Stiff-Stilbene Photoswitches: From Fundamental Studies to Emergent Applications

Stiff-stilbene, a sterically restricted fused ring analogue of stilbene, has been regularly used as a model compound in theoretical studies of stilbene photoisomerization. Lately, owing to its excellent photoswitching properties, it is increasingly being applied to reversibly control the properties and function of chemical as well as biological systems. Stiff-stilbene photoswitches possess a number of advantageous properties including a high quantum yield for photoisomerization and a high thermal stability. Furthermore, they undergo a large geometrical change upon isomerization and their synthesis is straightforward. Herein, we provide an overview of the basic properties of stiff-stilbene and of recent applications in supramolecular chemistry, catalysis, and biological systems.     

Push-Pull Stiff-Stilbene: Proton-Gated Visible-Light Photoswitching and Acid-Catalyzed Isomerization

Donor-acceptor substituted stiff-stilbene is shown to undergo isomerization induced by visible light avoiding the need for harmful UV light. This visible-light photoswitching is inhibited by protonation of the dimethylamino-donor unit, disrupting the push-pull character and thus, gating of the photochromic properties is allowed by acid/base addition. Remarkably, the addition of a mild acid also triggers fast thermal back-isomerization, which is unprecedented for stiff-stilbene photoswitches usually having a very high energy barrier for this process. These combined features offer unique orthogonal control over switching behavior by light and protonation, which is investigated in detail by ¹H NMR and UV/Vis spectroscopy. In addition, TD-DFT calculations are used to gain further insight into the absorption properties. Our results will help elevating the level of control over dynamic behavior in stiff-stilbene applications.     

Dynamic Inversion of Stereoselective Phosphate Binding to a Bisurea Receptor Controlled by Light and Heat

A chiral bisurea anion receptor, derived from a first‐generation molecular motor, can undergo photochemical and thermal isomerization operating as a reconfigurable system. The two possible cis configurations in the isomerization cycle are opposite in helicity, as is shown by CD spectroscopy. ¹H NMR titrations demonstrate that the P and M helical cis isomers hold opposite enantioselectivity in the binding of binol phosphate, while anion complexation by the intermediate trans isomer is not selective. The difference in the binding affinity of the enantiomers was rationalized by DFT calculations, revealing very distinct binding modes. Thus, the enantiopreferred substrate binding in this receptor can be inverted in a dynamic fashion using light and heat.     

A Synthetic Supramolecular Receptor for the Hydrosulfide Anion

Hydrogen sulfide (H₂S) has emerged as a crucial biomolecule in physiology and cellular signaling. Key challenges associated with developing new chemical tools for understanding the biological roles of H₂S include developing platforms that enable reversible binding of this important biomolecule. The first synthetic small molecule receptor for the hydrosulfide anion, HS^?, using only reversible, hydrogen‐bonding interactions in a series of bis(ethynylaniline) derivatives, is reported. Binding constants of up to 90 300±8700 m ^?1 were obtained in MeCN. The fundamental science of reversible sulfide binding, in this case featuring a key CH???S hydrogen bond, will expand the possibility for discovery of sulfide protein targets and molecular recognition agents.     

Stiff‐Stilbene Photoswitches: From Fundamental Studies to Emergent Applications

Stiff‐stilbene, a sterically restricted fused ring analogue of stilbene, has been regularly used as a model compound in theoretical studies of stilbene photoisomerization. Lately, owing to its excellent photoswitching properties, it is increasingly being applied to reversibly control the properties and function of chemical as well as biological systems. Stiff‐stilbene photoswitches possess a number of advantageous properties including a high quantum yield for photoisomerization and a high thermal stability. Furthermore, they undergo a large geometrical change upon isomerization and their synthesis is straightforward. Herein, we provide an overview of the basic properties of stiff‐stilbene and of recent applications in supramolecular chemistry, catalysis, and biological systems.     

A Flexible Solution to Anion Transport: Powerful Anionophores Based on a Cyclohexane Scaffold

Transmembrane anion carriers (anionophores) have potential for biological activity, including the treatment of channelopathies such as cystic fibrosis. A new family of anionophores has been synthesized, in which three thiourea groups are mounted on a cyclohexane‐based scaffold. Though conceptually related to earlier polycyclic systems, these molecules are simpler and far more accessible. Preorganization is somewhat reduced compared to earlier systems, and anion affinities are correspondingly lower. However, transport activities set new records. This surprising performance suggests a role for controlled flexibility in the design of transmembrane anion carriers.     

Study on Synthesis and Binding Ability of a New Anion Receptor Containing NH Binding Sites

A new colorimetric recognition receptor 1 based on the dual capability containing NH binding sites of selectively sensing anionic guest species has been synthesized. Compared with other halide anions, its UV/Vis absorption spectrum in dimethyl sulfoxide showed the response toward the presence of fluoride anion with high selectivity, and also displayed dramatic color changes from colorless to yellow in the presence of TBAF （5 × 10^-5 mol/L）. The similar UV/Vis absorption spectrum change also occurred when 1 was treated with AcO^- while a little change with H2PO^-4 and OH^-. Receptor 1 has almost not affinity abilities to Cl^-, Br^- and I^-. The binding ability of receptor 1 to fluoride with high selectivity over other halides contributes to the anion size and the ability of forming hydrogen bonding. While the different ability of binding with geometrically triangular （AcO^-）, tetrahedral （H2PO^-4 ） and linear （OH^-） anions maybe result from their geometry configuration.     

基于脲衍生物阴离子识别的电化学检测

作为优良的氢键给予体,脲基(-NH-CO-NH-)是构筑阴离子识别受体的理想结构单元.而电化学方法因其方便快捷、灵敏度高等优点,近年来被广泛应用于阴离子的识别检测.本文对脲类受体的电化学阴离子识别进行了讨论,主要包括:(i) 归纳整理了电化学阴离子识别的机理,包括识别位点与阴离子结合之后对氧化还原中心的5种扰动机理和溶液中电化学测试受体和阴离子相互作用时常见现象的分析及对应结合常数的计算; (ii) 电活性脲类阴离子受体的研究进展,包括受体分子的设计、识别和机理; (iii) 探讨了该领域的后续发展方向.     

Stereodivergent Anion Binding Catalysis with Molecular Motors

A photoresponsive chiral catalyst based on an oligotriazole‐functionalized unidirectional molecular motor has been developed for stereodivergent anion binding catalysis. The motor function controls the helical chirality of supramolecular assemblies with chloride anions, which by means of chirality transfer enables the enantioselective addition of a silyl ketene acetal nucleophile to oxocarbenium cations. Reversal of stereoselectivity (up to 142 % Δee) was achieved through rotation of the motor core induced by photochemical and thermal isomerization steps.     

杯芳烃衍生物对阴离子的识别作用

综述了杯芳烃衍生物对阴离子识别作用的研究进展。详细介绍了杯芳烃衍生物的化学结构修饰和分子结构以及其通过氢键和静电等作用对卤素、有机酸根、金属酸根等阴离子的识别作用,并对其应用前景进行了展望。     

Gels Based on Anion Recognition Between Triurea Receptor and Phosphate Anion

Anion recognition between the triurea receptor and phosphate anion is demonstrated as the cross‐linkage to build supramolecular polymer gels for the first time. A novel multi‐block copolymer ( 3) is designed to have functional triurea groups as cross‐linking units along the polymer main chain. By virtue of anion coordination between the triurea receptor and phosphate anion with a binding mode of 2:1, supramolecular polymer gels are then prepared based on anion recognition using 3 as the building block.

     

Amidocrownophanes as Anion Receptor

Crownophanes composed of 28-membered ring atoms having two hydroxy groups, two amide groups, and aromatic parts such as naphthalene rings and either pyridine or benzene ring, can bind anions with high affinity and selectivity. The anion-coordination ability of these species has been observed by ¹H NMR techniques. As anion guest molecules, we selected some halides, dihydrogenphosphate and acetate ions. It has been found that amidocrownophanes, 3 and 4, can recognize anions in the order;H₂PO ₄ ⁻ >F⁻>CH₃COO⁻>Cl⁻>>Br⁻ and I⁻, while not only 1, 2, and 5 having no hydroxy group but also 6 having 27-membered ring have no ability for anion recognition under the same conditions. In order to exhibit the recognition ability for anion receptor, plural amide groups, hydroxy groups, and m-phenylene or 1,6-pyridyl rigid part play an important role in this macrocyclic system.     

氨基硫脲分子钳的合成及对阴离子的识别作用

合成了2个新型氨基硫脲分子钳主体3a(1,3-二（o-甲苯氧乙酰氨基硫脲甲酰基）苯)和3b(1,3-二（p-甲苯氧乙酰氨基硫脲甲酰基）苯),利用UV-Vis和1H NMR测试其对F-、AcO-、Cl-、Br-和I-的阴离子识别性质。 结果表明,主体分子在DMSO溶液中对F-和AcO-表现出明显的选择性识别。 1H NMR光谱证明,主体分子与阴离子之间以氢键相结合,结合Job曲线得出主体分子与阴离子之间形成1∶1型氢键缔合物。 讨论了NH识别位点数及空间结构对识别性质的影响。 与硫脲对比,主体3a具有多个NH结合位点,可形成多个氢键,结合常数（Ks）更大。 与化合物3b相比,主体3a较大的空间位阻阻碍了其与阴离子的结合,因此两种主体分子与F-和AcO-结合常数均体现为Ks(F-)＞Ks(AcO-)。     

Molecular Ionics of Anion Receptor Molecules: A Microcalorimetric Study

The coordination of divalent and monovalent inorganic anions to synthetic polyammonium receptors is investigated in aqueous solution around neutral pH by titration calorimetry and NMR spectroscopy. High-affinity 1:1 complexes are formed by a pyrrole type cryptand (1) with sulfate and phosphate, characterized by association constants of almost 107 M^-1. Affinities close to 105 M^-1 are found for polyazacryptands (3 and 4) exhibiting F^-/Cl^- selectivity. The binding affinities and the anion selectivities are mainly caused by the charges of ligands and anions, which is discussed on the basis of simple calculations of the electrostatic contribution to the anion/receptor interactions. The binding of all investigated anions is exothermic at 298.2 K. The contribution of the large negative ΔH values to the free energy of anion binding of the pyrrole type ligand is partially compensated by marked negative ΔS values. These unfavorable entropic contributions are attributed to the additional inclusion of water molecules in the anion/receptor complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

芳酰基硫脲受体的合成及对阴离子识别研究

设计合成了3种芳酰基硫脲受体分子. 利用紫外-可见吸收光谱考察了其与F^－, Cl^－, Br^－, AcO^－, HSO₄^－, H₂PO₄^－等阴离子的作用. 结果表明该类受体分子与阴离子形成氢键配合物. 加入F^－, AcO^－时, 溶液立刻由无色变为黄色, 而加入其它阴离子则无变化, 从而实现对这两种阴离子的裸眼识别. 结果表明受体分子与阴离子间形成1∶1型的配合物. ¹H NMR滴定及质子溶剂效应为受体分子与阴离子间的氢键作用本质提供了直接依据.     

Thiourea Based Tweezer Anion Receptors for Selective Sensing of Fluoride Ions

Three 3,3＇-di（4-substituted-phenyl）-1,1＇-isophthaloylbis（thiourea） compounds were designed as novel neutral anion receptors, and synthesized by simple steps in good yields. The single crystal structure of receptor 1 shows that a solvent molecule was captured by the host molecule through intermolecular hydrogen bonding. Moreover, it was self-assembled as a supramolecular system for the presence of abundant inter- and intramolecular hydrogen bonding and π-π interactions between phenyl groups. Their application as anion receptors has been examined by UV-Vis and ^1H NMR spectroscopy, showing that they had a higher selectivity for fluoride than other halides. The host and guest formed a 1 ： 1 stoichiometry complex through hydrogen bonding interactions in the first step, then following a process of deprotonation in presence of an excess of F^- in the solvent of DMF.     

一种能选择性识别磷酸根离子的金属配合物化学敏感器

合成了两种Schiff碱类金属配合物1([Cu(L1)]²⁺)和2([Cu(L2)]²⁺).对它们在强极性溶剂,如[V(水):V(乙醇)=98:2]混合溶剂中与阴离子间的相互作用进行了研究.发现具有C_3v结构的配合物1有着优良的检测PO₄^3-离子的能力.通过UV光谱滴定实验,表明配合物1和PO₄^3-间形成了1:1的稳定配合物.配合物1对HPO₄^2-也有一定的响应性.但对其它的阴离子(如四面体和非四面体结构的阴离子)物种,则未观察到有任何响应.文中还提出了配合物1与阴离子间构成新的配合物可能结构的建议.但是对于配合物2,对阴离子的响应能力比较差.对于实验结果以及如何提高敏感器化合物的选择能力进行了初步讨论.     

Halide Anion Mediated Dimerization of a meso‐Unsubstituted N‐Confused Porphyrin

The new N‐confused porphyrin (NCP) derivatives, meso‐unsubstituted β‐alkyl‐3‐oxo N‐confused porphyrin (3‐oxo‐NCP) and related macrocycles, were synthesized from appropriate pyrrolic precursors by a [3+1]‐type condensation reaction. 3‐Oxo‐NCP forms a self‐assembled dimer in dichloromethane that is stabilized by complementary hydrogen‐bonding interactions arising from the peripheral amide‐like moieties. The protonated form of 3‐oxo‐NCP was observed to bind halide anions (F^?, Cl^?) through the outer NH and the inner pyrrolic NH groups, thus affording a dimer in dichloromethane. The structure of the chloride‐bridged dimer in the solid state was determined by X‐ray diffraction analysis.