-benzenedicarboxylate) family of materials, featuring the same weak-field oxo-based ligand environment for the M²⁺ metal centers, but with a larger pore volume resulting from the extended length of the dobpdc^4– linker. Hydrogen gas adsorption isotherms measured at 77 and 87 K indicate strong H₂ binding at low pressures, corresponding to the adsorption of one molecule per M²⁺ site. Isosteric heats of adsorption indicate adsorption enthalpies ranging from −8.8 to −12.0 kJ/mol, with the trend Zn < Mn < Fe < Mg < Co < Ni. Room-temperature high-pressure adsorption isotherms indicate enhanced gravimetric uptakes compared to the M₂(dobdc) analogues, a result of the higher surface areas and pore volumes of the expanded frameworks. Indeed, powder neutron diffraction experiments performed on Fe₂(dobpdc) reveal two additional secondary H₂ adsorption sites not observed for the nonexpanded framework. While displaying higher gravimetric capacities than their nonexpanded counterparts, the larger pore volumes result in lower volumetric capacities. Upon comparison with other promising frameworks for hydrogen storage, it becomes evident that in order to design future materials for on-board hydrogen storage, care must be placed in achieving both a high surface area and a high volumetric density of exposed metal cation sites in order to maximize gravimetric and volumetric capacities simultaneously

Hydrogen Storage in the Expanded Pore Metal–Organic Frameworks M₂(dobpdc) (M = Mg, Mn, Fe, Co, Ni, Zn)

The hydrogen storage properties of a new family of isostructural metal–organic frameworks are reported. The frameworks M₂(dobpdc) (M = Mg, Mn, Fe, Co, Ni, Zn; dobpdc^4– = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate) are analogous to the widely studied M₂(dobdc) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn; dobdc^4– = 2,5-dioxido-1,4-benzenedicarboxylate) family of materials, featuring the same weak-field oxo-based ligand environment for the M²⁺ metal centers, but with a larger pore volume resulting from the extended length of the dobpdc^4– linker. Hydrogen gas adsorption isotherms measured at 77 and 87 K indicate strong H₂ binding at low pressures, corresponding to the adsorption of one molecule per M²⁺ site. Isosteric heats of adsorption indicate adsorption enthalpies ranging from −8.8 to −12.0 kJ/mol, with the trend Zn < Mn < Fe < Mg < Co < Ni. Room-temperature high-pressure adsorption isotherms indicate enhanced gravimetric uptakes compared to the M₂(dobdc) analogues, a result of the higher surface areas and pore volumes of the expanded frameworks. Indeed, powder neutron diffraction experiments performed on Fe₂(dobpdc) reveal two additional secondary H₂ adsorption sites not observed for the nonexpanded framework. While displaying higher gravimetric capacities than their nonexpanded counterparts, the larger pore volumes result in lower volumetric capacities. Upon comparison with other promising frameworks for hydrogen storage, it becomes evident that in order to design future materials for on-board hydrogen storage, care must be placed in achieving both a high surface area and a high volumetric density of exposed metal cation sites in order to maximize gravimetric and volumetric capacities simultaneously