Amplification sensing manipulated by a sumanene-based supramolecular polymer as a dynamic allosteric effector.

The synthesis of signal-amplifying chemosensors induced by various triggers is a major challenge for multidisciplinary sciences. In this study, a signal-amplification system that was flexibly manipulated by a dynamic allosteric effector (trigger) was developed. Herein, the focus was on using the behavior of supramolecular polymerization to control the degree of polymerization by changing the concentration of a functional monomer. It was assumed that this control was facilitated by a gradually changing/dynamic allosteric effector. A curved-π buckybowl sumanene and a sumanene-based chemosensor (SC) were employed as the allosteric effector and the molecular binder, respectively. The hetero-supramolecular polymer, (SC·(sumanene)n), facilitated the manipulation of the degree of signal-amplification; this was accomplished by changing the sumanene monomer concentration, which resulted in up to a 62.5-fold amplification of a steroid. The current results and the concept proposed herein provide an alternate method to conventional chemosensors and signal-amplification systems.

Fluorophore-Probed Curdlan Polysaccharide Chemosensor: "Turn-On" Oligosaccharide Sensing in Aqueous Media.

The ability to sense saccharides in aqueous media has attracted much attention in multidisciplinary sciences because the detection of ultrahigh concentrations of sugar chains associated with serious diseases could lead to further health promotion. However, there are notable challenges. In this study, a rhodamine-modified Curdlan (Rhod-Cur) chemosensor was synthesized that exhibited distinctive fluorescence "turn-on" responses. Rhod-Cur exhibited simultaneous sensitive and selective sensing of clinically useful acarbose with a good limit of detection (5 µM) from among those of the saccharides examined. The (chir)optical properties of Rhod-Cur were elucidated using UV/vis, fluorescence, excitation, and circular dichroism spectroscopies; lifetime measurements and morphological studies using atomic force and confocal laser scanning microscopy and dynamic light scattering techniques revealed that the fluorescence "turn-on" behavior originates from globule-to-coaggregation conversion upon insertion of the oligosaccharides in the dynamic Cur backbone.

Pressure-Responsive Polymer Chemosensors for Hydrostatic-Pressure-Signal Detection: Poly-l-Lysine-Pyrene Conjugates.

Stimulus-responsive polymer materials are an attractive alternative to conventional supramolecular and polymer assemblies for applications in sensing, imaging, and drug-delivery systems. Herein, we synthesized a series of pyrene-labeled α- and ε-poly-l-lysine conjugates with varying degrees of substitution (DSs). Hydrostatic-pressure-UV/vis, fluorescence, and excitation spectroscopies and fluorescence lifetime measurements revealed ground-state conformers and excited-state ensembles emitting fluorescence with variable intensities. The polylysine-based chemosensors demonstrated diverse ratiometric responses to hydrostatic pressure through adjustments in polar solvents, DSs, and polymer backbones. Additionally, the fluorescence chemosensor exhibited a promising glum value of 3.2 × 10-3, indicating potential applications in chiral fluorescent materials. This study offers valuable insights into the development of smart hydrostatic-pressure-responsive polymer materials.

Sumanene-stacked supramolecular polymers. Dynamic, solvation-directed control.

In this study, we found that a pristine buckybowl, sumanene, can form solution-state supramolecular polymers. We also demonstrated that sumanene supramolecular polymers can be dynamically controlled by external stimuli, in which solvation plays a significant role. This study not only provides new guidelines for the rational design of supramolecular polymers, particularly for the use of buckybowls, but also presents interesting dynamic behaviors of supramolecular polymerization.

Control of intramolecular singlet fission in a pentacene dimer by hydrostatic pressure.

Singlet fission (SF), which produces two triplet excitons from a singlet exciton, has been identified as a novel nanointerface for efficient (photo)energy conversion. This study aims to control exciton formation in a pentacene dimer through intramolecular SF using hydrostatic pressure as an external stimulus. We reveal the hydrostatic-pressure-induced formation and dissociation processes of correlated triplet pairs (TT) in SF by means of pressure-dependent UV/vis and fluorescence spectrometry and fluorescence lifetime and nanosecond transient absorption measurements. The photophysical properties obtained under hydrostatic pressure suggested distinct acceleration of the SF dynamics by microenvironmental desolvation, the volumetric compaction of the TT intermediate based on solvent reorientation toward an individual triplet (T1), and pressure-induced shortening of T1 lifetimes. This study provides a new perspective on the control of SF by hydrostatic pressure as an attractive alternative to the conventional control strategy for SF-based materials.

Solution-State Hydrostatic Pressure Chemistry: Application to Molecular, Supramolecular, Polymer, and Biological Systems.

Pressure (P), as one of the most inherent state quantities, has become an academic subject of study and has attracted attention for a long time for the minute control of reaction equilibria and rates, not only in the gas phase, based on the gas state equation, but also in the solution state. In the latter case, the pressure applied to the solutions is classified as hydrostatic pressure, which is a type of isotropic mechanical force. For instance, deep-sea organisms are exposed to hydrostatic pressure environments of up to 100 MPa, implying that hydrostatic pressurization plays a role in homeostatic functions at physiological levels. The pressure control of such complicated biological behavior can be addressed by thermodynamics or kinetics. In fact, the spontaneity (ΔG) of a reaction that is governed by weak interactions (approximately 10 kcal/mol), such as electrostatic, van der Waals, hydrophobic, hydrogen bonding, and π-π stacking, is determined by the exquisite balance of enthalpy (ΔH) and entropy changes (ΔS), in accordance with the fundamental thermodynamic equation ΔG = ΔH - TΔS. The mutually correlated ΔH-ΔS relationship is known as the enthalpy-entropy compensation law, in which a more negative enthalpic change (more exothermic) causes further entropic loss based on a more negative entropy change. Namely, changing the temperature (T) as the state quantity, except for P, is highly likely to be equal to controlling the entropy term. The solution-state entropy term is relatively vague, mainly based on solvation, and thus unpredictable, even using high-cost quantum mechanical calculations because of the vast number of solvation molecules. Hence, such entropy control is not always feasible and must be demonstrated on a trial-and-error basis. Furthermore, the above-mentioned equation can be rearranged as ΔG = ΔF + PΔV, enabling us to control solution-state reactions by simply changing P as hydrostatic pressure based on the volume change (ΔV). The volume term is strongly relevant to conformational changes, solvation changes, and molecular recognition upon complexation and thus is relatively predictable, that is, volumetrically compact or not, compared to the complicated entropy term. These extrathermodynamic and kinetic observations prompted us to use hydrostatic pressure as a controlling factor over a long period. Hydrostatic pressure chemistry in the solution phase has developed over the past six decades and then converged and passed the fields of mechanochemistry and mechanobiology, which are new but challenging and current hot topics in multidisciplinary science. In this Account, we fully summarize our achievements in solution-state hydrostatic pressure chemistry for smart/functional molecular, supramolecular, polymer, and biological systems. We hope that the phenomena, mechanistic outcomes, and methodologies that we introduced herein for hydrostatic-pressure-controlling dynamics can provide guidance for both theoretical and experimental chemists working in supramolecular and (bio)macromolecular chemistry, mechanoscience, materials science, and technology.

A pressure-induced ratiometric signalling chemosensor: a case of helical anthracenes.

One of the helical anthracenes, [4]HA, in which two fused anthracene ends are spatially arranged top and bottom, exhibits a ratiometric fluorescence response due to the hydrostatic pressure-dependent intramolecular [4+4] photocyclodimerization. This ratiometric signalling comes from the formation of an intramolecular stacked species and its subsequent photoreaction upon hydrostatic pressurization. The ratiometric indexes as a function of hydrostatic pressure may enable us to quantify an unknown pressure in solutions.

Pressure-driven, solvation-directed planar chirality switching of cyclophano-pillar[5]arenes (molecular universal joints).

Planar chiral cyclophanopillar[5]arenes with a fused oligo(oxyethylene) or polymethylene subring (MUJs), existing as an equilibrium mixture of subring-included (in) and -excluded (out) conformers, respond to hydrostatic pressure to exhibit dynamic chiroptical property changes, leading to an unprecedented pressure-driven chirality inversion and the largest ever-reported leap of anisotropy (g) factor for the MUJ with a dodecamethylene subring. The pressure susceptivity of MUJs, assessed by the change in g per unit pressure, is a critical function of the size and nature of the subring incorporated and the solvent employed. Mechanistic elucidations reveal that the in-out equilibrium, as the origin of the MUJ's chiroptical property changes, is on a delicate balance of the competitive inclusion of subrings versus solvent molecules as well as the solvation of the excluded subring. The present results further encourage our use of pressure as a unique tool for dynamically manipulating various supramolecular devices/machines.

Directional Supramolecular Polymerization in a Dynamic Microsolution: A Linearly Moving Polymer's End Striking Monomers.

Although directional chain reactions are common in nature's self-assembly processes and in covalent polymerizations, it has been challenging to perform such processes in artificial one-dimensional self-assembling systems. In this paper, we describe a system, employing perylene bisimide (PBI) derivatives as monomers, for selectively activating one end of a supramolecular polymer during its growth and, thereby, realizing directional supramolecular polymerization. Upon introduction of a solution containing only a single PBI monomer into the microflow channel, nucleation was induced spontaneously. The dependency of the aggregation efficiency on the flow rate suggested that the shear force facilitated collisions among the monomers to overcome the activation energy required for nucleation. Next, by introducing a solution containing both monomer and polymer, we investigated how the shear force influenced the monomer-polymer interactions. In situ fluorescence spectra and linear dichroism revealed that growth of the polymers was accelerated only when they were oriented under the influence of shear stress. Upon linear motion of the oriented polymer, polymer growth at that single end became predominant relative to the nucleation of freely diffusing monomers. When applying this strategy to a two-monomer system, the second (less active) monomer reacted selectively at the forward-facing terminus of the first polymer, leading to the creation of a diblock copolymer through formation of a molecular heterojunction. This strategy-friction-induced activation of a single end of a polymer-should be applicable more generally to directional supramolecular block copolymerizations of various functional molecules, allowing molecular heterojunctions to be made at desired positions in a polymer.

Ground- and excited-state dynamic control of an anion receptor by hydrostatic pressure.

Stimulus-responsive supramolecular architectures have become an attractive alternative to conventional ones for many applications in sensing, drug-delivery and switchable memory systems. Herein, we used an anion receptor (H: host) as a hydrostatic-pressure-manipulatable fluorescence foldamer and halide anions as chiral (binaphthylammonium) and achiral (tetrabutylammonium) ion pairs (SS or RR ·X and TBA·X; X = Cl, Br), and then investigated their (chir)optical properties and molecular recognition behavior under hydrostatic pressures. The conformational changes and optical properties of H in various organic solvents were revealed by UV/vis absorption and fluorescence spectra and fluorescence lifetimes upon hydrostatic pressurization. The anion-recognition abilities of H upon interactions with SS or RR·X and TBA·X at different pressure ranges were determined by hydrostatic-pressure spectroscopy to quantitatively afford the binding constant (K anion) and apparent reaction volume changes . The results obtained indicate that hydrostatic pressure as well as solvation plays significant roles in the dynamic control of the present supramolecular system in the ground and excited states. This work will provide a new guideline for further developing hydrostatic-pressure-responsive foldamers and supramolecular materials.

Hydrostatic Pressure-Controllable Chiroptical Properties of Chiral Perylene Bisimide Dyes: A Chiral Aggregation Case.

Hydrostatically pressurized spectroscopic and lifetime decay analyses of optically active perylene bisimides were demonstrated in the pressure range of 0.1-320 MPa to show a π-stacked aggregation. The hydrostatic pressure-induced excitation and circular dichroism spectral changes of the fluorescence perylene dye enabled us to differentiate the slight pressure-sensitive aggregates. This work will lead to a new strategy for creating a pressure-responsive supramolecular polymerization material.

Complexation of an Anthracene-Triptycene Nanocage Host with Fullerene Guests through CH⋠⋠⋠π Contacts.

A bicyclic anthracene macrocycle containing two triptycene units at the bridgehead positions was synthesized by Ni-mediated coupling of the corresponding precursor as a cage-shaped aromatic hydrocarbon host. This cage host formed an inclusion complex with C60 or C70 guest in 1 : 1 ratio in solution. The association constants (Ka ) determined by the fluorescence titration method were 1.3×104 and 3.3×105  L mol -1 for the C60 and C70 complexes, respectively, at 298 K in toluene. DFT calculations revealed that the guest molecules were included in the middle of the cavity with several CH⋅⋅⋅π contacts. The strong affinity of the cage host for the fullerene guests and the high selectivity toward C70 are discussed on the basis of spectroscopic and structural data.

Hydrostatic Pressure-Regulated Cellular Calcium Responses.

Hydrostatic pressure control has attracted much attention and presents a still challenging objective from mechanobiological viewpoints. Herein, we reveal the calcium entry processes in HeLa cells by means of hydrostatic pressure spectroscopy. The steady-state fluorescence spectral data comprehensively elucidated the factors controlling the outcomes of the hydrostatic pressure-stimulated calcium entry behavior. The present work leads to a new perspective on ion regulations in living cells and an attractive alternative to conventional mechanostimuli.

The factors that govern the allosteric chemical sensing of polythiophene chemosensors: scope and limitation toward signal-amplification sensing.

The newly designed polythiophene chemosensors (PT1 and PT2) were synthesized via the Suzuki-Miyaura polymerization with appropriate yields. The photophysical properties of PTs thus obtained were examined by means of UV/vis, fluorescence, excitation spectroscopy, and time-correlated single-photon-counting method. The π-π* transitions around 400-600 nm and the emissions in the range of 400-650 nm were observed. The binding behavior of PTs was also investigated upon the interaction of tetrabutylammonium or tetrabutylphosphonium isophthalate, affording the binding constants (K) of 5790-8310 M-1, which were quite smaller than those observed in the corresponding repeating unit. The comprehensive analyses of the UV/vis data and theoretical calculation supports revealed the origins of scope and limitation toward signal-amplification sensing. The present results obtained herein will guide the development of new amplification chemosensors.

Allosteric Signal Amplification Sensing Using a Bisthiourea-Binaphthyl-Polythiophene Conjugate: A Positive Homotropic Allosterim Case.

The development of signal amplification systems has attracted much attention and presents a highly challenging objective. Herein, we reveal the amplification processes using a newly synthesized bisthiourea-binaphthyl-polythiophene conjugate. The spectral data, behavior of supramolecular complexation, and thermodynamic parameters with calculation support comprehensively elucidated the factors that control the outcomes of the signal amplification. The present work provides a new perspective on functional chemosensors and an attractive alternative to conventional amplification systems.

Multiphase Behavior of Tetraphenylethylene Derivatives with Different Polarities at High Pressures.

Although both pressure and temperature are essential parameters governing thermodynamics, the effects of the pressure on solution-phase equilibria have not been well studied compared to those of temperature. Here, we demonstrate the interesting pressure-dependent behavior of tetraphenylethylene (TPE) derivatives in multiphase systems composed of an organic phase and an aqueous phase in the presence and absence of γ-cyclodextrin (γ-CD). In this system, tetraphenylethylene monocarboxylic acid (TPE1H) and its dicarboxylic acid (TPE2H2) are distributed in the aqueous phase and dissociated into the corresponding anions, that is, TPE1- and TPE22-, when the pH is sufficiently high. The distribution ratios of TPE1H/TPE1- and TPE2H/TPE22- show opposing pressure dependencies: the distribution of the former in the organic phase increases with increasing pressure, whereas that of the latter decreases. The 1:1 complexation constants of TPE1- and TPE22- with γ-CD, which can be determined from the distribution ratios in the presence of γ-CD, also show opposing pressure dependencies: the former shows a positive pressure dependence, but the latter exhibits a negative one. These pressure effects on the distribution and complexation of TPE derivatives can be interpreted based on the differences in the molecular polarity of these solutes. The water permittivity is enhanced at high pressure, thus stabilizing the more polar TPE22- in the aqueous phase to a larger extent than TPE1- and, as a result, reducing its distribution in the organic phase, as well as its complexation with γ-CD. Fluorescence spectra in the aqueous phase suggest that the TPE derivatives form aggregates with γ-CD molecules, as detected by the specific fluorescence. In addition, the fluorescence intensities of the γ-CD complexes are enhanced at high pressures because of the restricted rotation of the phenyl rings in the TPE molecules. This study provides new perspectives for multiphase partitioning and an attractive alternative to conventional extraction methods.

Multiple Fused Anthracenes as Helical Polycyclic Aromatic Hydrocarbon Motif for Chiroptical Performance Enhancement.

Polycyclic aromatic hydrocarbons consisting of three fused anthracene units were designed as new π-conjugated compounds having helical structures. These expanded helicenes were synthesized by Pt-catalyzed cycloisomerization of the corresponding ethynyl-substituted precursors. The nonplanar and helical structure was confirmed by X-ray analysis and DFT calculations, and the barrier to helical inversion was estimated to be 34 kJ mol-1 . The enantiomers of the diphenyl derivative were successfully resolved by chiral HPLC. Enantiopure samples showed good chiroptical performance in the CD (|Δϵ| 1380 L mol-1 cm-1 ) and CPL (|glum | 0.013) spectra, and these values were considerably large for simple organic molecules. The unique chiroptical properties are discussed on the basis of the molecular structure and the electronic state with the aid of time-dependent DFT calculations.

Ice Confinement-Induced Solubilization and Aggregation of Cyanonaphthol Revealed by Fluorescence Spectroscopy and Lifetime Measurements.

When an aqueous salt solution freezes, a freeze-concentrated solution (FCS) separates from the ice. The properties of the FCS may differ from those of a supercooled bulk solution of the same ionic strength at the same temperature. The fluorescence and lifetime characteristics of 6-cyano-2-naphthol (6CN) were studied in frozen NaCl solutions in order to provide insight into the solution properties of the FCS. While the photoacidity of 6CN in an FCS is similar to that in solution, several anomalous behaviors are observed. Fluorescence spectra indicate that the solubility of 6CN is significantly enhanced in the FCS (50 mM or higher) compared to that in the bulk NaCl solution where the solubility limit is 250 µM. The high solubility induces the aggregation of 6CN in the FCS, which is not detected in bulk solutions. This trend becomes marked as the initial NaCl concentration decreases and the FCS is confined in a small space. The fluorescence lifetimes of 6CN in the FCS support the spectroscopy results. In addition to the species identified by fluorescence spectroscopy, excimers are assigned from lifetime measurements in the FCS. The excimer formation is also a result of the enhanced solubility of 6CN in the FCS.

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

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.

Frozen Solution-Mediated Asymmetric Synthesis: Control of Enantiomeric Excess.

Asymmetric List-Mannich reactions were carried out in the frozen state to afford optically active adducts in moderate-to-good chemical yields and enantiomeric excesses (ee). The frozen solution exerts critical control of ee via entropy changes, in sharp contrast to the enthalpy-driven asymmetric reactions typically observed in homogeneous solvents. This study provides new perspectives for asymmetric syntheses and an attractive alternative to conventional media.