Programmable photoresponsive materials based on a single molecule via distinct topochemical reactions.

Engineering the preorganization of photoactive units remains a big challenge in solid-state photochemistry research. It is of not only theoretical importance in the construction of topochemical reactions but also technological significance in the fabrication of advanced materials. Here, a cyanostilbene derivative, (Z)-2-(3,5-bis(trifluoromethyl)phenyl)-3-(naphthalen-2-yl) acrylonitrile (BNA), was crystallized into two polymorphs under different conditions. The two crystals, BNA-α and BNA-ß, have totally different intra-π-dimer and inter-π-dimer hierarchical architectures on the basis of a very simple monomer, which provides them with distinct reactivities, functions and photoresponsive properties. Firstly, two different types of solid-state [2 + 2] photocycloaddition reaction: (i) a typical olefin-olefin cycloaddition reaction within the symmetric π-dimers of BNA-α and (ii) an unusual olefin-aromatic ring cycloaddition reaction within the offset π-dimers of BNA-ß have been observed, respectively. Secondly, the crystal of BNA-α can be bent to 90° without any fracture, exhibiting outstanding flexibility upon UV irradiation, while the reversible photocycloaddition/thermal cleavage process (below 100 °C) accompanied by unique fluorescence changes can be achieved in the crystal of BNA-ß. Finally, micro-scale photoactuators and light-writable anti-counterfeiting materials have been successfully fabricated. This work paves a simple way to construct smart materials through a bottom-up way that is realized by manipulating hierarchical architectures in the solid state.

A cyanide-sensing detector in aqueous solution based on anion-π interaction-driven electron transfer.

A "turn on" fluorescent and colorimetric sensor, HAT(CN)6, was developed for the light-up detection of cyanide. It was implemented through its strong anion-π interaction, inducing thermal CN- → HAT(CN)6 electron transfer, to give the dianion product [HAT(CN)6]2-, which exhibits unexpected fluorescence. The sensor shows high selectivity, rapid response and a low detection limit towards CN- in aqueous solution, hence indicating its enormous potential in practical applications.

Multiple adaptation of constitutional dynamic networks and information storage in constitutional distributions of acylhydrazones.

We report a study of the behavior of four dynamic covalent libraries (DCLs) based on acylhydrazones aAbB and of the corresponding square constitutional dynamic networks (CDNs) NA-ND under the effect of three agents, namely, metal cations, base + metal cations and light irradiation; in particular, the successful switching of the CDN NB between two orthogonal distributions results, respectively, from metallo-selection and photo-selection. The four DCLs undergo triple adaptation when subjected to the three agents with the generation of specific CDN distributions characteristic of each of the four DCLs. The ternary outputs displayed by the DCLs present three states (-1, 0 and 1) related to three different constitutional distributions expressed in response to the triple inputs applied. This latter process amounts to the storage of molecular information in dynamic distributions rather than in selective interactions between complementary entities undergoing molecular recognition.

Higher Order Constitutional Dynamic Networks: [2×3] and [3×3] Networks Displaying Multiple, Synergistic and Competitive Hierarchical Adaptation.

The present study investigates the constitutional dynamic networks (CDNs) underlying dynamic covalent libraries (DCLs) that extend beyond the [2×2] case toward higher orders, namely [2×3] and [3×3] CDNs involving respectively six and nine constituents generated from the recombination of five and six components linked through reversible chemical reactions. It explores the behavior of such systems under the action of one or two effectors. More specifically and for the sake of proof of principle, it makes use of DCLs involving dynamic organic ligands and analyzes their single and double adaptive response under the action of one and two metal cation effectors. Thus, interconversions within [2×3] DCLs of six constituents (hydrazone, acylhydrazone, and imine ligands) give access to the generation of [2×3] CDNs of 3D trigonal prismatic type consisting of three [2×2] sub-networks and presenting specific responses to the application of Cu+ and Zn2+ metal cation effectors, in particular double agonistic amplification. More complex [3×3] CDNs based on nine ligand constituents of imine, hydrazone, and acylhydrazone types were also designed and subjected to the application of one or two effectors, e.g., Cu+ and Fe2+ metal cations, revealing novel types of adaptive behavior: (i) agonistic amplification between a single constituent and a full [2×2] sub-network, and (ii) agonistic amplification along a single diagonal connecting three constituents. Of special interest is also the dependence of the response of the system to hierarchical sequence of effector application, whereby initial interaction with Cu+ ions results in the destruction of the network, whereas the sequence Fe2+ followed by Cu+ yields a clean three-constituent DCL. Finally and strikingly, the present results also demonstrate that the increase in complexity of the system by introduction of an additional entity leads to a simpler output through dynamic competition between components.

A novel cascade strategy with supramolecular and chemodosimetric methods for designing a fluorescent ratiometric detector hypersensitive to trace water.

An intensely fluorescent zinc-salicylideneimine complex (-Zn(II)) was developed as a fluorescent ratiometric detector for the quantitative determination of trace water contents both in THF and methanol. It works based on a water-triggered cascade process: the dissociation reaction of the supramolecular ensemble and the subsequent hydrolysis reaction of its ligand.

A highly selective fluorescent sensor for Al³âº and the use of the resulting complex as a secondary sensor for PPi in aqueous media: its applicability in live cell imaging.

An easy-to-make salicylimine (L) bearing an "O-N-O"-coordination site was used as a highly selective fluorescent sensor for Al(3+) and PPi in aqueous solution. Sensor L showed a significant fluorescence enhancement in the presence of Al(3+) over other competitive metal ions. It works based on the Al(3+)-induced formation of a 1 : 1 L-Al(3+) complex, producing a chelation-enhanced fluorescence effect, the fluorescence quantum yield reached 0.59. This L-Al(3+) ensemble is a subsequent fluorescent sensor for PPi due to the strong attraction between Al(3+) and PPi, it can selectively discriminate PPi overcoming the interference of the biological competitors including PO4(3-), ADP and ATP at physiological pH. L and L-Al(3+) exhibit high sensitivity and selectivity for Al(3+) and PPi, the detection limits were found to be as low as 2.94 × 10(-8) M and 2.74 × 10(-7) M, respectively. It was further confirmed that sensor L had potential practical applications through mapping of Al(3+) in live cells.

A real-time fluorescent sensor specific to Mg2+: crystallographic evidence, DFT calculation and its use for quantitative determination of magnesium in drinking water.

An "off-the-shelf" fluorescence "turn-on" Mg(2+) chemosensor 3,5-dichlorosalicylaldehyde (BCSA) was rationally designed and developed. This proposed sensor works based on Mg(2+)-induced formation of the 2 : 1 BCSA-Mg(2+) complex. The coordination of BSCA to Mg(2+) increases its structural rigidity generating a chelation-enhanced fluorescence (CHEF) effect which was confirmed by single crystal XRD studies of the BSCA-Mg(2+) complex and TD/DFT calculations. This sensor exhibits high sensitivity and selectivity for the quantitative monitoring of Mg(2+) with a wide detection range (0-40 µM), a low detection limit (2.89 × 10(-7) mol L(-1)) and a short response time (<0.5 s). It can also resist the interference from the other co-existing metal ions, especially Ca(2+). Consequently, this fluorescent sensor can be utilized to monitor Mg(2+) in real time within actual samples from drinking water.

A dual channel optical detector for trace water chemodosimetry and imaging of live cells.

A novel 3-5-dichlorosalicylaldehyde Schiff base chemodosimeter (compound 1) for water is designed and synthesized, and it works based on a water-triggered reaction of a Schiff base. Addition of trace amounts of water into 1 in various organic solvents leads to a fluorescence turn-on response and a simultaneous dual-channel signal modulation (both in the fluorescence and absorption spectra). Especially, 1 is found to be an outstanding fluorescence enhancement water sensor in methanol with an extremely low detection limit of 22 ppm. Consequently this probe can be utilized to detect trace water in commercial methanol. The quantitative detection of a wide range of water content is enhanced in THF and acetonitrile (0-35% v/v for THF and 0-20% v/v for acetonitrile), where the fluorescence peak intensity is nearly proportional to the amount of water added. Moreover, 1 can be used for monitoring pH through a novel ON-OFF-ON type signal modulation both in fluorescence and absorption spectra within a wide pH detection range. Thus, the chemodosimeter can not only be utilized to monitor the intracellular pH fluctuations, but also to accomplish simultaneous in situ staining of the cytosol and acidic organelles in two different channels, respectively.