The conformation and electronic structure of dibenzo-24-crown-8 (DB24C8) complexes with K + ion were examined by ion mobility−mass spectrometry (IM−MS), ultraviolet (UV) photodissociation (UVPD) spectroscopy in the gas phase, and fluorescence spectroscopy in solution. Three structural isomers of DB24C8 (SymDB24C8, Asym1DB24C8, and Asym2DB24C8) in which the relative positions of the two benzene rings were different from each other were investigated. The IM−MS results at 86 K revealed a clear separation of two sets of conformers for the K + (SymDB24C8) and K + (Asym1DB24C8) complexes whereas the K + (Asym2DB24C8) complex revealed only one set. The two sets of conformers were attributed to the open and closed forms in which the benzene−benzene distances in the complexes were long (>6 Å) and short (<6 Å), respectively. IM−MS at 300 K could not separate the two conformer sets of the K + (SymDB24C8) complex because the interconversion between the open and closed conformations occurred at 300 K and not at 86 K. The crown cavity of DB24C8 was wrapped around the K + ion in the complex, although the IM−MS results availed direct evidence of rapid cavity deformation and the reconstruction of stable conformers at 300 K. The UVPD spectra of the K + (SymDB24C8) and K + (Asym1DB24C8) complexes at ∼10 K displayed broad features that were accompanied by a few sharp vibronic bands, which were attributable to the coexistence of multiple conformers. The fluorescence spectra obtained in a methanol solution suggested that the intramolecular excimer was formed only in K + (SymDB24C8) among the three complexes because only SymDB24C8 could possibly assume a parallel configuration between the two benzene rings upon K + encapsulation. The encapsulation methods for K + ion (the "wraparound" arrangement) are similar in the three structural isomers of DB24C8, although the difference in the relative positions of the two benzene rings affected the overall cross-section. This study demonstrated that temperature-controlled IM−MS coupled with the introduction of appropriate bulky groups, such as aromatic rings to host molecules, could reveal the dynamic aspects of encapsulation in host−guest systems.

We herein describe a new design principle to achieve B/N-doped cyclophane where an electron-donor block of three triarylamines (Ar 3 N) and an acceptor block of three triarylboranes (Ar 3 B) are spatially separated on opposite sides of the π-extended ring system. DFT computations revealed the distinct electronic structure of the block-type macrocycle MC-b-B3N3 with a greatly enhanced dipole moment and reduced HOMO-LUMO energy gap in comparison to its analogue with alternating B and N sites, MC-alt-B3N3. The unique arrangement of borane acceptor Ar 3 B and amine donor Ar 3 N components in MC-b-B3N3 induces exceptionally strong intramolecular charge transfer in the excited state, which is reflected in a largely red-shifted luminescence at 612 nm in solution.The respective linear open-chain oligomer L-b-B3N3 was also synthesized for comparison. Our new approach to donor-acceptor macrocycles offers important fundamental insights and opens up a new avenue to unique optoelectronic materials.

Polycationic macrocycles are attractive as they display unique molecular switching capabilities arising from their redox properties. Although diverse polycationic macrocycles have been developed, those based on cationic boron systems remain very limited. We present herein the development of novel polycationic macrocycles by introducing organoboronium moieties into a conjugated organoboron macrocyclic framework. These macrocycles consist of four bipyridylboronium units that are connected by fluorene and either electron-deficient arylborane or electron-rich arylamine moieties. Electrochemical studies reveal that the macrocycles undergo reversible multi-step redox processes with transfer of up to 10 electrons. Switchable electrochromic behavior is demonstrated via spectroelectrochemical studies and the observed color changes are rationalized by correlation with computed electronic transitions using DFT methods.Endowed with unique electrooptical characteristics, conjugated polycations serve as important components in the fields of supramolecular materials and redox-responsive systems. [1] Among them, polycationic macrocycles such as Stoddarts "blue box" [2] generate impressive interlocked structures and exhibit unique molecular switching capabilities. [3] Since their first discovery, numerous derivatives have been synthesized and utilized in supramolecular assemblies, host-guest chemistry, [4] molecular electronics, [5] electron transfer, [6] and electrochromic [7] materials. Although diverse polycationic macrocycles have been reported, [8] those based on cationic boronium moieties remain very limited. [9] Very recently, coordination-driven self-assembly to build up polycationic boron macrocycles was reported by Himmel and co-workers. [9c] These macrocycles are composed of cationic diborane units that are linked together by pyrazine, 4,4'-bipyridine, or 1,2di(4-pyridyl)ethene.Over the course of our studies on organoboron pconjugated materials, [10] we developed a unique class of boracyclophanes with strongly Lewis acidic boron sites, including ambipolar borazine A [11] with its alternating electron-deficient arylboranes and electron-rich arylamines and the highly electron-deficient macrocycles B [12] (Figure 1 a). [13]

Boron-containing molecules and polymers are attractive as powerful tunable Lewis acids for small molecule activation and catalysis, as luminescent materials for organic electronic device and (bio)imaging applications, and as smart chemical sensors. While the characteristics of the boron-containing building blocks are attractive in and of themselves, their assembly into higher order supramolecular materials offers access to unique properties and emerging functions. Herein, we highlight recent achievements in the field of aggregated organoboron materials. We discuss how supramolecular interactions can be exploited to precisely control the structure of the assemblies and impact their functions as luminescent materials, recyclable and smart catalyst systems, chemical sensors, stimuli-responsive and self-healing materials.

Bisresorcinarenes 1a-d were obtained in excellent yields, and 1e was finally obtained in 50% yield. X-ray diffraction analysis showed that 1a and 1b adopted helical conformations, whereas the two resorcinarenes of 1c-e were in parallel orientations in which the clefts of the aliphatic chains entrapped one or two solvent molecules. The conformational study revealed that the helix interconversion between the (P)- and (M)-helical conformers depended on the length of the aliphatic chains. 1a had the largest energetic barrier to helix interconversion, while in 1b, its more flexible aliphatic chains lowered its energetic barriers. The P/M interconversion of 1a was coupled with the clockwise/anticlockwise interconversion of the interannular hydrogen bonding of the two resorcinarenes. The large negative entropic contributions indicate that the transition state is most likely more ordered than the ground states, suggesting that the transition state is most likely symmetric and is solvated by water molecules. Calculations at the M06-2X/6-31G(d,p) level revealed that the more stable (P)-conformation has clockwise interannular hydrogen bonding between the two resorcinarenes.

Although a wide variety of boron-based “scorpionate” ligands have been implemented, a modular route that offers facile access to different substitution patterns at boron has yet to be developed. Here,...

Uncommon entropy‐driven cooperativity is reported in the guest binding of an octaphosphonate bis‐cavitand. Isothermal titration calorimetry determined the thermodynamic parameters for the 1:2 host–guest binding of bis‐cavitands with ammonium guests in methanol, ethanol, 2‐propanol, and chloroform. Chloroform drove uncommon entropy‐driven cooperative binding, whereas the alcohols resulted in enthalpy‐driven noncooperative binding. 1H NMR studies revealed that each cavity contained six water molecules in chloroform, which were liberated on guest binding. The enthalpy–entropy compensation relationship produced a large positive intrinsic entropy in chloroform, which implies that water desolvation causes a considerable entropic gain by paying an enthalpic penalty due to breaking the hydrogen‐bonding networks of the water clusters.

Rim‐to‐rim‐connected phosphonate biscavitands 1a and 1b were synthesized. Crystal structure analysis and variable‐temperature NMR spectroscopy studies reveal that 1a is more rigid in conformation than 1b. Biscavitands 1a and 1b bind cationic guests G1–G3 through hydrogen bonding and CH–π interactions, demonstrating positive and negative allosteric effects, respectively. The allosteric effects in guest binding are associated with the conformational flexibilities of 1a and 1b. The positive allosteric effect of 1a is directed by the tightly connected cavities, in which information of the first guest binding is transferred to the remaining cavity, which becomes preorganized. In contrast, a slightly negative allosteric effect is found in more‐flexible 1b.