Side Groups Research Articles

Design and synthesis of low‐dieclectric polyaryl ethers containing bulky tetraphenyl vinyl pendant group

AbstractA tetraphenylethylene‐containing bisphenol monomer 5‐[4‐(triphenylvinyl)phenyl]benzene‐1,3‐diol (TPE‐OH) was designed and synthesized by Suzuki coupling and nucleophilic substitution reaction. By adjusting the proportion of TPE‐OH, a series of rigid polyaryl ether, namely PPTES, were facilely synthesized by homopolymerization or copolymerization with 4‐(4‐hydroxyphenyl)‐2,3‐diazepine‐1‐one (DHPZ) and 4,4′‐difluorodiphenyl sulfone (DFS). The following characterization of their structures with nuclear magnetic resonance and infrared spectroscopy confirmed successful synthesis of both monomers and polymers. Large, volume‐twisted and non‐coplanar rigid tetraphenylethylene could effectively increase the molecular chain spacing and reduce the regularity of the molecular chain, as evidenced by molecular dynamics simulation with Materials Studio, in turn to form an amorphous nature of PPTES phase state. In addition, such PPTESs have excellent solubility, heat resistance, and other comprehensive properties. Their glass transition temperature (Tg) is between 219 and 300°C, and the 5% thermogravimetric temperature of PPTESs locates at 490–539°C under N2 atmosphere. At 1 GHz, the intrinsic dielectric permittivity of polymer films is between 2.32 and 2.61, gradually decreases with TPE‐OH content. This work would provide new idea and choice for the selection of polyaryl ether resin bisphenol monomer, and promote the development and application of low‐dielectric polyarylether materials.

Synthesis of colorless polyimides derived from benzimidazole diamines with bis‐amide structures

AbstractTo make the colorless polyimides (CPIs) suitable for the application of flexible display technology, the polyimide (PI) films need to have both good optical properties and thermal properties. To get the wanted properties, 2‐(2‐methyl‐4‐(2‐methyl‐4‐aminobenzamido)phenyl)‐5‐(2‐methyl‐4‐aminobenzamido)‐N‐phenylbenzimidazol (5a) and 2‐(2‐methyl‐4‐(2‐trifluoromethyl‐4‐aminobenzamido)phenyl)‐5‐(2‐trifluoromethyl‐4‐aminobenzamido)‐N‐phenylbenzimidazol (5b) were synthesized, which both contained benzimidazole and bis‐amide structures. Two kinds of PI films were polymerized with cyclobutane‐1,2,3,4‐tetracarboxylic dianhydride (CBDA). With the contribution of side groups (CH3 or CF3), the resulting PI films presented relatively superior optical properties (transmittance at 400 nm was 59% and 68% respectively) and low coefficient of thermal expansion (CTE = 22 and 25 ppm K−1). These good properties suggest that these PI films have the potential for flexible display usage.

High conductive and dimensional stability proton exchange membranes with an all-carbon main chain and densely sulfonated structure

Sulfonated polyarylene membranes are demonstrated to be efficient as proton exchange membranes (PEMs) for proton exchange membrane fuel cells (PEMFCs) in clean energy conversion systems. In this study, we design and synthesize a series of sulfonated polyarylene with all-carbon backbones and densely sulfonated pendant groups, which can be prepared by copolymerization of 1,3-Disulfonic acid benzaldehyde, 1,1,1-trifluoroacetone and biphenyl under superacid-catalyzed conditions. Rigid, hydrophobic backbone and hydrophilic side chains make the membrane form good microphase separation morphology. The PEMs exhibit high proton conductivity (404 mS cm−1) and excellent dimensional stability (swelling ratio lower than 24% and water uptake lower than 40%) at 80 °C. Moreover, the PEMs show good oxidization stability (the retaining weight rate of membrane up to 99.2% for 1 h oxidative treatment), and the oxidization stability and degradation mechanism of Ar3CH in polymer backbone are also studied. The H2/O2 fuel cell assembled with PEMs exhibited a maximum peak power density of 560 mW cm−2. It indicates that all-carbon main chain and densely sulfonated structure show great potential for improving the performance of PEMs.

Ionic hyper-cross-linked porous polymer networks with achiral and chiral pyridinium-type segments

A new type of ionic porous polymer networks (PPNs) is reported containing (i) N-alkyl pyridinium bromide ionic groups and (ii) a hyper-cross-linked scaffold based on polyacetylene (polyene) chains the rigidity of which contributes to the permanent porosity the PPNs. The ionic PPNs were prepared by a combination of chain-growth polymerization of acetylenic monomers and quaternization reactions of pyridine and alkyl bromide moieties. The wide variability of this synthetic concept enabled the preparation of covalently diverse PPNs with ionic groups located either in the pendant groups or in the knots of the networks, as well as the preparation of PPNs with chiral ionic groups. The content of ionic groups in PPNs ranged from 1.5 to 4.2 mmol/g, and the BET area was from 67 to 744 m2/g. The mode of quaternization used (prepolymerization or postpolymerization) controlled the contribution of micropores and mesopores to the porosity of the ionic PPNs. The polyacetylene ionic PPNs were active as heterogeneous organocatalysts (applied without a cocatalyst) for the cycloaddition of CO2 to styrene oxide yielding styrene carbonate as the only product (up to 96 %). PPNs with chiral ionic groups showed potential for enantioselective catalysis of this reaction. The catalytic activity was controlled by the accessibility of pyridinium active centres for the substrate molecules. Ionic PPNs prepared were also efficient in reversible water vapour capturing and releasing (capacity up to 361 mg/g at 298 K and RH = 90 %). Both surface adsorption and capillary condensation of H2O contributed to the water vapour capture on reported PPNs.

Combining Cyclic Units and Unsaturated Pendant Groups by Propene/1,5-Hexadiene Copolymerization Toward Functional Isotactic Polypropylene.

The precise use of a widely available and inexpensive metallocene catalyst enabled the synthesis of isotactic polypropylene copolymers characterized by the copresence of randomly distributed cyclic units in the backbone and unsaturated pendant units employing 1,5-hexadiene as comonomer. Optimization of the polymerization conditions avoided the cross-linking phenomena that negatively affects the material processing and final properties, resulting in good yields of samples featuring high molecular masses and a precisely controlled microstructure. Such polypropylene-based copolymers exhibit a broad spectrum of properties ranging from thermoplastic to surprising elastomeric behavior, with the additional value of being functionalizable by post-polymerization reactions.

Seamless, Self-Transformation of Thermoplastic Polyesters into Vitrimers Through Bond Exchange-Triggered Cross-Linking.

In this study, a seamless, self-transformation system of linear thermoplastic polyesters into the sustainable cross-linked polymers, vitrimers, is demonstrated. The key is the use of polyesters bearing abundant hydroxyl side groups, which are synthesized via the reaction using dithiol molecules bearing ester units and diepoxy molecules. The polymerization reaction progresses efficiently at relatively low temperature due to the click nature of the thiol-epoxy reaction, which provides the hydroxyl side groups along the polyester chain. The tin catalyst (stannous octoate) is added in the initial polymerization, and the catalyst also works to cross-link the polyesters via intermolecular transesterification bond exchange simply by heating at high temperatures. By adjusting the degrees of cross-linking, the mechanical properties as well as the thermal properties are well tuned. The bond exchange can still be activated in the final cross-linked sample; and thus, the material behaves as vitrimers, exhibiting mechanical recyclability. The application of a new type of hot melt adhesive, where the post-coating tuning/enhancement of adhesion strength is realized, is also demonstrated. On the whole, the present system is very simple but proposes a new application window of bond exchange concept into self-transformation polymers.

Vitamin B3 Containing Polymers for Nanodelivery.

Polymeric nanoparticles (NPs) with an integrated dual delivery system enable the controlled release of bioactive molecules and drugs, providingtherapeutic advantages. Key design targets include high biocompatibility, cellular uptake, and encapsulating efficiency. In this study, a polymer library derived from niacin, also known as vitamin B3 is synthesized. The library comprises poly(2-(acryloyloxy)ethyl nicotinate) (PAEN), poly(2-acrylamidoethyl nicotinate) (PAAEN), and poly(N-(2-acrylamidoethyl)nicotinamide) (PAAENA), with varying hydrophilicity in the backbone and pendant group linker. All polymers are formulated, and those with increased hydrophobicity yield NPs with homogeneous spherical distribution and diameters below 150 nm, as confirmed by scanning electron microscopy and dynamic light scattering. Encapsulation studies utilizing a model drug, neutral lipid orange (NLO), reveal the influence of polymer backbone on encapsulation efficiency. Specifically, efficiencies of 46% and 96% are observed with acrylate and acrylamide backbones, respectively. Biological investigations showed that P(AEN) and P(AAEN) NPs are non-toxic up to 300µg mL-1, exhibit superior cellular uptake, and boost cell metabolic activity. The latter is attributed to the cellular release of niacin, a precursor to nicotinamide adenine dinucleotide (NAD), a central coenzyme in metabolism. The results underline the potential of nutrient-derived polymers as pro-nutrient and drug-delivery materials.

Hydrogen-bonded cytosine-endowed supramolecular polymeric nanogels: Highly efficient cancer cell targeting and enhanced therapeutic efficacy

We demonstrate that cytosine moieties within physically cross-linked supramolecular polymers not only manipulate drug delivery and release, but also confer specific targeting of cancer cells to effectively enhance the safety and efficacy of chemotherapy—and thus hold significant potential as a new perspective for development of drug delivery systems. Herein, we successfully developed physically cross-linked supramolecular polymers (PECH-PEG-Cy) comprised of hydrogen-bonding cytosine pendant groups, hydrophilic poly(ethylene glycol) side chains, and a hydrophobic poly(epichlorohydrin) main chain. The polymers spontaneously self-assemble into a reversibly hydrogen-bonded network structure induced by cytosine and directly form spherical nanogels in aqueous solution. Nanogels with a high hydrogen-bond network density (i.e., a higher content of cytosine moieties) exhibit outstanding long-term structural stability in cell culture substrates containing serum, whereas nanogels with a relatively low hydrogen-bond network density cannot preserve their structural integrity. The nanogels also exhibit numerous unique physicochemical characteristics in aqueous solution, such as a desirable spherical size, high biocompatibility with normal and cancer cells, excellent drug encapsulation capacity, and controlled pH-responsive drug release properties. More importantly, in vitro experiments conclusively indicate the drug-loaded PECH-PEG-Cy nanogels can selectively induce cancer cell-specific apoptosis and cell death via cytosine receptor-mediated endocytosis, without significantly harming normal cells. In contrast, control drug-loaded PECH-PEG nanogels, which lack cytosine moieties in their structure, can only induce cell death in cancer cells through non-specific pathways, which significantly inhibits the induction of apoptosis. This work clearly demonstrates that the cytosine moieties in PECH-PEG-Cy nanogels confer selective affinity for the surface of cancer cells, which enhances their targeted cellular uptake, cytotoxicity, and subsequent induction of programmed cell death in cancer cells.

Meta-aramid film with both flexibility and strength: Combined effect of aromatic ether bond and micro-branched structure

Developing Meta-aramid materials that combine flexibility and strength will greatly expand their application fields. In previous work, it was demonstrated that aromatic ether bonds can contribute to improving flexibility. In addition, micro-branched chain structures can reduce intermolecular forces by increasing fractional free volume, while newly formed hydrogen bonding can maintain polymer strength. Therefore, two flexible polymers were obtained by incorporating 4,4′-diaminodiphenyl ether (ODA) and 4,4′-oxybis [3-(trifluoromethyl)benzenamine] (OTB) to the molecular chains, respectively, and flexible films were prepared by a combination of solution casting and dry-wet processing methods. By studying the properties of copolymer films with 10% ODA and 10% OTB added, it was found that they can maintain thermal stability and mechanical strength while improving the flexibility of the films. The AFM results visually showed that the DMT modulus of the modified films decreased at the micro level and DMA indicated that the introduction of ODA and OTB can shorten the molecular relaxation time, which reflected the improvement of molecular chain flexibility. Through molecular dynamics simulations, the differences were compared in molecular chain conformation, mean square displacement and hydrogen bonding after the introduction of ODA and OTB and the combined mechanism of aromatic ether bonds and CF3 side groups was confirmed in improving flexibility and maintaining mechanical strength.

Topology-Accelerated and Selective Cascade Depolymerization of Architecturally Complex Polyesters.

Despite considerable recent advances already made in developing chemically circular polymers (CPs), the current framework predominantly focuses on CPs with linear-chain structures of different monomer types. As polymer properties are determined by not only composition but also topology, manipulating the topology of the single-monomer-based CP systems from linear-chain structures to architecturally complex polymers could potentially modulate the resulting polymer properties without changing the chemical composition, thereby advancing the concept of monomaterial product design. To that end, here, we introduce a chemically circular hyperbranched polyester (HBPE), synthesized by a mixed chain-growth and step-growth polymerization of a rationally designed bicyclic lactone with a pendent hydroxyl group (BiLOH). This HBPE exhibits full chemical recyclability despite its architectural complexity, showing quantitative selectivity for regeneration of BiLOH, via a unique cascade depolymerization mechanism. Moreover, distinct differences in materials properties and performance arising from topological variations between HBPE, hb-PBiLOH, and its linear analogue, l-PBiLOH, have been revealed where generally the branched structure led to more favorable interchain interactions, and topology-amplified optical activity has also been observed for chiral (1S, 4S, 5S)-hb-PBiLOH. More intriguingly, depolymerization of l-PBiLOH proceeds through an unexpected, initial topological transformation to the HBPE polymer, followed by the faster cascade depolymerization pathway adopted by hb-PBiLOH. Overall, these results demonstrate that CP design can go beyond typical linear polymers, and rationally redesigned, architecturally complex polymers for their unique properties may synergistically impart advantages in topology-augmented depolymerization acceleration and selectivity for exclusive monomer regeneration.

Spiro[fluorene-9,9′-xanthene]-based hole transporting materials modulated by mono- and bis- benzodioxino[2,3-b]pyrazine pendant groups for perovskite QLEDs

In this work, we designed and synthesized two new hole-transporting materials with a nonplanar three-dimensional (3D) conformation. They were achieved by incorporating spiro[fluorene-9,9′-xanthene] as a cross-shaped configuration scaffold and adding either mono- (H1) or bis- benzodioxino[2,3-b]pyrazine (H2) pyrazine as pendant groups. Both compounds exhibit remarkable thermal stability, with thermal decomposition temperature (Td) of 462 (H1) and 504 °C (H2), respectively. Moreover, the structural substitution with benzodioxino[2,3-b]pyrazine units successfully aligned the energy levels of both materials with the perovskite quantum dot luminescence layer. Hereby, the fabricated perovskite QLEDs using H1 as hole-transporting materials (HTMs) featured an excellent average external quantum efficiency (EQE) of up to 9.5% with a maximum luminance of 22368 cd m−2, which is much higher than that of the H2-based devices with an EQE of 6.6% under the same conditions. The excellent device performance from H1 can be attributed to its asymmetric structure by the introduction of monosubstituted benzodioxino[2,3-b]pyrazine groups, as evidenced by its high hole mobility of 1.90 × 10−4 cm2 V−1 s−1 and improved interface interaction with adjunct layers. Thus, this design approach may bring a fresh perspective to the utilization of solution-processable small-molecule HTMs in high-performance Pe-QLEDs and other optoelectronics in the future.

Chemical Structure-Physicochemical Property Relationships of Copolymers Utilizable for Negative-Tone Photoimaging via Chemical Amplification.

We demonstrate an understanding of different physicochemical properties of copolymers induced by systematic changes in their structural parameters, i.e., the chemical structure of the comonomer unit, composition, molecular weight, and dispersity. The terpolymers were designed to be implemented in a chemically amplified resist (CAR) to form negative-tone patterns. With two basic repeating units of 4-hydroxystyrene and 2-ethyl-2-methacryloxyadamantane as monomers for conventional CARs, the pendant group of the third methacrylate comonomer was varied from aromatic, aliphatic lactone to lactone rings to modulate the interaction capability of the copolymer chains with n-butyl acetate, which is a negative-tone developer. Along with these structures, the monomer composition, molecular weight, and dispersity were also controlled. Physicochemical properties of the synthesized copolymers having controlled structures, i.e., dissolution behaviors and quantified Hansen solubility parameters, surface wetting characteristics, and surface roughness, which can be important properties affecting patterning capability in high-resolution lithography, were explored. Furthermore, the feasibility to use experimentally determined Hansen solubility parameters of the copolymers for the prediction of pattern formation using a coarse-grained model was assessed. Our comprehensive studies on the correlation of the structural parameters of the copolymers with final properties offer fundamental avenues to attain effective designs of the complex CAR system toward the lithographic process to achieve a sub-10 nm dimension, which is close to a single-chain dimension.

Backbone and Side Group Interchain Correlations Govern Wide-Angle X-ray Scattering of Poly(3-hexylthiophene).

Identifying the origin of scattering from polymer materials is crucial to infer structural features that can relate to functional properties. Here, we use our recently developed virtual-site coarse graining to accelerate atomistic simulations and show how various molecular features govern wide-angle X-ray scattering from a conjugated polymer, poly(3-hexylthiophene) (P3HT). The efficient molecular dynamics simulations can represent the structure and capture the emergence of crystalline order from amorphous melts upon cooling while retaining atomistic details of chain configurations. The scattering extracted from simulations shows good agreement with wide-angle X-ray scattering experiments. Amorphous P3HT exhibits broad scattering peaks: a high-q peak from interchain side-group correlations and a low-q peak from interchain backbone-backbone correlations. During amorphous to crystalline phase transitions, the distance between backbones along the side-group direction increases because of lack of interdigitation in the crystalline phase. Scattering from π-π stacking emerges only after crystallization takes place. Intrachain correlations contribute negligibly to the scattering from the amorphous and crystalline phases.

The Electron-Rich and Nucleophilic N-Heterocyclic Imines on Metal Surfaces: Binding Modes and Interfacial Charge Transfer.

The strongly electron-donating N-heterocyclic imines (NHIs) have been employed as excellent surface anchors for the thermodynamic stabilization of electron-deficient species due to their enhanced nucleophilicity. However, the binding mode and interfacial property of these new ligands are still unclear, representing a bottleneck for advanced applications in surface functionalization and catalysis. Here, NHIs with different side groups have been rationally designed, synthesized, and analyzed on various metal surfaces (Cu, Ag). Our results reveal different binding modes depending on the molecular structure and metal surface. The molecular design enables us to achieve a flat-lying or upright configuration and even a transition between these two binding modes depending on the coverage and time. Importantly, the two binding modes exhibit different degrees of interfacial charge transfer between the molecule and the surface. This study provides essential microscopic insight into the NHI adsorption geometry and interfacial charge transfer for the optimization of heterogeneous catalysts in coordination chemistry.

Polymerizable rotaxane of cucurbituril protecting dopamine based adhesive hydrogels

The catechol moiety found within mussel proteins plays a pivotal role in enhancing their adhesive properties. Nonetheless, catechol compounds, such as dopamine (DOP) derivatives, are susceptible to oxidation, leading to the formation of quinone. This oxidation process poses a significant challenge in the development of DOP-based hydrogels, hampering their adhesion capabilities and hindering polymerization. To protect DOP moieties from oxidation, DOP and N-(3-aminopropyl)methacrylamide (AMA) moieties were grafted onto the side groups of biocompatible poly(glutamic acid) (PGA). Subsequently, the DOP unit, serving as a second guest, would be captured by a polymerizable rotaxane of cucurbituril (CB[n]), in which the host molecule CB[8] complexed with the first guest, polymerizable methyl viologen (MV), forming a protective function and dynamic cross-linking. Upon exposure to light curing, a composite network emerged through the synergy of covalent cross-linking and supramolecular host-guest complexation of DOP with CB[8]. The generated complexation between DOP and CB[8] could protect the DOP moieties, resulting in photocured hydrogels with exceptional adhesive strength and remarkable tensile capabilities. Moreover, 3D printing technology was used to create various models with these DOP-based hydrogels, demonstrating their promising applications in future.

Synthesis and properties of novel poly(ester-amide-imide)s containing pendant phthalimide substituents

Two series of novel poly(ester-amide-imide)s (PEsAIs) with pendant phthalimide side group were synthesized by copolymerization of phthalimide-hydroquinone bis(trimellitate anhydride) (PI-TAHQ), p-phthaloyl chloride (TPC) and other fluorinated monomers using the two-step method. These PEsAIs had glass transition temperatures ( Tgs) in the range of 228 °C–296°C and coefficients of thermal expansion (CTEs) of 18–55 ppm·K−1. These films had good mechanical properties with tensile modulus of 3.7–5.7 GPa, tensile strengths of 92–153 MPa and elongations at break of 2.2%–8.3%. All films displayed good transparency with transmittances at 400 nm (T400nm) of 43%–79% and transmittances at 850 nm (T850nm) exceeding 89%, and these PEsAIs were amorphous. Especially, PEsAI-d-60 presented the best comprehensive performance with Tg of 296°C, low CTE of 18 ppm·K−1 and high transmittance (T400nm of 79%, T850nm of 91%), which exhibited the potential of this novel poly(ester-amide-imide) containing pendant phthalimide substituent in optical transparent materials.

Synthetic Polypeptide Bioadhesive Based on Cation-π Interaction and Secondary Structure.

Bioadhesives have garnered widespread attention in the biomedical field, for wound healing and tissue sealing. However, challenges exist due to the inferior performance of bioadhesives, including weak adhesion, poor biocompatibility, or lack of biodegradability. In this work, we demonstrate the fabrication of hydrogel adhesive based on polypeptides composed of lysine and glutamic acid. The cation-π interaction between the ammonium cations and phenyl groups endows the hydrogel with strong cohesion, and the hydrophobicity of the phenyl group significantly enhances the interaction between polypeptides and the substrate interface, leading to excellent adhesive performance. The equivalent molar ratio of ammonium cations and the phenyl group is beneficial for the enhancement of adhesiveness. Furthermore, we discover that the polypeptides with an α-helix exhibit better adhesiveness than the polypeptides with a β-sheet because the α-helical structure can increase the exposure of the side group on the polypeptide surface, which further strengthens the interaction between polypeptides and the substrate. Besides, this synthetic polypeptide adhesive can seal the tissue quickly and remain intact in water. This adhesive holds significant promise for application in wound healing and tissue sealing, and this study provides insight into the development of more peptide-based adhesives.

Linearly-Changed Thermal Behavior and Depressed Brill Transition in Long-Chain Polyamides Substituted by Methyl Side Groups.

Side substitution is an effective way of functionalizing and modifying the properties of polyamides. Meanwhile, side substitution would significantly influence the crystallization kinetics and polymorphic phase transition of polyamides, which, however, has not been well elucidated. Herein, we synthesized the side-substituted long-chain polyamides with various content of methyl pendent groups and investigated their crystallization and phase transition behaviors. We find that the thermal parameters of side-substituted polyamides vary linearly with the side group content, analogous to the isomorphic crystallization of random copolymers. All the solution-crystallized polyamides experience the α-γ Brill transition during heating, with the Brill transition temperature linearly decreasing as the side group content increases. Intriguingly, the γ-α transition of polyamides during cooling is suppressed with the presence of side methyl groups due to the difficulty in H-bond reorganization and gauche-trans conformational changes. This work has demonstrated the critical role of side substitution in the polymorphic crystallization and phase transition of long-chain polyamides.

Sustainable ultra-strong polyesteramide elastomers with rapid degradation and high resilience

Degradable polymers typically require prolonged exposure to harsh conditions for degradation, but this extended duration and severe treatment often result in incomplete breakdown, leading to the formation of harmful microplastics that pose significant environmental pollution risks. In this work, degradable alternating polyamide hard segments and soft crystallizable segments were combined by amide groups to design thermoplastic bio-based polyesteramide elastomers (PEAEs) with customizable properties and rapid degradability. The hard segment of the polymer features an alternating arrangement of amide and ester bonds. This arrangement facilitates the formation of small molecule monomers when the ester bond is broken, preventing microplastic contamination that may arise from incomplete degradation of the hard segment. Additionally, the inclusion of side groups in the soft segment disrupts the crystallization, enhancing its susceptibility to solvent penetration and thereby accelerating the degradation rate. After step-cyclic tensile tests, additional physical cross-linking points were formed in PEAEs to enhance their mechanical strength and elasticity. Furthermore, PEAEs demonstrated outstanding processing capabilities, including compounding, extrusion, pelletization, and spinning. This innovative approach introduces fresh design concepts for the industrial application of bio-based degradable polymers, playing a pivotal role in advancing resource conservation and environmental protection.

Azobenzene isomerization on a reactive copper surface by efficient decoupling with bulky side groups

Azobenzene derivatives, an important class of molecular switches that undergo isomerization between trans and cis states, have been studied on various coinage metal surfaces in the past. However, on reactive copper surfaces switching turned out to be difficult. Here, we show that the use of bulky 2,6-dimethylphenyl side groups enables switching on a Cu(111) surface as studied by scanning tunneling microscopy. By applying voltage pulses from the STM tip, irreversible trans → cis isomerization of individual molecules can be induced where exactly one molecule within each unit cell is isomerized. The absence of backward cis → trans switching illustrates the importance of the adsorption structure on the potential energy landscape of azobenzene. Isomerization, which is activated by inelastic scattering of single tunneling electrons, happens in a very localized fashion, thus allowing to ‘write’ patterns of individual cis isomers into the homogeneous molecular layer. Our study demonstrates how the bulky spacer groups direct adsorption and self-assembly into close-packed structures, which are similar to three-dimensional molecular crystals, on the surface. In addition, they modulate the electronic coupling to the underlying substrate to maintain successful switching behavior even on the most reactive coinage metal surfaces.