Junji Zhang

Photochromic Materials: More Than Meets The Eye

Photochromic materials are a family of compounds which can undergo reversible photo-switches between two different states or isomers with remarkably different properties. Inspired by their smart photo-switchable characteristics, a variety of light-driven functional materials have been exploited, such as ultrahigh-density optical data storage, molecular switches, logic gates, molecular wires, optic/electronic devices, sensors, bio-imaging and so on. This review commences with a brief description of exciting progress in this field, from systems in solution to modified functional surfaces. Further development of these photo-switchable systems into practical applications as well as existing challenges are also discussed and put in prospect.

Unsymmetrical diarylethenes as molecular keypad locks with tunable photochromism and fluorescence via Cu2+ and CN- coordinations.

New unsymmetrical diarylethenes were synthesized and their photochromic and fluorescent properties are tailored by Cu(2+) and CN(-) coordinations. A novel molecular logic keypad lock is constructed based on the fluorescence emission changes by the inputs of UV/visible irradiation, Cu(2+) and CN(-).

Nanopore-Based Sequencing and Detection of Nucleic Acids

Nanopore-based techniques, which mimic the functions of natural ion channels, have attracted increasing attention as unique methods for single-molecule detection. The technology allows the real-time, selective, high-throughput analysis of nucleic acids through both biological and solid-state nanopores. In this Minireview, the background and latest progress in nanopore-based sequencing and detection of nucleic acids are summarized, and light is shed on a novel platform for nanopore-based detection.

Soft mimic gear-shift with a multi-stimulus modified diarylethene

A novel gated photochromic compound Nap-Pip-DTE was prepared to mimic a soft gear-shift based on alternative UV/Vis irradiation, protonation/deprotonation and copper (II) ion complexation/dissociation. The fluorescence and absorption spectra were used as output signals. Copper (II) ion was introduced to mimic the parking (P) state by complexation with two intramolecular piperazine moieties of Nap-Pip-DTE, transforming diarylethene moieties into the photo-inactive parallel form.

Taking orders from light: progress in photochromic bio-materials

Photochromic materials are a family of compounds which undergo photo-reversible transformations between two different isomers with distinct physical and chemical properties. Most smart photochromic materials have been exploited in research areas such as electro-optical functional materials, while recently their applications have extended to novel bio-materials. Biological systems, such as tissue/cellular imaging, nucleotides, peptides, ion channels, etc., have emerged as a revolutionary research frontier for photochromic materials since both covalent coupling and non-covalent interactions with bio-molecules have been achieved. This review commences with a brief description of exciting progress in this field, and describes strategies for using photochromic functional molecules from bio-sensing and cell imaging to optical manipulation of bio-macromolecules (nucleotides, peptides, ion channels, GFP, etc.). Further development of these photo-switches as well as remaining challenges are also discussed and put in prospect.

Near-infrared photochromic behavior in a donor–acceptor type diarylethene modulated by the cyanide anion

Two new near-infrared (NIR) photochromic compounds, containing both electron-donating (D) and accepting groups (A), have been developed and their NIR photochromic and fluorescence performances can be modulated by the cyanide anion. Such a colorimetric cyanide sensor has been achieved based on this donor-photochromic bridge-acceptor system.

A Stimuli-Responsive Nanopore Based on a Photoresponsive Host-Guest System

The open-close states of the ion channels in a living system are regulated by multiple stimuli such as ligand, pH, potential and light. Functionalizing natural channels by using synthetic chemistry would provide biological nanopores with novel properties and applications. Here we use para-sulfonato-calix[4]arene-based host-guest supramolecular system to develop artificial gating mechanisms aiming at regulating wild-type α-HL commanded by both ligand and light stimuli. Using the gating property of α-hemolysin, we studied the host-guest interactions between para-sulfonato-calix[4]arene and 4, 4′-dipyridinium-azobenzene at the single-molecule level. Subsequently, we have extended the application of this gating system to the real-time study of light-induced molecular shuttle based on para-sulfonato-calix[4]arene and 4, 4′-dipyridinium-azobenzene at the single-molecule level. These experiments provide a more efficient method to develop a general tool to analyze the individual motions of supramolecular systems by using commercially available α-HL nanopores.

Optically activated uptake and release of Cu2+ or Ag+ ions by or from a photoisomerizable monolayer-modified electrode.

Di-(N-butanoic acid-1,8-naphthalimide)-piperazine dithienylethene was covalently linked to a cysteamine monolayer associated with a Au surface to yield a photoisomerizable monolayer composed of the open or closed dithienylcyclopentene isomers (3a or 3b), respectively. Electrochemical and XPS analyses reveal that the association of metal ions to the monolayer is controlled by its photoisomerization state. We find that Cu(2+) ions reveal a high affinity for the open (3a) monolayer state, K(a) = 4.6 × 10(5) M(-1), whereas the closed monolayer state (3b) exhibits a substantially lower binding affinity for Cu(2+), K(a) = 4.1 × 10(4) M(-1). Similarly, Ag(+) ions bind strongly to the 3a monolayer state but lack binding affinity for the 3b state. The reversible photoinduced binding and dissociation of the metal ions (Cu(2+) or Ag(+)) with respect to the photoisomerizable monolayer are demonstrated, and the systems may be used for the photochemically controlled uptake and release of polluting ions. Furthermore, we demonstrate that the photoinduced reversible binding and dissociation of the metal ions to and from the photoisomerizable electrode control the wettability properties of the surface.

Single molecule analysis of light-regulated RNA:spiropyran interactions

The photo-regulated interactions between an RNA aptamer and photochromic spiropyran were investigated at a single-molecule level via an α-hemolysin nanopore. Upon irradiation of alternating UV/visible light, the translocation process of the RNA aptamer could be optically tuned on account of its different binding affinity with two photoisomers, spiropyran and merocyanine. This provides a general analytic model for understanding the mechanism of a photo-regulated biomolecule conformational change at a single-molecule level.

Electrochemically triggered Au nanoparticles "sponges" for the controlled uptake and release of a photoisomerizable dithienylethene guest substrate.

1,2-Di(2-methyl-5-(N-methylpyridinium)-thien-3-yl)-cyclopentene undergoes a reversible photoisomerization between open and closed states. The closed isomer state exhibits electron acceptor properties, whereas its irradiation using visible light (λ > 530 nm) yields the open state that lacks electron acceptor features. The electropolymerization of thioaniline-functionalized Au nanoparticles (NPs) in the presence of the closed photoisomer state yields a molecularly imprinted Au NPs matrix, cross-linked by redox-active bis-aniline π-donor bridges. The closed isomer is stabilized in the imprinted sites of the bis-aniline-bridged Au NPs composite by donor-acceptor interactions. The electrochemical oxidation of the bis-aniline bridging units to the quinoid acceptor state leads to imprinted sites that lack affinity interactions for the binding of the closed state to the matrix, leading to the release of the closed photoisomer to the electrolyte solution. By the cyclic reduction and oxidation of the bridging units to the bis-aniline and quinoid states, the reversible electrochemically controlled uptake and release of the closed photoisomer is demonstrated. The quantitative uptake and release of the closed isomer to and from the imprinted Au NPs composites is followed by application of CdSe/ZnS quantum dots as auxiliary probes. Similarly, by the reversible photochemical isomerization of the closed substrate to the open substrate (λ > 530 nm) and the reversible photoizomerization of the open substrate to the closed state (λ = 302 nm), the cyclic photonic uptake and release of the closed substrate to and from the imprinted Au NPs matrix are demonstrated. Finally, we demonstrate that the electrochemically stimulated uptake and release of the closed substrate to and from the imprinted Au NPs composite controls the wettability of the resulting surface.