Light-melt adhesive based on dynamic carbon frameworks in a columnar liquid-crystal phase

Fully Recycled Polyolefin Elastomer-Based Vitrimers with Ultra-High, Universal, Stable, and Switchable Adhesion

Achieving both robust adhesion to arbitrary surfaces and thermal-switchable/recyclable properties has proven challenging, particularly for commodity polyolefins. Herein, a simple and effective route is reported to transform polyolefins elastomer (POE) into a fully recycled epoxy-functionalized POE vitrimers (E-POE vit) with ultra-high, universal, stable, and switchable adhesion via facile free radical grafting and dynamic cross-linking. The resultant E-POE vit exhibits increase in adhesion strength on glass exceeding three to ten times compared to those commonly used polymers, due to the synergy of dense hydrogen (H)-bonds and strong interfacial affinity. In addition, E-POE vit also displays strong adhesion on diverse surfaces ranging from inorganic to organic while maintaining good stability in various harsh environments. More importantly, temperature-sensitive H-bonds allow E-POE vit to switch between attachment-detachment at alternating temperatures, resulting in reversible adhesion without adhesion loss, even after 10 cycles. Moreover, E-POE vit is able to be fully recycled and reused more than ten times via thermo-activated transesterification reactions with negligible change in structure and performance. This work may unlock strategies to fabricate high-performance commercial polymer-based adhesives with adhesion and recyclable features for intelligent and sustainable applications.

Reversible Light-Triggered Stretching of Small-Molecule Photochromic Organic Nanoparticles

Functional organic nanomaterials are nowadays largely spread in the field of nanomedicine. In situ modulation of their morphology is thus expected to considerably impact their interactions with the surroundings. In this context, photoswitchable nanoparticles that are manufactured, amenable to extensive disassembling upon illumination in the visible, and reversible reshaping under UV exposure. Such reversibility turns to be strongly impaired for photochromic nanoparticles in close contact with a substrate. In situ atomic force microscopy investigations at the nanoscale actually reveal progressive disintegration of the organic nanoparticles under successive UV-vis cycles of irradiation, in the absence of intrinsic elastic forces. These results point out the dramatic interactions exerted by surfaces on the cohesion of non-covalently bonded organic nanoparticles. They invite to harness such systems, often used as biomarkers, to also serve as photoactivatable drug delivery nanocarriers.

Methylene Blue: An FDA-Approved NIR-II Fluorogenic Probe with Extremely Low pH Responsibility for Hyperchlorhydria Imaging

Methylene blue (MB) is an FDA (Food and Drug Administration)-approved contrast agent with donor-acceptor (D-A) structure integrated with carbonyl-containing nitrogen-heterocycles. MB can be converted into MBH (protonated MB) by protonation, which not only induces the fluorescence emission red-shifted from the first near-infrared window (NIR-I, 650-950 nm) to the second near-infrared window (NIR-II, 1000-1700 nm) but also achieves ACQ-to-AIE conversion. MB has been successfully demonstrated in hyperacidemia imaging with an extremely low pH value (<1).

Proton transfer induced excited-state aromaticity gain for chromophores with maximal Stokes shifts

Excited state aromaticity (ESA) offers a fascinating route for driving photophysical and photochemical processes but is challenging to harness fully due to its inherent association with unstable antiaromatic ground states. Here, we propose to circumvent this problem via the introduction of a new class of photophysical processes, the generation of ESA via an excited-state intramolecular proton transfer. We select twelve candidate molecules based on the cyclobutadiene and pentalene scaffolds and investigate their ground and excited state properties using computation. The study highlights the feasibility of proton transfer induced ESA gain and shows that it gives rise to pronounced excited-state relaxation producing Stokes shifts in excess of 2 eV. The underlying electronic structure properties are analysed in terms of the orbitals involved as well as aromaticity descriptors illustrating the pronounced changes these molecules undergo upon both excitation and proton transfer. In summary, we believe that the present work will pave the way toward a new class of chromophores with maximal Stokes shifts and excited-state relaxation.

Transforming Commercial Polymers into Tough yet Switchable Adhesives by Trident Photoswitch Molecule Doping: Break Adhesion-Switchability Paradox

Here, a trident molecule doping strategy is introduced to overcome both cohesion-adhesion trade-off and adhesion-switchability conflict, transforming commercial polymers into tough yet photo-switchable adhesives. The strategy involves initial rational design of new trident photoswitch molecules namely TAzo-3 featuring azobenzene and hydroxy-terminated alkyl chains involved rigid-soft tri-branch structure, and subsequent doping into commercial polycaprolactone (PCL) via simple blending. Unique design enables TAzo-3 as a versatile dopant, not only regulating the internal and external supramolecular interaction to balance cohesion and interface adhesion for tough bonding, but also affording marked photothermal effect to facilitate rapid adhesive melting for great photo-switchability. Thus, the optimal TAzo-3-doped PCL (TAzo-3@P) displays markedly-improved bonding performance on diverse substrates compared to linear azobenzene-doped PCL and pure PCL. Impressively, TAzo-3@P on polymethyl methacrylate (PMMA) attains large room-temperature adhesion strength of 6.7 MPa - surpassing most reported adhesives and many commercial adhesives on PMMA, along with easy photo-induced detachment with remarkable switch ratio of 2.09 × 105. Besides, TAzo-3@P can also act as "permanent" adhesives for only adhesion, demonstrating excellent multi-reusability, anti-freezing and waterproof ability. Mechanism studies unveil that the switchable adhesion is closely linked with the dopant molecule structure while rigid-soft coupled trident structures and hydroxy-terminated alkyl chains are key factors.

Plasmonic Hydrogel Actuators for Octopus-Inspired Photo/Thermoresponsive Smart Adhesive Patch

Octopuses are notable creatures that can dynamically adhere to a variety of substrates owing to the efficient pressure control within their suction cups. An octopus' suckers are sealed at the rim and function by reducing the pressure inside the cavity, thereby creating a pressure difference between the ambient environment and the inner cavity. Inspired by this mechanism, we developed a plasmonic smart adhesive patch (Plasmonic AdPatch) with switchable adhesion in response to both temperature changes and near-infrared (NIR) light. The AdPatch incorporates an elastic, nanohole-patterned elastomer that mimics the structure of octopus suckers. Additionally, a monolayer of gold nanostars (GNSs) is coated on the patch, facilitating a NIR light-responsive photothermal effect. A musclelike, thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel functions as a volumetric actuator to regulate cavity pressure. When exposed to heat or light, the PNIPAM hydrogel shrinks, enabling the AdPatch to achieve strong suction adhesion (134 kPa at 45 °C, 71 kPa at 85 mW cm-2). Owing to its capability to achieve light-triggered remote adhesion without the need for external pressure, the Plasmonic AdPatch can be employed to transfer ultrathin films and biosensors to fragile organs without causing damage.

Small Ionic-Liquid-Based Molecule Drives Strong Adhesives

Nature has inspired scientists to fabricate adhesive materials for applications in many burgeoning areas. However, it is still a significant challenge to develop small-molecule adhesives with high-strength, low-temperature and recyclable properties, although these merits are of great interest in various aspects. Herein, we report a series of strong adhesives based on low-molecular-weight molecular solids driven by the terminal modification of ionic liquids (ILs) and subsequent supramolecular self-assembly. The emergence of high strength and liquid-to-solid transitions for these supramolecular aggregates relies on modifying IL with a high melting point motif and enriching the types of noncovalent interactions in the original ILs. Using this strategy, we demonstrate that our IL-based molecular solids can efficiently obtain a high adhesion strength (up to 8.95 MPa). Importantly, we elucidate the mechanism underlying the reversible and strong adhesion enabled by monomer-to-polymer transitions. These fundamental findings provide guidance for the design of high-performance supramolecular adhesive materials.

Ultraviolet Light Debondable Optically Clear Adhesives for Flexible Displays through Efficient Visible-Light Curing

With growing sustainability concerns, the need for products that facilitate easy disassembly and reuse has increased. Adhesives, initially designed for bonding, now face demands for selective removal, enabling rapid assembly-disassembly and efficient maintenance across industries. This need is particularly evident in the display industry, with the rise of foldable devices necessitating specialized adhesives. A novel optically clear adhesive (OCA) is presented for foldable display, featuring a unique UV-stimulated selective removal feature. This approach incorporates benzophenone derivatives into the polymer network, facilitating rapid debonding under UV irradiation. A key feature of this method is the adept use of visible-light-driven radical polymerization for OCA film fabrication. This method shows remarkable compatibility with various monomers and exhibits orthogonal reactivity to benzophenone, rendering it ideal for large-scale production. The resultant OCA not only has high transparency and balanced elasticity, along with excellent resistance to repeated folding, but it also exhibits significantly reduced adhesion when exposed to UV irradiation. By merging this customized formulation with strategically integrated UV-responsive elements, an effective solution is offered that enhances manufacturing efficiency and product reliability in the rapidly evolving field of sustainable electronics and displays. This research additionally contributes to eco-friendly device fabrication, aligning with emerging technology demands.

Robust Supercooled Liquid Formation Enables All-Optical Switching Between Liquid and Solid Phases of TEMPO

Organic molecules that undergo supercooling can provide the basis for novel stimuli-responsive materials, but the number of such compounds is limited. Results in this paper show that the stable organic radical 2,2,6,6-tetramethyl-1-piperidine-1-oxyl (TEMPO) can form a stable supercooled liquid (SCL). Upon melting and cooling back to room temperature, the TEMPO SCL can persist for months, even after mild physical agitation. Its high vapor pressure can enable crystal growth at remote locations within the sample container over the course of days. Optical, electron paramagnetic resonance, and birefringence measurements show no evidence of new chemical species or partially ordered phases in the supercooled liquid. TEMPO's free radical character permits absorption of visible light that can drive photothermal melting to form the SCL, while a single nanosecond light pulse can initiate recrystallization of the SCL at some later time. This capability enables all-optical switching between the solid and the SCL phases. The physical origin of TEMPO's remarkable stability as an SCL remains an open question, but these results suggest that organic radicals comprise a new class of molecules that can form SCLs with potentially useful properties.

Environment-sensitive fluorescence of COT-fused perylene bisimide based on symmetry-breaking charge separation

Flexible and aromatic photofunctional system (FLAP) is composed of flapping rigid aromatic wings fused with a flexible 8π ring at the center such as cyclooctatetraene (COT). A series of FLAP have been actively studied for the interesting dynamic behaviors. Here, we synthesized a new flapping molecule bearing naphtho-perylenebisimide wings (NPBI-FLAP), in which two perylene units are arranged side by side. As a reference compound, we also prepared COT-fused NPBI (NPBI-COT) that contains only single perylene unit. In both compounds, inherent strong fluorescence of the NPBI moiety is almost quenched and the FL lifetime becomes much shortened in highly polar solvents (acetone and DMF). Through the analyses of environment-sensitive fluorescence, electrochemical reduction/oxidation, and femtosecond transient absorption, the fluorescence quenching behavior was attributed to rapid symmetry-breaking charge separation (SB-CS) for NPBI-FLAP and to intramolecular charge transfer (ICT) for NPBI-COT. Most of the excited species of these compounds decay with the bent geometry, which is in contrast with the excited-state planarization behavior of a previously reported COT-fused peryleneimides with the double-headed arrangement of the perylene moieties. These results indicate that changing the fusion manners between COT and other π skeletons offers new functional molecules with distinct dynamics.

Functionalisation of conjugated macrocycles with type I and II concealed antiaromaticity via cross-coupling reactions

Conjugated macrocycles can exhibit concealed antiaromaticity; that is, despite not being antiaromatic, under specific circumstances, they can display properties typically observed in antiaromatic molecules due to their formal macrocyclic 4n π-electron system. Paracyclophanetetraene (PCT) and its derivatives are prime examples of macrocycles exhibiting this behaviour. In redox reactions and upon photoexcitation, they have been shown to behave like antiaromatic molecules (requiring type I and II concealed antiaromaticity, respectively), with such phenomena showing potential for use in battery electrode materials and other electronic applications. However, further exploration of PCTs has been hindered by the lack of halogenated molecular building blocks that would permit their integration into larger conjugated molecules by cross-coupling reactions. Here, we present two dibrominated PCTs, obtained as a mixture of regioisomers from a three-step synthesis, and demonstrate their functionalisation via Suzuki cross-coupling reactions. Optical, electrochemical, and theoretical studies reveal that aryl substituents can subtly tune the properties and behaviour of PCT, showing that this is a viable strategy in further exploring this promising class of materials.

Photoinduced crystal melting with luminescence evolution based on conformational isomerisation

The phenomenon of crystal melting by light irradiation, known as photo-induced crystal-to-liquid transition (PCLT), can dramatically change material properties with high spatiotemporal resolution. However, the diversity of compounds exhibiting PCLT is severely limited, which hampers further functionalisation of PCLT-active materials and the fundamental understandings of PCLT. Here, we report on heteroaromatic 1,2-diketones as the new class of PCLT-active compounds, whose PCLT is based on conformational isomerisation. In particular, one of the diketones demonstrates luminescence evolution prior to crystal melting. Thus, the diketone crystal exhibits dynamic multistep changes in the luminescence colour and intensity during continuous ultraviolet irradiation. This luminescence evolution can be ascribed to the sequential PCLT processes of crystal loosening and conformational isomerisation before macroscopic melting. Single-crystal X-ray structural analysis, thermal analysis, and theoretical calculations of two PCLT-active and one inactive diketones revealed weaker intermolecular interactions for the PCLT-active crystals. In particular, we observed a characteristic packing motif for the PCLT-active crystals, consisting of an ordered layer of diketone core and a disordered layer of triisopropylsilyl moieties. Our results demonstrate the integration of photofunction with PCLT, provide fundamental insights into the melting process of molecular crystals, and will diversify the molecular design of PCLT-active materials beyond classical photochromic scaffolds such as azobenzenes.

Photo-and Heat-Induced Dismantlable Adhesion Interfaces Prepared by Layer-by-Layer Deposition

The development of a dismantlable adhesion technology that allows switching between bonding and debonding states using external stimuli is important for realizing renewable and sustainable material cycles. Controlling the adhesion interface is an effective approach to manipulate the adhesion strength; however, research on dismantlable systems focusing on the interface has not been proceeded. Recently, we demonstrated a novel dismantlable system based on a stimuli-responsive molecular layer comprising cleavable anthracene dimers, which strengthen the initial adhesive force by forming chemical bonds between the substrate and adhesive and can be dismantled when required via stimulation-induced bond breaking. Here, we evaluate the use of the anthracene-based molecular layer with different components for verifying its versatility in the adhesive/dismantling system. The formation of the cleavable molecular layer by the stacking of relevant molecules enabled its usage with two types of adhesives, an epoxy adhesive and a silane-modified polymer adhesive. The initial adhesive strengths were improved in both types of molecular layers by creating chemical bonds at the adhesion interfaces. Light irradiation or heating stimuli for 1 min reduced the peel strength by up to 65%, and dismantling occurred in the cleavable photodimer layer. This study expands the versatile applicability of the molecular layer-based dismantling system.

Fully recyclable multifunctional adhesive with high durability, transparency, flame retardancy, and harsh-environment resistance

Recyclable/reversible adhesives have attracted growing attention for sustainability and intelligence but suffer from low adhesion strength and poor durability in complex conditions. Here, we demonstrate an aromatic siloxane adhesive that exploits stimuli-responsive reversible assembly driven by π-π stacking, allowing for elimination and activation of interfacial interactions via infiltration-volatilization of ethanol. The robust cohesive energy from water-insensitive siloxane assembly enables durable strong adhesion (3.5 MPa shear strength on glasses) on diverse surfaces. Long-term adhesion performances are realized in underwater, salt, and acid/alkali solutions (pH 1-14) and at low/high temperatures (-10-90°C). With reversible assembly/disassembly, the adhesive is closed-loop recycled (~100%) and reused over 100 times without adhesion loss. Furthermore, the adhesive has unique combinations of high transparency (~98% in the visible light region of 400-800 nm) and flame retardancy. The experiments and theoretical calculations reveal the corresponding mechanism at the molecular level. This π-π stacking-driven siloxane assembly strategy opens up an avenue for high-performance adhesives with circular life and multifunctional integration.

Structural Phase Transitions in Anthracene Crystals

Anthracene (C14 H10 ) and its derivatives, π-conjugated molecules in acenes, have been widely researched in terms of their reactions, physical properties, and self-assembly (or crystal engineering). These molecules can be functionalized to tune reactivities, optoelectronic properties, and self-assembling abilities. Structural changes in the molecular assemblies, solid states, and crystals have recently been discovered. Therefore, a systematic discussion of anthracene's molecular structure, packing, and optical properties based on its intermolecular structure and phase transitions is important for future chemical and structural design. In the present review, we discuss anthracene's molecular design, dimer packing, and crystal structure, focusing on the structural phase transitions of its crystals. We also provide examples of the phase transitions of anthracene crystals. Changes to edge-to-face of CH-π interaction and face-to-face packing of π-π interaction affect the thermodynamic stabilities of various crystal structures. These structures can inform the prediction of structural and physical properties.

Copper(I) Catalyzed Decarboxylative Synthesis of Diareno[a,e]cyclooctatetraenes

Diareno[a,e]cyclooctatetraenes find widespread applications as building blocks, ligands, and responsive cores in topologically switchable materials. However, current synthetic methods to these structures suffer from low yields or operational disadvantages. Here, we describe a practical three-step approach to diareno[a,e]cyclooctatetraenes using an efficient copper(I) catalyzed double decarboxylation as the key step. The sequence relies on cheap and abundant reagents, is readily performed on scale, and is amenable also to unsymmetrical derivatives that expand the utility of this intriguing class of structures.

Sterically Frustrated Aromatic Enes with Various Colors Originating from Multiple Folded and Twisted Conformations in Crystal Polymorphs

Overcrowded ethylenes composed of 10-methyleneanthrone and two bulky aromatic rings contain a twisted carbon-carbon double (C=C) bond as well as a folded anthrone unit. As such, they are unique frustrated aromatic enes (FAEs). Various colored crystals of these FAEs, obtained in different solvents, correspond to multiple metastable conformations of the FAEs with various twist and fold angles of the C=C bond, as well as various dihedral angles of attached aryl units with respect to the C=C bond. The relationships between color and these parameters associated with conformational features around the C=C bond were elucidated in experimental and computational studies. Owing to the fact that they are separated by small energy barriers, the variously colored conformations in the FAE crystal change in response to various external stimuli, such as mechanical grinding, hydrostatic pressure and thermal heating.

Strong Dynamic Interfacial Adhesion by Polymeric Ionic Liquids under Extreme Conditions

Interfacial adhesion under extreme conditions has attracted increasing attention owing to its potential application of stopping leakages of oil or natural gas. However, interfacial adhesion is rarely stable at ultralow temperatures and in organic solvents, necessitating the elucidation of the molecular-level processes. Herein, we used the intermolecular force-control strategy to prepare four linear polymers by tuning the proportion of hydrogen bonding and the number of electrostatic sites. The obtained polymeric ion liquids displayed strong dynamic adhesion at various interfaces. They also efficiently tolerated organic solvents and ultracold temperatures. Highly reversible rheological behaviors are observed within a thermal cycle between high and ultracold temperatures. Temperature-dependent infrared spectra and theoretical calculation reveal thermal reversibility and interfacial adhesion/debonding processes at the molecular level, respectively. This intermolecular force-control strategy may be applied to produce environmentally adaptive functional materials for real applications.

Assessing Polymer-Surface Adhesion with a Polymer Collection

Polymer modification plays an important role in the construction of devices, but the lack of fundamental understanding on polymer-surface adhesion limits the development of miniaturized devices. In this work, a thermoplastic polymer collection was established using the combinatorial laser-induced forward transfer technique as a research platform, to assess the adhesion of polymers to substrates of different wettability. Furthermore, it also revealed the influence of adhesion on dewetting phenomena during the laser transfer and relaxation process, resulting in polymer spots of various morphologies. This gives a general insight into polymer-surface adhesion and connects it with the generation of defined polymer microstructures, which can be a valuable reference for the rational use of polymers.

Stimuli-responsive temporary adhesives: enabling debonding on demand through strategic molecular design

Stimuli-responsive temporary adhesives constitute a rapidly developing class of materials defined by the modulation of adhesion upon exposure to an external stimulus or stimuli. Engineering these materials to shift between two characteristic properties, strong adhesion and facile debonding, can be achieved through design strategies that target molecular functionalities. This perspective reviews the recent design and development of these materials, with a focus on the different stimuli that may initiate debonding. These stimuli include UV light, thermal energy, chemical triggers, and other potential triggers, such as mechanical force, sublimation, electromagnetism. The conclusion discusses the fundamental value of systematic investigations of the structure-property relationships within these materials and opportunities for unlocking novel functionalities in future versions of adhesives.

Switchable Photonic Bio-Adhesive Materials

A soft photonic bio-adhesive material is designed with real-time colorimetrical monitoring of switchable adhesion by integrating a responsive bio-photonic matrix with mobile hydrogen-binding networking. Synergetic materials sequencing creates a unique iridescent appearance directly coupled with both adhesive ability and shearing strength, in a highly reversible manner. The responsive photonic materials, having a physically hydrogen-bonded chiral nematic organization, vary their adhesion strength due to a transition in cohesive and interfacial failure mechanism in humid surroundings. The bright color appearance shifts from blue to red to transparent and back due to a change in pitch length of the chiral helicoidal organization that also triggers coupled changes in both mechanical strength and interfacial adhesion. Such reversible strength-adhesion-iridescence triple-coupling phenomenon is further explored for design of super-strong switchable bio-adhesives for synthetic/biological surfaces with quick remotely triggered sticky-to-nonsticky transitions, removable conformal soft stickers, and wound dressings with visual monitoring of the healing process, to colorimetric stickers for contaminated respiratory masks.

Programmable Chromism and Photoluminescence of Spiropyran-Based Liquid Crystalline Polymer with Tunable Glass Transition Temperature

Spiropyran-based materials (SPBMs) can give responses to the stimulations induced by the light, heat, force, or pH, which have been used as triggers for many smart materials. Here, a cross-linkable SPBM containing mesogenic-units is synthesized, which is pale-colored, non-photoluminescent and non-mesogenic at a spiro form, but dark-colored, photoluminescent, and mesogenic at a merocyanine form. Moreover, the dynamic interconversion behavior of the form in the different chemical environments are distinct. Liquid crystalline polymers (LCPs) containing the SPBMs cross-linked via visible light, own a photoswitchable glass transition temperature (T_g ) and retain the switchable property; however, the SPBMs cross-linked via UV light will be locked at the MC state, because the molecular movement was frozen at the room temperature lower than the given T_g of the LCP. Thus, programmable chromism and photoluminescence based on the tunable T_g can be endowed to the functional materials prepared from the SPBMs.

A Superstrong and Reversible Ionic Crystal-Based Adhesive Inspired by Ice Adhesion

In this study, we developed a superstrong and reversible adhesive, which can possess a high bonding strength in the "adhesive" state and detach with the application of heating. An ionic crystal (IC) gel, in which an IC was immobilized within a soft-polymer matrix, were synthesized via in situ photo-crosslinking of a precursor solution composed of N, N-dimethyl acrylamide (DMAA) and a melted IC. The obtained IC gel is homogenous and transparent at melt point. When cooled to the phase transition temperature of the IC, the gel turns into the adhesive with the adhesion strength of 5.82 MPa (on glasses), due to the excellent wetting of melted gel and a thin layer of crystalline IC with high cohesive strength formed on the substrates. The synergistic effects between IC, polymer networks and substrates were investigated by solid state ¹ H NMR and molecular dynamics simulation. Such an adhesive layer is reversable and can be detached by heating and subsequent re-adhesion via cooling. This study proposed the new design of removable adhesives, which can be used in dynamic and complex environments.

Zwitterionic liquid crystalline polythiophene as an antibiofouling biomaterial

To address a key challenge of conjugated polymers in biomedical applications having poor antifouling properties that eventually leads to the failure and reduced lifetime of bioelectronics in the body, herein we describe the design, synthesis, and evaluation of our newly designed multifunctional zwitterionic liquid crystalline polymer PCBTh-C8C10, which is facilely synthesized using oxidative polymerization. A conjugated polythiophene backbone, a multifunctional zwitterionic side chain, and a mesogenic unit are integrated into one segment. By DSC and POM characterization, we verify that the introduction of 3,5-bis(2-octyl-1-dodecyloxy)benzene as a mesogenic unit into the polythiophene backbone allows the formation of the liquid crystalline mesophase of the resulting polymer. We also demonstrate that the PCBTh-C8C10 coated surface exhibits good conductivity, stability, hydrophilicity, and remarkable antibiofouling properties against protein adsorption, cell growth, and bacteria attachment. This new zwitterionic liquid crystalline polymer having good antibiofouling features will be widely recognized as a promising biomaterial that is applicable in implantable organic bioelectronics via inhibiting the foreign body response. A deep understanding of structure-property relationships of zwitterionic conjugated polymers has also been provided in this study.

[2,2](5,8)Picenophanedienes: Syntheses, Structural Analyses, Molecular Dynamics, and Reversible Intramolecular Structure Conversion

This study presents an important and efficient synthetic approach to 5,8-dibromo-2,11-di-tert-butylpicene (3), with multigram scale, which was then converted to a new series of picenophanes (6-10). The tub-shaped [2,2](5,8)picenophanediene 8 with two cis-ethylene linkers was explored using X-ray crystallography. The tub-to-tub inversion proceed through the successive bending of the linkers and the barrier for isopropyl-substituted derivative 10 was experimentally estimated to be 18.7 kcal/mol. Picenophanes with a large π-system and semi-rigid structure exhibited anomalous photophysical properties. The ethano-bridged picenophane shows the weak exciton delocalization while the cis-ethylene-bridged picenophane exhibits dual emission rendered by the weakly delocalized exciton and excimer. With the aid of the ultrafast time-resolved emission spectroscopy, the mechanism of the excimer formation is resolved, showing a unique behavior of two-state reversible reaction with fast structural deformation whose lifetime is around 20 ps at 298 K. This work demonstrates that the slight difference in the bridge of tub-shaped picenophanes renders distinct photophysical behavior, revealing the potential of harnessing inter-moiety reaction in the picenophane systems.

Flapping Peryleneimide as a Fluorogenic Dye with High Photostability and Strong Visible-Light Absorption

Flapping fluorophores (FLAP) with a flexible 8π ring are rapidly gaining attention as a versatile photofunctional system. Here we report a highly photostable "flapping peryleneimide" with an unprecedented fluorogenic mechanism based on a bent-to-planar conformational change in the S₁ excited state. The S₁ planarization induces an electronic configurational switch, almost quenching the inherent fluorescence (FL) of the peryleneimide moieties. However, the FL quantum yield is remarkably improved with a prolonged lifetime upon a slight environmental change. This fluorogenic function is realized by sensitive π-conjugation design, as a more π-expanded analogue does not show the planarization dynamics. With strong visible-light absorption, the FL lifetime response synchronized with the flexible flapping motion is useful for the latest optical techniques such as FL lifetime imaging microscopy (FLIM).

Laser-induced formation of "craters" and "hills" in azobenzene-containing polymethacrylate films

Functional organic polymer materials with an ability to change their surface topography in response to external contactless stimuli, like light irradiation, have attracted considerable attention. This work is devoted to the study of contactless control of the surface topography and the formation of the surface features in the amorphousized and liquid crystalline films of two azobenzene-containing polymers. The investigated polymers are side-chain polymethacrylates containing azobenzene chromophores with two lateral methyl substituents in ortho-positions and differing in the length of flexible spacer with six and ten methylene units. Two lateral methyl substituents at the azobenzene chromophore ensure high photoresponses of these polymeric samples in the whole visible spectral range. Irradiation of the polymethacrylate films by focused polarized light of green (532 nm) and red (633 nm) lasers induces a specific photodeformation of the film surface. In the case of the green light formation of circular "craters" with anisotropic borders was found, whereas for the red light highly asymmetric "hills" were observed. The possible mechanisms of the surface topography formation and their features are discussed.

Recent Progress in High Linearly Fused Polycyclic Conjugated Hydrocarbons (PCHs, n > 6) with Well-Defined Structures

Although polycyclic conjugated hydrocarbons (PCHs) and their analogues have gained great progress in the fields of organic photoelectronic materials, the in-depth study on present PCHs is still limited to hexacene or below because longer PCHs are insoluble, unstable, and tediously synthesized. Very recently, various strategies including on-surface synthesis are developed to address these issues and many higher novel PCHs are constructed. Therefore, it is necessary to review these advances. Here, the recent synthetic approach, basic physicochemical properties, single-crystal packing behaviors, and potential applications of the linearly fused PCHs (higher than hexacene), including acenes or π-extended acenes with fused six-membered benzenoid rings and other four-membered, five-membered or even seven-membered and eight-membered fused compounds, are summarized.

How an Eight-Membered Ring Alters the Rhodamine Chromophore

Readily available phenylene-1,3-diamines can be converted into unprecedented analogues of rhodamine and malachite green possessing a central eight-membered ring in three steps. The overall process couples a cyanine chromophore with a urea bridge giving rise to new dyes possessing distinct spectral characteristics: absorption of orange light combined with a weak emission of red light both in solution and in the crystalline state. Their photophysics is governed by the twist of lateral phenyl rings and intramolecular and intermolecular CT transitions.

Reversible Adhesion via Light-Regulated Conformations of Rubber Chains

Bio-inspired reversible adhesives have attracted great attention because of their promising applications in the electronic, biomedical, and robotic fields. Here, to achieve in situ reversible adhesion, a new concept is demonstrated by modulating the conformations of polydimethylsiloxane (PDMS) chains. The new adhesive, termed B_GP_P, is composed of the graphene/PDMS composite (GP) as the backing layer and PDMS as the micropillar array. The photothermal effect of graphene under UV irradiation heats up the micropillars, resulting in an increase in the chain conformations of PDMS and thus the contact points with the counterpart surface. The more contact points together with the alignment of PDMS chains during the shearing result in an adhesion much higher than that without UV irradiation. The adhesion switching thus does not rely on the changing of the contact area, and so the macroscopic deformation of structures is avoided. The results suggest a new design principle for light-controllable structured adhesive, which could be conceptualized into other rubbery materials.

Inference-assisted intelligent crystallography based on preliminary data

Crystal structure analysis is routinely used to determine atomically resolved molecular structures and structure-property relationships. The accumulation of reliable structural characteristics obtained by crystal structure analysis has forged a robust basis that is frequently used in molecular and materials sciences. However, experimental techniques remain hampered by time-consuming ‘blind’ measurement-analysis iterations, which are sometimes required to find appropriate crystals and experimental conditions. Herein, we present a method that uses a small preliminary data set to evaluate the to-be-observed structures and the to-be-collected data. Moreover, we demonstrate the practical utility of this method to improve the efficiency of crystal structure analysis. This method will help selecting suitable crystals and choosing favorable experimental conditions to generate results that satisfy the level of precision required for specific research objectives.

Light-Switchable Polymer Adhesive Based on Photoinduced Reversible Solid-to-Liquid Transitions

The development of switchable adhesives for reversible bonding and debonding can overcome the problems associated with conventional adhesives in separating, recycling, and repairing glued surfaces. Here, a photoresponsive azobenzene-containing polymer (azopolymer) is developed for photocontrolled adhesion. The azopolymer P1 (poly(6-(4-(p-tolyldiazenyl)phenoxy)hexyl acrylate)) exhibits photoinduced reversible solid-to-liquid transitions due to trans-cis photoisomerization. Trans P1 is a solid that glues two substrates with a stiffness comparable to that of conventional adhesives. UV light induces trans-to-cis isomerization, liquefies P1, weakens the adhesion, and facilitates the separation of glued substrates. Conversely, visible light induces cis-to-trans isomerization, solidifies P1, and enhances the adhesion. P1 enables photocontrolled reversible adhesion for various substrates with different wettability, chemical compositions, and surface roughness. P1 can also be implemented in both dry and wet environments. Light can control the adhesion process with high spatiotemporal resolution when using P1 as a switchable adhesive. Photoinduced reversible solid-to-liquid transitions represent a strategy for materials recycling and automated production processes that require reversible bonding and debonding.

Monitoring Fluorescence Response of Amphiphilic Flapping Molecules in Compressed Monolayers at the Air-Water Interface

The air-water interface, which is the boundary of two phases with a large difference in polarity, gives a distinct environment compared with bulk water or air. Since the interface provides a field for various biomolecules to work, it is important to understand the molecular behaviors at the interface. Here, polarity-independent flapping viscosity probes (FLAP) equipped with hydrophobic/hydrophilic substituents have been synthesized and studied at the air-water interface. In situ fluorescence (FL), which is related to the internal motion and orientation, of three different FLAPs were investigated at the interface, and the internal motion of the molecule was indicated to be suppressed at the interface. In addition, the molecular response was compared with that of conventional viscosity probes (molecular rotors), which indicates the different behaviors of FLAP probably due to the distinct molecular orientation as well as molecular motion.