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

Tomokazu Kinoshita,Yohei Haketa,Hiromitsu Maeda,Gaku Fukuhara

doi:10.1039/d1sc00664a

Abstract

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 (Kanion) 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.

Highlights

We have recently revealed that optical properties, molecular and biomolecular recognition behavior and photo-physical/chemical processes in solutions of various molecular, supramolecular, macromolecular and biomacromolecular systems are precisely regulated by hydrostatic pressure.[53,54,55,56,57,58,59,60,61,62,63]
To apply the hydrostatic pressurecontrol concept to chemical sensing of foldamers in solutions, we chose a combination of an anion receptor (H: host) as a uorescence foldamer and chiral ion pairs (SS or RR$X) as guests, as shown in Fig. 2a and b, and investigated their optical properties and molecular recognition behavior upon hydrostatic pressurization
Solutions of H were prepared by dissolving in toluene, chloroform, dichloromethane and acetonitrile (ET: 33.9–45.6 kcal molÀ1), and subjected to hydrostaticpressurized UV/vis absorption (Fig. 3, le panels), uorescence (Fig. 3, right panels) and excitation spectroscopies (Fig. S2 in the Electronic supplementary information (ESI)†)

Summary

Introduction

A large number of chemosensors, pre-organized hosts and supramolecular assemblies/polymers have been exploited in a rather long history since the great discovery of crown ethers in 1967.1–3 Today, sophisticated supramolecular materials triggered by a wide variety of external stimuli, e.g., temperature, solvent, pH or electronic excitation, have been developed to achieve “molecular machines” that can alter the molecular-level structure/function/properties.[4,5,6] Even apart from such arti cial molecular machines, the creation of stimulus-responsive supramolecular architectures is a recent great trend for some applications in chemical and apoptosis sensing,[7,8,9,10,11,12] drugdelivery[13,14,15] and switchable memory systems.[16,17,18,19]Hydrostatic pressure, one of the mechanical stimuli, has attracted attention for a long time since the early 1960s,20–27 since hydrostatic pressurization of object solutions can controlTo this end, we focus on foldamers as arti cial receptors or chemosensors which are a type of synthetic oligomers that show dynamic folded and unfolded states in solutions.[64]. To apply the hydrostatic pressurecontrol concept to chemical sensing of foldamers in solutions, we chose a combination of an anion receptor (H: host) as a uorescence foldamer and chiral ion pairs (SS or RR$X) as guests, as shown in Fig. 2a and b, and investigated their (chir) optical properties and molecular recognition behavior upon hydrostatic pressurization.

Results

Conclusion