Effect of chemical substitution on the construction of boroxine-based supramolecular crystalline polymers featuring B←N dative bonds

Abstract

B←N dative bond-associated molecular to polymeric crystals have been synthesized by tuning their electronic features. The supramolecular and quantum crystallographic aspects of the B←N dative bonds were thoroughly investigated.

Photomechanical Motions in Organoboron-Based Phosphorescent Molecular Crystals Driven by a Crystal-State [2 + 2] Cycloaddition Reaction

“…46,47 In this context, the MacGillivray group initially showed the exploitation of donor−acceptor type B←N dative bonds in constructing molecular crystals that undergo intermolecular photocycloadditions but without dynamic effects. 48,49 Following their work and our continuing efforts toward the noncovalent synthesis of functional organoboronbased crystalline materials, 50 we report here photomechanical single crystals of a substituted triphenylboroxine and 1,2-di(4pyridyl)ethylene based adduct (BN1) via utilization of flexible B←N dative bonds that support intramolecular [2 + 2] cycloaddition in the crystal state and polymerization of the photoproduct during solution crystallization (Scheme 1). Remarkably, depending on the morphology and size, the dynamic crystals of BN1 undergo diverse prompt photomechanical events such as controllable bending and reshaping, jumping, delaminating, splitting, and expanding when exposed to UV.…”

“…Such mechanical motions and photoreactivity in crystals triggered by [2 + 2] cycloaddition reactions have been recently reviewed by Khan et al, 2021, and Rath et al, 2022. , Tremendous effort has been made in the past few years to design and develop photodynamic molecular crystals driven by solid-state [2 + 2] reactions. Generally, in such photodynamic crystalline materials, the solid-state reactions are directed either by energetically weak noncovalent interactions (hydrogen, halogen, and molecular stacking) or by relatively strong metal-coordinated bonds. − , To the best of our knowledge, single-crystal motility, triggered by topochemical reactions for organoboron-based molecular materials, has never been reported, although the design and execution of stimuli responsive boron compounds, having integrated photoemission and mechanical properties, are considered highly desirable for the construction of next-generation smart materials. , In this context, the MacGillivray group initially showed the exploitation of donor–acceptor type B←N dative bonds in constructing molecular crystals that undergo intermolecular photocycloadditions but without dynamic effects. , Following their work and our continuing efforts toward the noncovalent synthesis of functional organoboron-based crystalline materials, we report here photomechanical single crystals of a substituted triphenylboroxine and 1,2-di­(4-pyridyl)­ethylene based adduct (BN1) via utilization of flexible B←N dative bonds that support intramolecular [2 + 2] cycloaddition in the crystal state and polymerization of the photoproduct during solution crystallization (Scheme ). Remarkably, depending on the morphology and size, the dynamic crystals of BN1 undergo diverse prompt photomechanical events such as controllable bending and reshaping, jumping, delaminating, splitting, and expanding when exposed to UV.…”

Modular Design and Bonding Mechanism of Internal Boron–Nitrogen Coordinated Boronic Ester Hydrogels with Alkaline pH Responsiveness and Tunable Gelation pH

“…The research we have done suggests that the pH required to form an ideal IBNCB hydrogel should be greater than the p K a‑acid in phenylboronic acid compounds but lower than the p K a‑amine in N , N -bis­(2-hydroxyethyl) compounds (p K a‑acid < pH < p K a‑amine , Figure A). , Under the above pH conditions, the boron atom on phenylboronic acid is converted from the neutral, trigonal planar sp 2 hybridization state to the anionic, tetrahedral sp 3 state, while the nitrogen atom on the N , N -bis­(2-hydroxyethyl) is protonated. The boron anion and the nitrogen cation attract each other by electrostatic interaction, − followed by the loss of a water molecule and then formation of a boron–nitrogen coordination bond. , Finally, an IBNCB bond is produced.…”

“…One reason for the difficult gelation between PEI-B and PEI-N could be that the formation mechanism of the IBNCB bond , varies from that of the conventional boronic ester bond. , As shown in Figure D, when PEI-N was mixed with PEI-B, the electrostatic repulsion between the amino groups on the two backbone chains dominated. The electrostatic attraction between the phenylboronic acid and the N , N -bis­(2-hydroxyethyl) was relatively insignificant. − Thus, the formation of a homogeneous IBNCB bond cross-linked network was challenging, and all mixtures presented a delamination phenomenon. The cross-linking of conventional boronic esters does not involve the contradictory electrostatic attraction and electrostatic repulsion.…”

N-Coordinated Organoboron in Polymer Synthesis and Material Science

“…The combination of boron−nitrogen coordination and other noncovalent interactions is also an important route to preparing supramolecular networks. 108 In 2010, Aoi and coworkers prepared novel supramolecular-type solid polymer electrolytes on the basis of the self-assembly of a diborylated ionic liquid and bifunctional ligands (Figure 20a). 109 In the presence of the equimolar amount of LiTFSA to the ionic liquid unit, these polymers in the solid state showed good ionic conductivity.…”