Reversible Stereoselective Folding/Unfolding Fueled by the Interplay of Photoisomerism and Hydrogen Bonding

Abstract

A linear molecular architecture equipped with complementary three-fold hydrogen-bonding units embedded with a photoswitchable trans-tetrafluoroazobenzene moiety was synthesized. The transto cis photoisomerism of the azobenzene unit induced drastic changes in the molecular architecture as a result of intramolecular hydrogen bonding as evidenced by NMR spectroscopy and size exclusion chromatography. A minute stereogenic element in the linear trans state enabled stereoselective folding into the cis state, thus producing a globular architecture with enhanced chiroptical property.

“Urea to Urea” Approach: Access to Unsymmetrical Ureas Bearing Pyridyl Substituents

“…Particularly, many recent studies focus on the utilization of 2‐pyridylurea‐based compounds as ion sensors, [28–32] ligands of organometallic catalysts for polysiloxanes production, [33,34] self‐assembled biomimetic materials for electron‐rich species transmission, [35] agents for polymer functionalization through multiple hydrogen bonding, [36] and antibacterial supramolecular gels [37] . Furthermore, the successful utility of pyridylurea derivatives in the synthesis of foldamers with improved chiroptical properties has been shown [38,39] …”

“…[37] Furthermore, the successful utility of pyridylurea derivatives in the synthesis of foldamers with improved chiroptical properties has been shown. [38,39] The most practically significant synthetic route toward unsymmetrical 1,3-disubsituted ureas is the nucleophilic addition of amines to isocyanates. [40][41][42][43][44] The drawback of this approach is the inherent isocyanate toxicity and harmfulness.…”

Towards photoswitchable quadruple hydrogen bonds via a reversible “photolocking” strategy for photocontrolled self-assembly

“…50 The Yagai group has also developed a series of multiple H-bonds directed supramolecular toroidal building blocks to fabricate unique supramolecular polymeric systems with photoregulable topologies. 18,56 Nevertheless, including these examples, most of the reported photoresponsive multiple H-bonded systems have been designed on the basis of molecular geometric variations of the building blocks which are induced by the photoisomerization of incorporated photochromophores, [48][49][50][51][52][53][54][55][56] rather than directly photoswitching the association constants of multiple H-bonding interactions. However, impeded by the diversity in structures and bonding modes of multiple H-bonding motifs, as well as the strong structural matching requirement of multiple H-bonding interactions, it is challengeable to develop a general strategy for the construction of multiple H-bonding motifs with sufficiently photoswitchable H-bonding affinities.…”

“…[19][20][21] Over the past few decades, great efforts have been devoted to the development of complementary multiple H-bonding motifs. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Meanwhile, by taking advantage of the stimuli-responsive nature of H-bonding interactions, considerable attention has been focused on the development of tunable H-bonded selfassemblies and materials with responsiveness to external stimuli such as temperature, 38,39 pH, 32,[40][41][42] redox, [43][44][45][46] light, [47][48][49][50][51][52][53][54][55][56] and competitive guests. 57,58 Compared to other stimuli, light has been recognized to be ideal due to its cleanness and unique spatiotemporal resolution, [59][60][61][62] beneting from which various sophisticated photoresponsive H-bonded systems have been constructed.…”

Binary Supramolecular Gel of Achiral Azobenzene with a Chaperone Gelator: Chirality Transfer, Tuned Morphology, and Chiroptical Property

“…Supramolecular gels from the self-assembly of small organic molecules in organic solvents (organogel) or water (hydrogel) have attracted extensive research interest in past decades as a result of their easy design, controlled nanostructure, and wide scope of applications including optoelectronic devices, sensing systems, catalysis, tissue engineering, and biomaterials. − Among these applications, the reversible chiroptical materials, i.e., optical materials with reversible chirality, are currently attracting great interest, , in which the gel materials can provide many opportunities. Azobenzene, as one of the most widely investigated photoactive building blocks, is a major candidate for forming chiroptical materials. , To fabricate chiroptical materials based on azobenzene, it is necessary to introduce the chiral component into the system. The most common strategy is to synthesize new gelators in which the azobenzene moiety and chiral component are covalently linked together.…”