Kinetic Analysis by Laser Flash Photolysis of Porphyrin Molecules’ Orientation Change at the Surface of Silicate Nanosheet

Abstract

In a mixed solvent of water and dimethylformamide (DMF), porphyrin molecules have two types of orientation, tilted and parallel, toward a surface of silicate nanosheet. In the solvent, tilted species have lower energy. The T n ← T 1 absorption of porphyrin molecules adsorbed at the surface of the nanosheet in the mixed solvent was observed at five different temperatures. The decay curve was analyzed with an equation for transient absorption difference, describing the behavior of parallel and tilted adsorbed species in the ground state and excited state to determine the rate constants for the orientation change and the radiationless deactivation. The rate constants of the orientation change increased with the temperature. The activation energy and energy gap between parallel and tilted species were estimated by analyzing the temperature dependence of the rate constants. The energy gap obtained in this kinetic study was consistent with our thermodynamically obtained value previously reported.

Kinetics of Interlayer Expansion of a Layered Silicate Driven by Caffeine Intercalation in the Water Phase Using Transmission X-ray Diffraction

“…1.0 nm) crystalline silicate layers and hydrated exchangeable cations. Cation-exchange reactions of the interlayer cations with a small-size organoammonium (e.g., tetramethylammonium) create nanospaces in the interlayer space, , which can accommodate nonionic organic molecules by size exclusion effect in the interlayer space without interlayer expansion. ,,,,− On the other hand, the expansion may occur upon the intercalation of nonionic organic compounds, when the organic cations adopt a planar geometry. ,− In the water phase, such structural flexibility is potentially adaptable for the uptake of a target molecule; intercalation of water molecules through hydrogen bonding expands the interlayer spaces and thus possibly creates nanostructures to accommodate a target. Selective removal of caffeine (Scheme a) in tea has attracted attention especially in the beverage industry because of diminishing their negative effects on health, such as sleep disorder, elevation of blood pressure, and risk of fetal growth disorder .…”

Diphenyldihydropentalenediones: Potential Singlet Fission Materials with High Triplet Energy Levels

“…The photophysical properties of crystals of the PDs were also determined. The absorption spectra of PD-H, PD-OCH3, and PD-CF3 crystals, obtained using a waveguide technique, [56][57][58] contain maxima at 352, 422, and 355 nm, respectively, that are similar to those of corresponding CH2Cl2 solutions. The FL spectra of PD-H, PD-OCH3, and PD-CF3 crystals contain maximum at 487, 531, and 467 nm, respectively, which are also close to those of CH2Cl2 solutions.…”

Diphenyldihydropentalenediones: Potential Singlet Fission Materials with High Triplet Energy Levels

“…The photophysical properties of crystals of the PDs were also determined. The absorption spectra of PD-H, PD-OCH3, and PD-CF3 crystals, obtained using a waveguide technique, [62][63][64] contain maxima at 352, 422, and 355 nm, respectively, that are similar to those of corresponding CH2Cl2 solutions. The FL spectra of PD-H, PD-OCH3, and PD-CF3 crystals contain maximum at 487, 531, and 467 nm, respectively, which are also close to those of CH2Cl2 solutions.…”