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A combination of chalcogen bonds, one type of emerging non-covalent bonding force, and imine bonds, allow the control of the dynamic covalent chemistry with orbital interactions and the reversal of kinetic and thermodynamic selectivity.

A combination of diphenylethene and dynamic covalent chemistry for the modulation of reactivity and luminescence, stimuli-responsive multistate emission, and mechanochemical reactions in the solid state.

The manipulation of covalent bonds could be directed toward degradable, recyclable, and sustainable materials. However, there is an intrinsic conflict between properties of stability and degradability. Here we report light-controlled formation/scission of three types of covalent bonds (C-N, C-O, and C-S) through photoswitching between equilibrium and nonequilibrium states of dynamic covalent systems, achieving dual benefits of photoaddressable stability and cleavability. The photocyclization of dithienylethene fused aldehyde ring-chain tautomers turns on the reactivity, incorporating/releasing amines, alcohols, and thiols reversibly with high efficiency, respectively. Upon photocycloreversion the system is shifted to kinetically locked out-of-equilibrium form, enabling remarkable robustness of covalent assemblies. Reaction coupling allows remote and directional control of a diverse range of equilibria and further broadens the scope. Through locking and unlocking covalent linkages with light when needed, the utility is demonstrated with capture/release of bioactive molecules, modification of surfaces, and creation of polymers exhibiting tailored stability and degradability/recyclability. The versatile toolbox for photoswitchable dynamic covalent reactions to toggle matters on and off should be appealing to many endeavors.

The bidirectional interconversion between ketone and enol structures of 4-cyclopentene-1,3-dione derivatives was realized by photoswitching of fused dithienylethene using UV and visible light. A loss of antiaromaticity offered the driving force for light-triggered enolization and was supported by theoretical studies. Solvent and substituent effects provided additional means for regulating photoswitchable keto-enol tautomerism. Moreover, a significant change of acidity was revealed with light-induced keto-to-enol conversion, enabling control over base-catalyzed Michael addition.

Urea groups play an important role in organic, supramolecular, and materials chemistry owing to unique structural and molecular recognition features. Herein a strategy of reversible covalent bond constrained ureas was developed toward multi-addressable switchable luminescent molecules and materials. The combination of ortho urea and aldehyde led to equilibrating cyclic hemiaminals, and the fluorescence response can be tuned through multimodes, including acid, base, anion, temperature, and nucleophiles. Moreover, mechanism studies revealed the critical role of an emissive aromatic acyliminium ion intermediate in acidic media, enabling triple-state ON–OFF–ON switching by changing pH. Through controlling the dynamic system thermally activated fluorescence and tunable dynamic covalent reactions with nucleophiles were further achieved. The unique reactivity of the acyliminium ion intermediate also allowed the creation of proton relay mediated signaling cascades toward the regulation of fluorescence outputs. To demonstrate the utility multi-stimuli luminescence switching and the detection of various vapors were realized in the solid state. The current platform provides a new pathway for manipulating urea bonds and should be appealing to future research of assembly, sensing, and labelling.

The imine bond holds a prominent place in supramolecular chemistry and materials science, and one issue is the stability of imines due to their electrophilic nature. Here we introduced ortho-carboxylate groups into a series of aromatic aldehydes/imines for dictating imine dynamic covalent chemistry (DCC) through n → π* interactions, one class of widespread and yet underused non-covalent interactions. The thermodynamically stabilizing role of carboxylate-aldehyde/imine n → π* interactions in acetonitrile was elucidated by the movement of the imine exchange equilibrium and further supported by crystal analysis. Computational studies provided mechanistic insights for n → π* interactions, the strength of which can surpass that of CH hydrogen bonding and is dependent on the orientation of interacting sites based on natural bond orbital analysis. Moreover, the substituent effect and the combination of recognition sites allowed additional means for modulation. Finally, to show the relevance of our findings ortho-carboxylate containing aldehydes were used to regulate imine formation/exchange in water, and modification of the N-terminus of amino acids and peptides was achieved in a neutral buffer. This work represents the latest example of weak interactions governing DCC and sets the stage for assembly and application studies., A versatile strategy of n → π* interactions was developed for tunable control of dynamic imine chemistry and the regulation of imine formation/exchange in water.

A strategy of dynamic covalent chemistry within constrained biaryls was developed for the modulation of axial chirality. The ring fusion partners of amide and aldehyde allowed the manipulation of ring/chain equilibrium and chirality transfer within cyclic diastereomeric hemiaminal. Dynamic covalent reactions (DCRs) with alcohols, thiols, and secondary amines further enabled the reversal of chirality relay and thereby regulation of axial chirality. Moreover, a combination of NMR, X-ray, and density functional theory results shed light on the structural basis of chirality transfer, exhibiting modest to excellent diastereoselectivity under thermodynamic control. The critical role of the amide unit in the modulation of axial chirality was also corroborated. Finally, the chiroptical signal was controlled through changing solvents, DCRs, and stimuli-responsive switching of DCRs.

Orbital donor-acceptor interactions play critical roles throughout chemistry, and hence, their regulation and functionalization are of great significance. Herein we demonstrate for the first time the investigation of n→π* interactions through the strategy of dynamic covalent chemistry (DCC), and we further showcase its use in the stabilization of imine. The n→π* interaction between donor X and acceptor aldehyde/imine within 2-X-2'-formylbiphenyl derivatives was found to significantly influence the thermodynamics of imine exchange. The orbital interaction was then quantified through imine exchange, the equilibrium of which was successfully correlated with the difference in natural bond orbital stabilization energy of n→π* interactions of aldehyde and its imine. Moreover, the examination of solvent effects provided insights into the distinct feature of the modulation of n→π* interaction with aprotic and protic solvents. The n→π* interaction involving imine was enhanced in protic solvents due to hydrogen bonding with the solvent. This finding further enabled the stabilization of imine in purely aqueous solution. The strategies and results reported should find application in many fields, including molecular recognition, biological labeling, and asymmetric catalysis.

The role of n → π* orbital interactions in the rotational pathway and barrier of biaryl-based molecular rotors was elucidated through a combined experimental and computational study. The n → π* interaction in the transition state can lead to the acceleration of rotors. The competition between the n → π* interaction and hydrogen bonding further enabled the reversal of the pathway and greasing/braking the rotor in response to acid/base stimuli, thereby creating a switchable molecular rotor.

We report the development of multiresponsive thermally sensitive polymers through both supramolecular and reversible covalent strategies as well as their use in controlled encapsulation and release. Novel acylhydrazone-based dynamic covalent polymers displaying lower critical solution temperature (LCST) or upper critical solution temperature (UCST) were synthesized. A remarkable control over thermal phase transition can be tuned through multimodes, such as anions, cations, solvent, pH, and competing components. In particular, anion recognition allowed disassembly and thus led to a significant decrease of UCST in dimethyl sulfoxide, and the combination of anion and solvent effects offered additional handle for control. Moreover, the use of anions, cations, as well as pH change was employed for the modulation of LCST-type polymer in water. Furthermore, switching on/off thermoresponsiveness was readily achieved by dynamic covalent exchange. Mechanistic studies also shed light on stimuli-induced changes in aggregation behaviors. Finally, thermally controlled encapsulation and release of hydrophobic and hydrophilic dyes were realized with great repeatability and reversibility, respectively, showing potential in delivery and sensing. The results and strategies described should provide opportunities for many aspects, including dynamic assemblies, complex systems, and adaptive materials.

Axial chirality is a prevalent and important phenomenon in chemistry. Herein we report a combination of dynamic covalent chemistry and axial chirality for the development of a versatile platform for the binding and chirality sensing of multiple classes of mononucleophiles. An equilibrium between an open aldehyde and its cyclic hemiaminal within biphenyl derivatives enabled the dynamic incorporation of a broad range of alcohols, thiols, primary amines, and secondary amines with high efficiency. Selectivity toward different classes of nucleophiles was also achieved by regulating the distinct reactivity of the system with external stimuli. Through induced helicity as a result of central-to-axial chirality transfer, the handedness and ee values of chiral monoalcohol and monoamine analytes were reported by circular dichroism. The strategies introduced herein should find application in many contexts, including assembly, sensing, and labeling.

Molecular switches are an intensive area of research, and in particular, the control of multistate switching is challenging. Herein we introduce a general and versatile strategy of dynamic covalent switches and communicating networks, wherein distinct states of reversible covalent systems can induce addressable fluorescence switching. The regulation of intramolecular ring/chain equilibrium, intermolecular dynamic covalent reactions (DCRs) with amines, and both permitted the activation of optical switches. The variation in electron-withdrawing competition between the fluorophore and 2-formylbenzenesulfonyl unit afforded diverse signaling patterns. The combination of switches

Achieving complexity is central to the creation of chemical systems, inspired by natural systems. Herein we introduce a strategy of switchable orthogonal dynamic covalent chemistry (DCC) toward the regulation of complex dynamic networks. The control of dual reactivity of tautomers and resulting pathways allowed reversible covalent bonding of a large scope of primary amines, secondary amines, alcohols, and thiols with high efficiency. The selection of reaction pathways next enabled the realization of orthogonal but switchable dynamic covalent reactions (DCRs) with nucleophile pairs of amine/alcohol, alcohol/thiol, and amine/thiol by varying protonation and oxidation states. Control experiments confirmed the crucial role of dual reactivity on the stability and switchability of DCRs. The specificity toward amines, alcohols, and thiols, as well as interconversion between their corresponding assemblies, was further accomplished in one vessel, thus creating tunable communicating networks with three types of DCRs. Moreover, the switchable orthogonality combined with differential reactivity of multiple sulfonamides and nucleophiles enhanced the complexity within dynamic libraries. The generality and versatility of our approaches should facilitate their incorporation into many aspects of chemistry endeavors.

For producing flexible memory materials with controlled memory characteristics, functional copolynaphthalimides (co-PNIs), with varied composition of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), 4,4′-(9-fluorenylidene) dianiline (BAPF) and 4,4′-diaminotriphenylamine (DATPA), were designed and synthesized in this work. Optical and electrochemical measurements on the synthesized co-PNIs, denoted as co-PNI-TPAx (where x = 0, 1, 2, 5, 10 for the molar ratio of the DATPA-containing unit in the co-PNIs), indicate gradually enhanced HOMO and continually degraded band gap with increasing DATPA unit, as further approved by molecular simulation. What is more, electrical characterization on the ITO | thin co-PNI active layer | Al sandwich devices witnesses a wide alteration of the memory behaviors from no electrical bistability (NULL, co-PNI-TPA0 and co-PNI-TPA1), to static random access memory (SRAM, co-PNI-TPA2 and co-PNI-TPA5), and then to the write-once read-many times memory (WORM, co-PNI-TPA10), implying the significance of composition control on determining the memory characteristics. Mechanisms associated with the switching effect and the charge transfer in the co-PNIs were analyzed based on the optical, electrochemical results and the B3LYP/6–31G(d) calculations. The conversion of the memory effect from NULL, to volatile SRAM, and then to nonvolatile WORM is suggested to result from the gradually increased ability of the synthesized co-PNIs to form stable charge transfer complexes with the increased electron-donating DATPA species. The fine memory tuning achieved here reveals the particular availability of the copolymerization strategy in designing functional polyimides with controlled performances for practical memory applications.

A functional polyimide (6F/CzTPA PI), 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA)/ 4,4′-diamino-4″-N-carbazolyltriphenylamine (DACzTPA), was synthesized in our present work for electrical resistive memory device applications. Semiconductor parameter analysis on the polyimide memory devices indicates that the synthesized polyimide possesses a volatile static random access memory (SRAM) characteristic with an ON/OFF current ratio of about 10 5 at the threshold voltage of around 1.5 V and −1.8 V. In addition, the device using the 6F/CzTPA PI as the active layer reveals excellent long-term operation stability with the endurance of reading cycles up to 10 8 under a voltage pulse and retention times for at least 8 h under constant voltage stress (−1 V). The charge transfer mechanisms and the roles of the donor and acceptor components in the PI macromolecules associated with the electrical switching effect are elucidated on the basis of the experimental and quantum simulation results.

Herein we report for the first time the use of dynamic covalent reactions (DCRs) for building a π-stacking model system and further quantifying its substituent effects (SEs), which remain a topic of debate despite the rich history of stacking. A general DCR between 10-methylacridinium ion and primary amines was discovered, in which π-stacking played a stabilizing role. Facile quantification of SEs with in situ competing π-stacking systems was next achieved in the form of amine exchange exhibiting structural diversity by simply varying components. The linear correlation with σm in Hammett plots indicates the dominance of purely electrostatic SEs, and the additivity of SEs is in line with the direct interaction model. With α-chiral amines π-stacking within the adduct enabled chirality transfer from homotopic faces. The strategy of dynamic covalent assembly should be appealing to future research of probing weak interactions and manipulating chirality.

Dynamic covalent chemistry (DCC) has become a powerful tool for the creation of molecular assemblies and complex systems in chemistry and materials science. Herein we developed for the first time quantitative reactivity scales capable of correlation and prediction of the equilibrium of dynamic covalent reactions (DCRs). The reference reactions are based upon universal DCRs between imines, one of the most utilized structural motifs in DCC, and a series of O-, N-, and S- mononucleophiles. Aromatic imines derived from pyridine-2-carboxyaldehyde exhibit capability for controlling the equilibrium through distinct substituent effects. Electron-donating groups (EDGs) stabilize the imine through quinoidal resonance, while electron-withdrawing groups (EWGs) stabilize the adduct by enhancing intramolecular hydrogen bonding, resulting in curvature in Hammett analysis. Notably, unique nonlinearity induced by both EDGs and EWGs emerged in Hammett plot when cyclic secondary amines were used. This is the first time such a behavior is observed in a thermodynamically controlled system, to the best of our knowledge. Unified quantitative reactivity scales were proposed for DCC and defined by the correlation log K = S(N) (R(N) + R(E)). Nucleophilicity parameters (R(N) and S(N)) and electrophilicity parameters (R(E)) were then developed from DCRs discovered. Furthermore, the predictive power of those parameters was verified by successful correlation of other DCRs, validating our reactivity scales as a general and useful tool for the evaluation and modeling of DCRs. The reactivity parameters proposed here should be complementary to well-established kinetics based parameters and find applications in many aspects, such as DCR discovery, bioconjugation, and catalysis.

Lanthanide (Ln(3+))-doped nanoparticles (NPs) are an intensive area of research in chemical and materials sciences. Herein a sensor array of Ln(3+)-doped NPs was developed for the first time toward sensitive molecular sensing based on a novel strategy of the hybridized time-resolved Förster resonance energy transfer (TR-FRET) with the indicator displacement assay (IDA) concept (TR-FRET-IDA). The sensor platform was generated in situ by binding a series of negatively charged indicators on the surface of ligand-free LiYF4:Ce/Tb NPs. The TR-FRET between NPs and dyes resulted in indicator emission and was employed as a means of removing undesired short-lived background luminescence from the indicator effectively. Displacement of indicators from the NP/indicator ensembles by glyphosate, a common herbicide, led to turn-off of the indicator emission. The sensor array was able to successfully discriminate 11 biologically relevant anions with high accuracy and sensitivity in pure aqueous buffer both qualitatively and quantitatively. Furthermore, the differentiation of six model proteins in the nM range was achieved with 100% accuracy for the classification, thereby demonstrating the versatility of this simple sensor platform. The study of the mechanism of binding and signal modulation further verified TR-FRET-IDA as a reliable sensing paradigm.

In an effort to develop reactivity-based dynamic covalent bonding and to expand the scope and application of the dynamic covalent chemistry, in situ-generated simple generic iminium ions were utilized for the dynamic covalent binding of monoalcohols with high affinity. Hammett analysis was conducted to manipulate the equilibrium and correlate with the reactivity of reactants. The structural features of aldehydes and secondary amines were identified, and both polar and steric effects have significant impact on the binding. In particular, the substrates which can participate in π-π and polar-π interactions are able to afford apparent equilibrium constants in the magnitude of 10(4) M(-2), demonstrating the power of weak supramolecular forces to stabilize the dynamic covalent assembly. The generality of the assembly was validated with a series of mono secondary alcohols. To showcase the practicality of our system, chirality discrimination and ee measurement of chiral secondary alcohols were achieved.

Two novel functional aromatic polyimides (PIs), 6F-αNA PI and 6F-βNA PI, in which the hexafluoroisopropylidene-diphthalic anhydride (6FDA) serves as the electron-accepting unit and the diphenylnaphthylamine (DPNA) functions as the electron-donating species, were synthesized for memory device applications. The 6F-αNA PI shows distinct electrical bistable states with an ON/OFF current ratio up to 106, and can be switched on bi-directionally with no polarity, which could be applied as the nonvolatile write-once read-many times (WORM) memory. Whereas, the 6F-βNA PI-based memory device exhibits flash type memory characteristics with a switching-on voltage at ca. 1.1 V and an ON/OFF ratio of 104. Both polyimides exhibit good long-term operation stability, survive up to 108 reading cycles with no current degradation, and show ultrafast switching with a response time less than 20 ns. Mechanisms associated with the electrical switching behaviors are discussed on the basis of the experimental and quantum simulation results. The electric-field-induced electronic transition from diphenylnaphthylamine units to hexafluoropropylidene phthalimide units and the subsequent formation of charge-transfer complexes are supposed to be responsible for the observed electrical memory effects. Molecular simulation suggests that α-tethering of the naphthyl group results in more non-coplanar conformation of the DPNA species in the 6F-αNA PI, as compared to that of the β-tethering in the 6F-βNA PI, therefore producing a higher energy barrier that prevents the back charge transfer processes, consequently leading to the WORM vs. flash memory behaviors. The 6F-αNA PI differs from 6F-βNA PI only in the substitution position of the naphthyl group, i.e., α-tethering vs. β-tethering. The distinct memory effects observed here suggest the significance of the electron-donating structures on the memory effects, and the tailorability of the memory characteristics through fine structure adjustment.