Supramolecular Fluorescent Polymers Containing α-Cyanostilbene-Based Stereoisomers: Z/E-Isomerization Induced Multiple Reversible Switching

Abstract

Photoresponsive materials play an important role in smart sensors and readable optical devices. The α-cyanostilbene moiety gathers Z/E-isomerization, mesogenic, and aggregation-induced enhanced emission (AIEE) properties together and can be considered as a multifunctional building block bearing luminogen, AIEgen, mesogen, and chromphore characteristics. Here, we report isomerization induced a series of notable reversible switching based on α-cyanostilbene containing hydrogen-bonded supramolecular polymers. Z- and E-stereoisomers of dendritic α-cyanostilbene derivatives (Z-CNBP and E-CNBP) were hydrogen-bonded with poly­(4-vinylpyridine) (P4VP), giving rise to P4VP­(Z-CNBP) x and P4VP­(E-CNBP) x . P4VP­(Z-CNBP) x exhibit a hexagonal columnar (Φh) phase at 0.4 ≤ x ≤ 1.0, while the lamellar phase could be formed for P4VP­(E-CNBP) x at 0.3 ≤ x ≤ 0.7. P4VP­(Z-CNBP)0.8 shows photothermal E/Z-isomerization induced reversible switching, including phase structures, surface topographies, birefringence, and fluorescence properties, whereas P4VP­(E-CNBP)0.5 exhibits enhanced fluorescence emission upon UV irradiation.

Fluorescent Photochromic α‐Cyanodiarylethene Molecular Switches: An Emerging and Promising Class of Functional Diarylethene

“…Chen and coworkers reported a series of notable reversible switches based on the photothermal isomerization of α‐cyanostilbene in hydrogen‐bonded supramolecular polymers ( Figure A). [ 68a ] Two stereoisomers of an α‐cyanostilbene derivative (Z‐CNBP and E‐CNBP) and poly(4‐vinylpyridine) (P4VP) were bonded through intermolecular hydrogen bonding interactions to give rise to P4VP(Z‐CNBP) x and P4VP(E‐CNBP) x ; the former formed a hexagonal columnar (Φ h ) phase at 0.4 ≤ x ≤ 1.0, while the latter exhibited a lamellar phase at 0.3 ≤ x ≤ 0.7. Specifically, P4VP(Z‐CNBP) 0.8 showed reversible photothermal Z/E‐isomerization that induced multiple reversible switching, including self‐organized structures, surface topographies and properties, birefringence, as well as fluorescence intensity and color.…”

“…Inspired by the above‐mentioned supramolecular system, Zhang and coworkers subsequently reported P4VP(Z‐TCS) x , the first example of a supramolecular polymer based on α‐cyanostilbene that displayed photoinduced deformation (Figure 15B). [ 68b ] Supramolecular P4VP(Z‐TCS) x polymers were formed from P4VP and Z‐TCS, an α‐cyanostilbene derivative, by hydrogen‐bonding, in which the former acted as the main chain and the later acted as the side groups. Compared to P4VP(Z‐CNBP) x , the chemical structure of P4VP(Z‐TCS) x reduced one benzene ring, whose purpose was to lower the glass transition temperature ( T g ) of the supramolecular polymer.…”

“…Adapted with permission. [ 68a ] Copyright 2018, American Chemical Society. B) Photographs and schematic representation of the photoinduced bending, shape elimination by external force and shape recovery by heating of P4VP(Z‐TCS)0.6 fiber.…”

Recent synthetic advances in pyridine-based thermotropic mesogens

“…Zhu et al 122 prepared a-cyanostilbene containing hydrogen bonded supramolecular polymers. 3,4,5-trihydroxybenzaldehyde (369) monohydrate was dissolved in dry DMF; to this solution, K 2 CO 3 and KI were added, and the mixture was stirred at 80 C. To this reaction mixture, 1-bromododecane (370) was added dropwise; then, the reaction was continued overnight.…”

Polymer conformation in supramolecular complexes with wedge-shaped ligands: Exploring the impact of the liquid-crystalline organization

“…In case of smectic structures the macromolecules form oblate Gaussian coils with repartitioning of the backbones between the neighboring mesogen layers. It is well documented that macromolecules bearing wedge-shaped side groups can form columnar structures, and the self-assembly of these monodendron-side groups in a cylindrical structure can induce formation of a disordered helical conformation of the polymer backbone [12][13][14].…”