A large triangular arylene–ethynylene macrocycle featuring unique circularly arranged –[D–π–A]3– electronic characteristics is designed and synthesized. The shape-persistent π-conjugated backbone is composed of alternating electron-rich dialkoxyphenanthrene and electron-deficient dicyanodibenzo[f,h]quinoxaline units, connected by ethynylene linkers. The synthesis of such a special macrocyclic molecule is realized by employing a post-cyclization functional group installation strategy. The absorption and emission spectra of the macrocycle are found sensitively dependent on the solvent polarity. By virtue of a conjugated π-scaffold and a cyclic –[D–π–A]3– motif, evident two-photon absorption (2PA) and two-photon excitation fluorescence properties are exhibited, with a 2PA cross section maximum of 3 × 103 GM determined by the Z-scan method.

AbstractThe self-assembly of short peptide offers versatile processes for adjusting the ordered stacking of organic functional materials to enhance photoinduced electron transfer. Herein, this study presents the first demonstration of the use of Aβ16–22 peptide to prepare polythiophene/Aβ16–22 assemblies for a photocatalytic water splitting system. Isothermal titration microcalorimetry results show that the driving forces for polythiophene/Aβ16–22 assembly formation are electrostatic interactions, as well as hydrogen bonds and hydrophobic interactions. The assemblies accelerate the photoinduced electrons transfer from polythiophene upon light excitation and eventually enhance the hydrogen evolution. This work opens a new way into the development of biohybrid materials as novel photocatalytic water splitting platform for hydrogen evolution.

Heavy-atom-free triplet photosensitizers are developed by harnessing the thermally active triplet state of carbazolyl dicyanobenzene (CDCB) derivatives and applied to realize visible-to-ultraviolet photon upconversion (UC) via triplet–triplet annihilation (TTA). Demonstrating an annihilator-appending strategy, the designed sensitizers effectively realize TTA UC in polyurethane films with 2,7-di-tert-butylpyrene (DBP) as the annihilator/emitter. The covalently tethered DBP to CDCB is proven critical for achieving the superior sensitizing and UC performance in the solid matrix, essentially by suppressing the reverse ISC and more effectively transferring triplet excitons to free emitters.

The novel multi-colored switching mechanochromic materials were obtained based on a spiropyran and pyrene derivative. The mechanochromic behaviors under either isotropic compression or anisotropic grinding were realized through a combination of supramolecular and chemical structural changes. The high pressure achieved by utilizing the Diamond Anvil Cell technique induced a continuous mechanochromic process involving a color change from blue to red, while the tricolored switching could be achieved by sequential light or heavy grinding of the sample powder. The mechanochromic behaviors could be adjusted via the control of the modes and strength of the mechanical loadings. This molecule showcases a novel straightforward strategy for the design of multi-colored switching molecules and the control of mechanochromism under pressure based on both supramolecular changes and molecular structural changes. It shows great potential for applications in pressure sensors, pressure calibration, mechanoprobes and security inks.

Efficient visible-to-UV photon upconversion via triplet–triplet annihilation (TTA) is accomplished in polyurethane (PU) films by developing new, powerful photosensitizers fully functional in the solid-state matrix. These rationally designed triplet sensitizers feature a bichromophoric scaffold comprising a tris-cyclometalated iridium(III) complex covalently tethered to a suitable organic small molecule. The very rapid intramolecular triplet energy transfer from the former to the latter is pivotal for achieving the potent sensitizing ability, because this process out-competes the radiative and nonradiative decays inherent to the metal complex and produces long-lived triplet excitons localized with the acceptor moiety readily available for intermolecular transfer and TTA. Nonetheless, compared to the solution state, the molecular diffusion is greatly limited in solid matrices, which even creates difficulty for the Dexter-type intramolecular energy transfer. This is proven by the experimental results showing that the sensitizing performance of the bichromophoric molecules strongly depends on the spatial distance separating the donor (D) and acceptor (A) units and that incorporating a longer linker between the D and A evidently curbs the TTA upconversion efficiency in PU films. Using a rationally optimized sensitizer structure in combination with 2,7-di-tert-butylpyrene as the annihilator/emitter, the doped polyurethane (PU) films demonstrate effective visible-to-UV upconverted emission signal under noncoherent-light irradiation, attaining an upconversion quantum yield of 2.6%. Such quantum efficiency is the highest value so far reported for the visible-to-UV TTA systems in solid matrices.Keywords: iridium complex; photon upconversion; solid matrix; triplet sensitizer; triplet−triplet annihilation

The photophysics of a series of bichromophoric molecules featuring an intramolecular triplet energy transfer between a triscyclometalated iridium(III) complex and covalently linked organic group are studied. By systematically varying the energy gap (0.1–0.3 eV) between the donor (metal complex) and acceptor (pyrene unit), reversible triplet energy transfer processes with equilibrium constant K ranging from ca. 500 to 40 000 are established. Unique photophysical consequences of such large K values are observed. Because of the highly imbalanced forward and backward energy transfer rates, triplet excitons dominantly populate the acceptor moiety in the steady state, giving rise to ultralong luminescence lifetimes up to 1–4 ms. Because the triscyclometalated Ir and triplet pyrene groups both impart relatively small nonradiative energy loss, decent phosphorescence quantum yields (Φ = 0.1–0.6) are attained in spite of the exceptionally prolonged excited states. By virtue of such precious combination of long-lived triplet state and high Φ, these bichromophoric molecules can serve as highly sensitive luminescent sensors for detecting trace amount of O2 and as potent photosensitizers for producing singlet oxygen even under low-oxygen content conditions.Keywords: oxygen sensor; photosensitizer; triplet energy transfer; triplet lifetime; triscyclometalated iridium

A series of neutral binuclear nickel phenoxyiminato catalysts connected by rigid skeletons of different lengths have been efficiently synthesized. The rigid skeleton and bulky tert-butyl groups together force two nickel coordination planes to get close and stack in an anti cofacial fashion. With reduced nickel–nickel distances, these binuclear nickel complexes displayed higher catalytic activity, produced polymers with higher molecular weight, and showed less inhibition by the presence of additional polar monomers in ethylene polymerization and copolymerization. We attributed these effects to a favorable consequence of the enhanced bimetallic effect and steric hindrance due to the cofacial orientation.

The isomerization of spiropyrans in crystals was realized under high pressure, and the corresponding mechanochromic response could be observed by the naked eye. In situ UV-Vis spectroscopy study demonstrated that the equilibrium constant increases with the increasing pressure, from which we proposed that the negative volume of reaction determined the isomerization under high pressure.

Unusual anti-1,4-adducts of anthracene derivatives and anti-adducts of inert arenes with rigid scaffolds have been obtained via AlCl3-assisted Diels–Alder reaction in good to excellent yields under mild conditions. Further derivation of 1,4-adducts gave π-conjugated polymers which could act as sensors of explosive species. This highly efficient synthesis method provides versatile approaches to solid-state emissive π-conjugated polymers.

A series of neutrally charged Ni(II) phenoxyiminato catalysts with fluorine atoms at different positions on the N-terphenyl motif are synthesized, and their abilities to polymerize ethylene are compared. At 25 °C, the ortho-fluorinated Ni-5F, Ni-3F′, and Ni-2F achieve significantly higher polymerization activities than Ni-3F and Ni-0F. In addition, branch density and molecular weight of the obtained polyethylenes vary gradually in the order of Ni-5F, Ni-3F, Ni-3F′, Ni-2F, and Ni-0F. Based on the X-ray crystal structure and 19F NMR spectra, the ortho fluorine atoms are found to make terphenyl groups more rigid and bulky. Theoretical calculations suggest that the increased steric bulk of terphenyl motif leads to an increase in the ground state energy of the resting state species relative to the migratory insertion transition state, and consequently, lowered migratory insertion barriers are expected in Ni-5F, Ni-3F′, and Ni-2F. On the other hand, the weak hydrogen bonding between the ortho fluorine atoms and coordinated ethylene in insertion transition state is also proposed in favor of insertion. Similar to previous reports, polyethylene microstructure was mainly related to electronic effects of fluorine atoms.

We studied high-pressure reaction of solid cyanamide in a diamond anvil cell up to a pressure of 21.7 GPa. The results of in situ high-pressure Raman spectroscopy and angle-dispersive X-ray diffraction experiments indicated the occurrence of pressure-induced oligomerization in cyanamide over 13 GPa. The Raman, NMR, and UV absorption spectra of recovered samples confirmed that the chemical reaction was irreversible and that the high-pressure products contained C═N bonds. Subsequently, results of kinetic studies showed the relation between pressure and the reaction rate. Meanwhile dependence of activation volume with pressure indicated that the steric factors affected the reaction. Additionally, the increase in the amount of C–C bonds of recovered samples was attributed to the change of reactive sites of adjacent C≡N groups. These results suggest that the application of pressure can tune both the reactive sites and the reaction rate to affect oligomerization and even other chemical reactions.

Molecular assemblies with well-defined structures capable of photo-induced electron transfer and charge transport or photochemical reactions are reviewed. Hierarchical supramolecular architectures, which assemble the modular units into specific spatial arrangements and facilitate them to work cooperatively, are vital for the achievement of photo-functions in these systems. The chemical design of molecular building blocks and noncovalent interactions exploited to realize supramolecular organizations are particularly discussed. Reviewing and recapitulating the chemical evolution traces of these accomplished systems will hopefully delineate certain fundamental design principles and guidelines useful for developing more advanced functions in the future.

Enhanced triplet–triplet annihilation upconversion efficiency is achieved with two tris-cyclometalated iridium sensitizers covalently tethered with a pyrene annihilator. The improved sensitizing ability and very long phosphorescence lifetimes (1–2 ms) of these bichromophore molecules are both attributed to the intramolecular energy transfer between the iridium complex and appended pyrene group.

Unusual regio- and stereo-selectivity in Diels–Alder (D–A) reactions were achieved between bulky N-phenylmaleimides and anthracene derivatives. Using multiple substituents with steric hindrance on both diene and dienophile, a noticeable shift toward 1,4-addition was successfully obtained. The substrate scope in this reaction was broad and the highest yield of anti-1,4-adducts was over 90%. Novel structures of anti-1,4-adducts were confirmed by single crystal X-ray diffraction analysis. This study not only provides the first reported method of synthesizing anti-1,4-adducts and achieving otherwise unattainable regio- and stereo-selectivity, but also elucidates the importance of combining the steric effects of two reactants to shift products toward 1,4-adducts. Moreover, the resulting 1,4-adducts could be further functionalized through their halogen groups via carbon–carbon coupling reactions.

Metal-free 1,3-dipolar cycloaddition polymerization with controlled regioselectivity is achieved by pre-organizing azide and terminal alkyne functional groups in the solid state. Soluble polymers are obtained with monomers containing flexible tri- and tetra-ethylene glycol linkers.

To get highly ordered organic structures at the nanoscale, a series of new electronic donor–acceptor (D–A) dyads were synthesized. The dyads bearing different side chains (lipophilic or amphiphilic) or linkers (Long or Short) showed variable self-assembly behaviour. Long-linker dyads can fold in dilute solution, but the folding of short-linker dyads was not observed. Intermolecular D–A interactions and acceptor–acceptor (A–A) aggregation were proved to co-occur in chloroform for all four dyads. In the bulk state, amphiphilic dyads could overcome the intrinsic D–A interactions and achieve better D–A phase separation than lipophilic ones due to the incompatibility of the side chains. The dyad with a short-linker and amphiphilic side chains, Samphi, had the ability to form a gel, and both of the amphiphilic dyads could form nanofibres.

A series of homoligated (1c–1e) and heteroligated (2a–2e) salicylaldiminato titanium dichloride complexes with different substituents ortho to the phenoxy oxygens were efficiently prepared. X-ray diffraction studies on these new dichloride complexes 2b, 2d, and 2e reveal a distorted octahedral coordination of the central metal. In the presence of dried methylaluminoxane, all the complexes exhibit high ethylene polymerization productivities. Surprisingly, complex 1d incorporating an o-(trimethylsilyl)ethynyl group displays the highest activity [5.26 × 103 kg of polyethylenes (mol Ti)−1 h–1]. In ethylene/1-hexene copolymerization, the heteroligated complexes 2a–2e display improved activities and intermediate incorporation ability compared with their homoligated counterparts 1a–1f. The activity and incorporation ability for 1-hexene are highly dependent on the nature of the ortho-substituents. Among them, (trimethylsilyl)ethynyl-substituted precatalyst (1d) achieves the highest incorporation ratio (27.3 mol %), while ethynyl-substituted precatalyst (2c) achieves the highest copolymerization activity [2.89 × 103 kg of copolymers (mol Ti)−1 h–1].

The cycloaddition of azides and alkynes in the solid state was accelerated by high pressure. In situ Raman scattering and synchrotron X-ray diffraction were employed to study reaction kinetics at different pressures which revealed that the pressure acceleration originates from the elevated substrate energy and decreased activation energy.

We report a rapid and selective preparation of a 1:2 charge transfer (CT) complex from anthracene and 5,6,7,8-tetrafluoro-1,4-anthraquinone, either through a solution process or from mechanical grinding of the binary mixture. Moreover, CT complex formation inhibits the Diels–Alder reaction in the crystalline state.

•Two water soluble mercapto group probes have been developed.•The fluorescent probes are able to distinguish proteins with two close mercapto groups and those with a single mercapto group.•We used these probes to detect metallothionein which has multiply mercapto groups and distinguish it from BSA which has only one free mercapto group.•We also introduced the concept of functional group combination detection.Two water soluble fluorescent probes with quaternary ammonium salts as solubilization groups were designed and synthesized to detect proteins with close mercapto groups. The unique structure of V-shape oligo(o-phenylene-ethynylene) backbone connecting two maleimide groups as mercapto group recognition sites enables the probes to distinguish a single mercapto group from two close mercapto groups in proteins. The probe had no fluorescence response to proteins with only one mercapto group, but had strong fluorescence response to proteins with mercapto group combination at the concentration of 10−6 mol/L. The probe worked under a wide range of pH, from 4 to 8. This work also demonstrates the concept of functional group combination detection.

We have designed a supramolecular system to pre-organize the azide and alkyne functional groups via electrostatic and arene–perfluoroarene interactions. After pre-organization, high pressure was applied to accelerate the copper-free cycloaddition of the azide and alkyne groups in the crystalline state.

A phenyl and a 2,3,5,6-tetrafluorophenyl ring, each bearing a tris(n-dodecyloxy)benzylamine moiety via an amide bond, were tethered together through an imine linkage to give a non-covalent synthon (imine 1) with a strong capacity of supramolecular self-assembly. Gelation was observed in several organic solutions, within which fibrous aggregate morphologies were visualized by SEM and AFM. Both arene–perfluoroarene stacking and amide–amide hydrogen bonding interactions were responsible for such self-assembly behaviours, as evidenced by 1H NMR studies. Hydrolysis of the imine linkage catalyzed by acid strongly weakened the intermolecular interactions, resulting in dissociation of the low molecular weight gelator and giving rise to an acid-mediated gel–sol transition.

We have developed an absorption spectrum based molecular ruler that measures the distance between two mercapto groups. The conformation of the molecular rulers changes with the distance, which induces an absorption spectrum change. DFT calculation has been carried out to elucidate the relation between the molecular conformation and the absorption spectrum. With this simple method, we can estimate the distance between two mercapto groups on the scale of 0.4–1 nm. This method can also be used to monitor conformation transition, which is demonstrated by a silver ion titration experiment.

A binuclear heteroligated titanium(IV) catalyst based on phenoxyimine ligands (FI2-Ti2) with its crystal structure elucidated has been developed for the first time for olefin (co)polymerization. In ethylene polymerization, the activity of the binuclear catalyst FI2-Ti2 can reach 3.0 × 106 g mol–1 h–1, and the polydispersity of the resulting polymers is narrow. In copolymerization of ethylene and other olefins, similar incorporation ratios for monoenes are obtained for FI2-Ti2 and FI-Ti1. However, the incorporation ratio of 1,5-hexadiene increases from 3.2% using FI-Ti1 to 8.8% with FI2-Ti2. In comparison, the binuclear monophenoxyimine catalyst, [FI2-Ti2(THF)2], exhibits higher catalytic activity and incorporates more α-olefins than its mononuclear analogue [FI-Ti1(THF)] in the copolymerization. These results are interpreted as consequences of two effects. First, the cooperativity between the two metal centers facilitates the coordination of olefin. Second, the substitutions near the active sites exert a steric effect by blocking and suppressing the binding of comonomers.

A novel type of chiral layered supramolecular copolymer with high molecular weight has been assembled from a hydrogen bonded C6-symmetric zinc porphyrin hexamer and chiral C3-symmetric pyridine hexadentate linkers driven by multivalent zinc porphyrin–pyridine coordination. UV–vis, circular dichroism, and static light scattering experiments revealed that the formation of the layered supramolecular copolymers is at first dynamically controlled and then becomes thermodynamically controlled.

The separation and sequencing of DNA are the main objectives of the Human Genome Project, and this project has also been very useful for gene analysis and disease diagnosis. Capillary electrophoresis (CE) is one of the most common techniques for the separation and analysis of DNA. DNA separations are usually achieved using capillary gel electrophoresis (CGE) mode, in which polymer gel is packed into the capillary. Compared with a traditional CGE matrix, a hydrophilic polymer matrix, which can be adsorb by the capillary wall has numerous advantages, including stability, reproducibility and ease of automation. Various water-soluble additives, such as linear poly(acrylamide) (PAA) and poly(N,N-dimethylacrylamide) (PDMA), have been employed as media. In this study, different star-shaped PDMA polymers were designed and synthesized to achieve lower polymer solution viscosity. DNA separations with these polymers avoid the disadvantages of high viscosity and long separation time while maintaining high resolution (10 bp between 271 bp and 281 bp). The influences of the polymer concentration and structure on DNA separation were also determined in this study; higher polymer concentration yielded better separation performance, and star-like polymers were superior to linear polymers. This work indicates that modification of the polymer structure is a potential strategy for optimizing DNA separation.

Honeycomb films fabricated with small molecules via the breath figure (BF) method are reported. Water droplet templates were stabilized by self-assembled supramolecular architectures and a subsequent gelation process. The formed honeycomb film features a hydrogen bonded network of a dynamic nature.

Well-defined 3-dimensional architectures constitute the indispensable structural basis of the versatile, mind-boggling functions of biological macromolecules, such as proteins and nucleic acids. In the past few decades, diversified synthetic systems have been designed to mimic these biological entities in their capability of adopting such specific, higher order structures. The relevant research field presents one of the most rapidly developing areas related to supramolecular chemistry. The current contribution will focus on the most recent progress related to foldamers consisting of arylene ethynylene building blocks. Some of the work features developing novel functions based on previously established arylene ethynylene folding systems, and others have designed and synthesized new arylene ethynylene foldable structures that aim to realize previously uncharted properties.

Facilitated by arene–perfluoroarene interactions, a 1,3-dipolar cycloaddition between azide and alkyne proceeded in the crystals at room temperature in the absence of a copper(I) catalyst, and the reaction was confirmed to be a highly regioselective process giving the 1,4-triazole product.

We have developed an absorption spectrum based molecular ruler that measures the distance between two mercapto groups. The conformation of the molecular rulers changes with the distance, which induces an absorption spectrum change. DFT calculation has been carried out to elucidate the relation between the molecular conformation and the absorption spectrum. With this simple method, we can estimate the distance between two mercapto groups on the scale of 0.4–1 nm. This method can also be used to monitor conformation transition, which is demonstrated by a silver ion titration experiment.

Heavy-atom-free triplet photosensitizers are developed by harnessing the thermally active triplet state of carbazolyl dicyanobenzene (CDCB) derivatives and applied to realize visible-to-ultraviolet photon upconversion (UC) via triplet–triplet annihilation (TTA). Demonstrating an annihilator-appending strategy, the designed sensitizers effectively realize TTA UC in polyurethane films with 2,7-di-tert-butylpyrene (DBP) as the annihilator/emitter. The covalently tethered DBP to CDCB is proven critical for achieving the superior sensitizing and UC performance in the solid matrix, essentially by suppressing the reverse ISC and more effectively transferring triplet excitons to free emitters.

Enhanced triplet–triplet annihilation upconversion efficiency is achieved with two tris-cyclometalated iridium sensitizers covalently tethered with a pyrene annihilator. The improved sensitizing ability and very long phosphorescence lifetimes (1–2 ms) of these bichromophore molecules are both attributed to the intramolecular energy transfer between the iridium complex and appended pyrene group.

The isomerization of spiropyrans in crystals was realized under high pressure, and the corresponding mechanochromic response could be observed by the naked eye. In situ UV-Vis spectroscopy study demonstrated that the equilibrium constant increases with the increasing pressure, from which we proposed that the negative volume of reaction determined the isomerization under high pressure.

Facilitated by arene–perfluoroarene interactions, a 1,3-dipolar cycloaddition between azide and alkyne proceeded in the crystals at room temperature in the absence of a copper(I) catalyst, and the reaction was confirmed to be a highly regioselective process giving the 1,4-triazole product.

Unusual regio- and stereo-selectivity in Diels–Alder (D–A) reactions were achieved between bulky N-phenylmaleimides and anthracene derivatives. Using multiple substituents with steric hindrance on both diene and dienophile, a noticeable shift toward 1,4-addition was successfully obtained. The substrate scope in this reaction was broad and the highest yield of anti-1,4-adducts was over 90%. Novel structures of anti-1,4-adducts were confirmed by single crystal X-ray diffraction analysis. This study not only provides the first reported method of synthesizing anti-1,4-adducts and achieving otherwise unattainable regio- and stereo-selectivity, but also elucidates the importance of combining the steric effects of two reactants to shift products toward 1,4-adducts. Moreover, the resulting 1,4-adducts could be further functionalized through their halogen groups via carbon–carbon coupling reactions.

Based on bioorthogonal tetrazine ligation, a pre-targeted anchor strategy was developed to regulate the intracellular distribution of bioactive molecules. This strategy could solve the issue regarding the permeability and targeting ability of bioactive molecules in the specific organelles of living cells.

The cycloaddition of azides and alkynes in the solid state was accelerated by high pressure. In situ Raman scattering and synchrotron X-ray diffraction were employed to study reaction kinetics at different pressures which revealed that the pressure acceleration originates from the elevated substrate energy and decreased activation energy.

Molecular assemblies with well-defined structures capable of photo-induced electron transfer and charge transport or photochemical reactions are reviewed. Hierarchical supramolecular architectures, which assemble the modular units into specific spatial arrangements and facilitate them to work cooperatively, are vital for the achievement of photo-functions in these systems. The chemical design of molecular building blocks and noncovalent interactions exploited to realize supramolecular organizations are particularly discussed. Reviewing and recapitulating the chemical evolution traces of these accomplished systems will hopefully delineate certain fundamental design principles and guidelines useful for developing more advanced functions in the future.

The novel multi-colored switching mechanochromic materials were obtained based on a spiropyran and pyrene derivative. The mechanochromic behaviors under either isotropic compression or anisotropic grinding were realized through a combination of supramolecular and chemical structural changes. The high pressure achieved by utilizing the Diamond Anvil Cell technique induced a continuous mechanochromic process involving a color change from blue to red, while the tricolored switching could be achieved by sequential light or heavy grinding of the sample powder. The mechanochromic behaviors could be adjusted via the control of the modes and strength of the mechanical loadings. This molecule showcases a novel straightforward strategy for the design of multi-colored switching molecules and the control of mechanochromism under pressure based on both supramolecular changes and molecular structural changes. It shows great potential for applications in pressure sensors, pressure calibration, mechanoprobes and security inks.