Space Size-Dependent Transformation of Tetraphenylethylene Carboxylate Aggregates by Ice Confinement

Abstract

Tetraphenylethylene carboxylate (TPEC) aggregates are transformed by ice confinement, which is controlled by the initial concentration of sucrose employed as a cryoprotectant and temperature. The freezing of aqueous sucrose leads to the formation of micro- or nanoliquid phase confined in ice. Aggregation-induced emission (AIE) of tetraphenylethylene carboxylate (TPEC) in the ice-confined space is explored using fluorescence spectroscopy and lifetime measurements. The characteristics of AIE in the ice-confined space strongly depend on the initial sucrose concentration and temperature, which determine the size of the liquid phase. The AIE of TPEC in the ice-confined space can be classified into three regimes in terms of spectroscopic features. Loosely packed J aggregates of TPEC are formed in the microliquid phase (>2 μm). The fluorescence intensity increases, and the wavelength is hypsochromically shifted with a decrease in the size of the space, indicating that the molecular arrangement in the aggregate depends on the space size. The fluorescence lifetimes indicate polydisperse, loosely packed aggregation. No further change in aggregate structure is observed once the liquid phase size is decreased to ∼2 μm, and a spectroscopically identical structure is maintained upon further reduction of the space size to ∼0.5 μm. The molecular arrangement in the aggregate is independent of the space size in this regime. However, when the size of the space becomes smaller than ∼0.5 μm, the aggregate structure again starts to change into a more tightly packed aggregate and a hypsochromic shift of the fluorescence wavelength occurs again. The fluorescence lifetime indicates monodispersed aggregation in this submicrospace.

Fluorescence “Turn-On” Enzyme-Responsive Supra-Amphiphile Fabricated by Host–Guest Recognition between γ-Cyclodextrin and a Tetraphenylethylene-Sodium Glycyrrhetinate Conjugate

“…However, α-CD and β-CD had no significant effect on the absorption of TPE-SGA (Figure b). It is known that the self-assembly of TPE derivative tends to afford fluorescent J-aggregates concomitant with a bathochromic shift. − In contrast, the disassembly of J-aggregates would lead to a hypsochromic shift of absorption. Therefore, the hypsochromic effect induced by the addition of γ-CD indicates the deaggregation of TPE-SGA.…”

In situ Visualization of Ferrous Ions Dissolved from Pure Iron Wire into Thin Frozen Aqueous Solution Films by Combination of Microscopy and Image Processing

“…(4) In FCSs, some unusual chemical phenomena including the acceleration of chemical reactions under subzero conditions and dissolution of chemical species insoluble in water have been reported. (5)(6)(7)(8)(9)(10)(11)(12) These effects are attributed to the unique physicochemical properties of FCSs, induced by the microscale phase transitions at ice/solution interfaces. (13)(14)(15) The reductive reactions of metal oxides and their dissolution have also been reported to be accelerated in FCSs.…”

Freezing Enhances Leaching of Ferrous Ions but Hinders Reductive Dissolution of Ferric Ions from Iron Oxides

“…These phenomena could not be interpreted solely by freeze concentration. We have suggested that the interface between ice and a solution phase (freeze concentrated solution, FCS) should play an essential role because most of the freeze-specific phenomena become more marked as the interface/volume ratio increases. − In the present work, we studied the redox behaviors of iron oxides using cyclic voltammetry (CV) in frozen solutions and found some interesting freeze-specific phenomena; hereinafter, we call this method “freeze CV” to distinguish it from usual CV in solutions. , Freeze CV allows us to study phenomena that occur at the electrode interface with the FCS. A use of an electrode, in which iron oxides are incorporated, is expected to provide information on the redox processes of the iron oxides at the FCS interface and to allow us to discuss the freeze effects on their behaviors.…”

“…We have reported some interesting freeze-specific phenomena, including enhanced dissolution of organic compounds, − enhanced complexation of crown ethers, acceleration of pseudo-first-order reaction, and so forth. These phenomena could not be interpreted solely by freeze concentration.…”