The precise control of molecular interaction and motion is a powerful strategy in the creation and development of intelligent materials. We demonstrate here a simple concept and approach to integrate intramolecular photochromic property with intermolecular aggregation-induced emission behaviors, with the aim to construct a new type of photoswitchable luminescent materials. This strategy is realized by the dithienylethene-bridged bispyridinium salt as photochromic molecular turnstile, and their subsequent fabrication into optically functional materials is reported. By restricting the rotation of central chemical bonds, the obtained molecular turnstile not only exhibits photocontrolled fluorescence emission through solvent exchange but is also capable of transforming into photowritable and photoerasable films in polymeric matrix with good recyclability. This functional molecular turnstile provides convenient routes to construct photochromic nanomaterials with controlled photophysical behaviors.

A [2]pseudorotaxane formed from an unsymmetrical diarylperfluorocyclopentene (1) and a Eu(3+) complex of terpyridinyldibenzo-24-crown-8 (2) revealed excellent reversible lanthanide luminescence switching behavior dual-modulated by host-guest and optical stimuli.

A series of water-soluble supramolecular assemblies were constructed from dithienylethene-modified permethyl-β-cyclodextrins and porphyrin derivatives, accompanied by a high FRET efficiency, and could be applied in the control of singlet oxygen generation in a 1% ethanol aqueous solution upon irradiation of different wavelength light. These findings will provide a feasible and convenient way to construct a potential photodynamic therapy material.

A photoswitchable supramolecular assembly can efficiently and reversibly switch on/off the luminescence of the [Ru(bpy)3]2+ center upon irradiation by light with different wavelengths in solution and the solid state. The assembly possesses reversible photoisomerization and a high Förster resonance energy transfer efficiency, and when used as an ink it can be reversibly and repeatedly erased and recovered by altering the wavelength of irradiation light.

Reversible noninvasive control over the generation of singlet oxygen is demonstrated in a bicomponent system comprising a diarylethene photochromic switch and a porphyrin photosensitizer by selective irradiation at distinct wavelengths. The efficient generation of singlet oxygen by the photosensitizer is observed when the diarylethene unit is in the colorless open form. Singlet oxygen generation is not observed when the diarylethene is converted to the closed form. Irradiation of the closed form with visible light (>470 nm) leads to full recovery of the singlet oxygen generating ability of the porphyrin sensitizer.

The authors discovered some errors regarding reference group labels in Table 2. The corrected table is attached. The authors regret these errors.

Research on photochromic molecules switched by visible light is of particular interest for their application in bioimaging and stimuli-responsive materials. Here, a photoswitchable supramolecular assembly comprised of monocharged bispyridinium-modified diarylethenes (DAEs) and cucurbit[8]uril (CB[8]) has been constructed, which exhibits reversible photochromic behaviour with visible light in both directions. The transformation of CB[8] not only prompts the DAEs to form charge-transfer complexes, but also restricts its intramolecular rotation to enhance fluorescence emission. In this CB[8]-containing supramolecular system, the π-conjugation is extended and its absorption is bathochromically shifted for visible light-driven cyclization of DAEs. Meanwhile, the fluorescence of the supramolecular assembly can also be reversibly modulated by visible light. These findings may furnish a new strategy for the development of visible light-driven fluorescent biomaterials and molecular machines.

Fluorescence and photoacoustic imaging have different advantages in cancer diagnosis; however, combining effects in one agent normally requires a trade-off as the mechanisms interfere. Here, based on rational molecular design, we introduce a smart organic nanoparticle whose absorbed excitation energy can be photo-switched to the pathway of thermal deactivation for photoacoustic imaging, or to allow opposed routes for fluorescence imaging and photodynamic therapy. The molecule is made of a dithienylethene (DTE) core with two surrounding 2-(1-(4-(1,2,2-triphenylvinyl)phenyl)ethylidene)malononitrile (TPECM) units (DTE-TPECM). The photosensitive molecule changes from a ring-closed, for photoacoustic imaging, to a ring-opened state for fluorescence and photodynamic effects upon an external light trigger. The nanoparticles' photoacoustic and fluorescence imaging properties demonstrate the advantage of the switch. The use of the nanoparticles improves the outcomes of in vivo cancer surgery using preoperative photoacoustic imaging and intraoperative fluorescent visualization/photodynamic therapy of residual tumours to ensure total tumour removal.

Herein we report the first photochromic polyoxometalate (POM)-based diarylethene (DAE) coordination complex, prepared by ligation of two cobalt(III)-incorporated borotungstates [BWOCo] with the ditopic pyridyl-containing diarylethene (CHNFS). The solution-state composition, structure, and stability of the assembly were probed using H and F nuclear magnetic resonance spectroscopy (NMR), electrospray ionization quadrupolar time-of-flight mass spectrometry (ESI-QTOF-MS), ultraviolet-visible spectroscopy (UV-vis), and small-angle X-ray scattering (SAXS), revealing that the complex self-organizes to adopt a molecular dumbbell structure due to electrostatic and steric considerations. This conformation is a prerequisite for the photocyclization reaction. The assembly was found to be switchable between two states using visible light due to the perturbation of the DAE electronic structure on coordination to the POM. We present photophysical data, including the reaction quantum efficiency of the molecular switch in both directions measured using a custom-built quantum yield determination setup in addition to fatigue resistance on prolonged irradiation.

Current development of light-responsive materials and technologies imposes an urgent demand on visible-light photoswitching on account of its mild excitation with high penetration ability and low photo-toxicity. However, complicated molecular design and laborious synthesis are often required for visible-light photoswitch, especially for diarylethenes. Worse still, a dilemma is encountered as the visible-light excitation of the diarylethene is often achieved at the expense of photochromic performances. To tackle these setbacks, we introduce a building-block design strategy to achieve all-visible-light photochromism with the triplet-sensitization mechanism. The simply designed diarylethene system is constructed by employing a sensitizer building-block with narrow singlet-triplet energy gap (ΔE) to a diarylethene building-block. A significant improvement on the photochromic efficiency is obtained as well as an enhanced photo-fatigue resistance over those under UV irradiation. The balance between the visible-light excitation and decent photochromism is thus realized, promoting a guiding principle for the visible-light photochromism.

The fast light-responsive dithienylethenes (DTEs) are one of the most attractive photochromic families because of their excellent thermal irreversibility and fatigue resistance. However, the all-visible-light-activated DTE system still remains challenging because most of them require the harmful high-energy ultraviolet light to trigger their photocyclization reaction. Here, we have for the first time borrowed a specific intramolecular proton transfer (IPT) process and rationally designed a series of all-visible-light-driven DTEs. Incorporating the IPT-functional group to DTE unit gives rise to an extra absorption band with a distinct red shift, which enables the photocyclization of DTEs under stimuli of visible light at 450 nm, as well as ensuring the desirable photoswitching efficiency. The isomerization from OH form to NH form induced by IPT can decrease the energy gap for excitation and photocyclization, thereby affording the all-visible-light-triggered photochromic performance, which can not only work well in a polar solvent system but also show its effectiveness in polymeric gel systems. In this regard, we can provide a general and reliable platform to construct all-visible-light-driven DTEs with excellent reversible photoswitching and broad applicability, especially with avoiding the use of harmful ultraviolet light to induce their photocyclization.

Operating photoswitchable molecules repetitively and reliably is crucial for most of their applications, in particular in (opto)electronic devices, and related to reversibility and fatigue resistance, which both critically depend on the photoisomerization mechanism defined by the substitution pattern. Two diarylethene photoswitches bearing biacetyl triplet sensitizers either at the periphery or at the core were investigated using both stationary as well as transient UV/Vis absorption spectroscopy ranging from the femtosecond to the microsecond time scale. The diarylethene with two biacetyl moieties at the periphery is switching predominantly from the triplet excited state, giving rise to an enhanced fatigue resistance. In contrast, the diarylethene bearing one diketone at the photoreactive inner carbon atom cyclizes from the singlet excited state and shows significantly higher quantum yields for both cyclization and cycloreversion.

Thin layers of diarylethene oligomers (oligo(DAE)) were deposited by electrochemical reduction of a diazonium salt on glassy carbon and gold electrodes. The layers were fully characterized using electrochemistry, XPS, and AFM, and switching between open and closed forms using light was evidenced. Solid-state molecular junctions (MJs), in which a C-AFM tip is used as the top contact, were fabricated with total layer thicknesses fixed at 2-3 nm and 8-9 nm, i.e. below and above the direct tunneling limit. DAE was then photoswitched between its open and closed forms. Oligo(DAE) MJs using the open form of DAE are highly resistive while those with DAE in the closed form are more conductive. ON/OFF ratios of 2-3 and 200-400 were obtained for 3-nm- and 9-nm-thick DAE MJs, respectively.