Separation of Photoactive Conformers Based on Hindered Diarylethenes: Efficient Modulation in Photocyclization Quantum Yields

New insights into the photoswitching mechanisms of normal dithienylethenes

The photoswitching and competitive processes of the referent photochromic diarylethene derivative 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene (DTE) and a novel bridged analog DTE-m5 have been investigated by state-of-the-art TD-DFT calculations and ultrafast spectroscopy supported by advanced chemometric data treatments. Focusing on DTE, the overall deactivation pathway of both antiparallel (AP) and parallel (P) conformers of the open form (OF) (1 : 1 in solution) has been resolved and rationalized starting from the Franck-Condon (FC) region to the ground state recovery. For the photo-excited P conformer, after ultrafast relaxation (∼200 fs) towards the S₁ relaxed state, an expected ISC occurred (55 ps) to produce a triplet state, ³P, the latter relaxing within 2.5 μs. Concerning the AP conformer, the photocyclization reaction is reported to proceed immediately (100 fs) starting from the FC region while the relaxed singlet state is populated in parallel. For the first time, we discovered that the latter state evolves through an unexpected ISC process (1 ps) giving rise to a second triplet state,³AP. For DTE-m5, by slightly constraining the molecule with the bridge, this triplet becomes reactive and participates in the formation of 10% of closed form (CF) probably through an adiabatic mechanism. Concerning the photoreversion, in accordance with the literature, we report on a two-step process, a 190 fs vibrational relaxation followed by a 6 ps ring-opening reaction. For the overall species at the singlet or triplet manifold, the use of advanced MCR-ALS allows us to obtain specific spectral signatures. This study is therefore a new step within the comprehension of DTE photochemistry.

Photochromism of a spiro-functionalized diarylethene derivative: multi-colour fluorescence modulation with a photon-quantitative photocyclization reactivity

A spiro-functionalized photochromic diarylethene derivative showed multi-color fluorescence modulation with a photon-quantitative photocyclization reactivity.

Boolean Logic Tree of Label-Free Dual-Signal Electrochemical Aptasensor System for Biosensing, Three-State Logic Computation, and Keypad Lock Security Operation

The most serious and yet unsolved problems of molecular logic computing consist in how to connect molecular events in complex systems into a usable device with specific functions and how to selectively control branchy logic processes from the cascading logic systems. This report demonstrates that a Boolean logic tree is utilized to organize and connect "plug and play" chemical events DNA, nanomaterials, organic dye, biomolecule, and denaturant for developing the dual-signal electrochemical evolution aptasensor system with good resettability for amplification detection of thrombin, controllable and selectable three-state logic computation, and keypad lock security operation. The aptasensor system combines the merits of DNA-functionalized nanoamplification architecture and simple dual-signal electroactive dye brilliant cresyl blue for sensitive and selective detection of thrombin with a wide linear response range of 0.02-100 nM and a detection limit of 1.92 pM. By using these aforementioned chemical events as inputs and the differential pulse voltammetry current changes at different voltages as dual outputs, a resettable three-input biomolecular keypad lock based on sequential logic is established. Moreover, the first example of controllable and selectable three-state molecular logic computation with active-high and active-low logic functions can be implemented and allows the output ports to assume a high impediment or nothing (Z) state in addition to the 0 and 1 logic levels, effectively controlling subsequent branchy logic computation processes. Our approach is helpful in developing the advanced controllable and selectable logic computing and sensing system in large-scale integration circuits for application in biomedical engineering, intelligent sensing, and control.

Light-Controlled Reversible Modulation of Frontier Molecular Orbital Energy Levels in Trifluoromethylated Diarylethenes

Among bistable photochromic molecules, diarylethenes (DAEs) possess the distinct feature that upon photoisomerization they undergo a large modulation of their π-electronic system, accompanied by a marked shift of the HOMO/LUMO energies and hence oxidation/reduction potentials. The electronic modulation can be utilized to remote-control charge- as well as energy-transfer processes and it can be transduced to functional entities adjacent to the DAE core, thereby regulating their properties. In order to exploit such photoswitchable systems it is important to precisely adjust the absolute position of their HOMO and LUMO levels and to maximize the extent of the photoinduced shifts of these energy levels. Here, we present a comprehensive study detailing how variation of the substitution pattern of DAE compounds, in particular using strongly electron-accepting and chemically stable trifluoromethyl groups either in the periphery or at the reactive carbon atoms, allows for the precise tuning of frontier molecular orbital levels over a broad energy range and the generation of photoinduced shifts of more than 1 eV. Furthermore, the effect of different DAE architectures on the transduction of these shifts to an adjacent functional group is discussed. Whereas substitution in the periphery of the DAE motif has only minor implications on the photochemistry, trifluoromethylation at the reactive carbon atoms strongly disturbs the isomerization efficiency. However, this can be overcome by using a nonsymmetrical substitution pattern or by combination with donor groups, rendering the resulting photoswitches attractive candidates for the construction of remote-controlled functional systems.

Photochromic benzo[b]phosphole oxide with excellent thermal irreversibility and fatigue resistance in the thin film solid state via direct attachment of dithienyl units to the weakly aromatic heterocycle

A novel photochromic benzo[b]phosphole oxide has been demonstrated to display photochromic properties with excellent fatigue resistance and thermal irreversibility in polymethylmethacrylate (PMMA) thin film under ambient conditions. The remarkable photochromic behaviour can be achieved by rational molecular design, in which the weakly aromatic phosphole oxide is directly incorporated into the photo-responsive dithienylethene units. Photopatterning via photoinduced colouration and decolouration has been performed to demonstrate the repeatable and distinct transformation between the bistable states, making it a promising candidate with photoswitching properties for optoelectronic applications.

A fluorescent photochromic diarylethene based on naphthalic anhydride with strong solvatochromism

A diarylethene molecule consisting of an 1,8-naphthalic anhydride and two 2,5 dimethylthiophene which exhibits reversible fluorescence switching capacity as well as solvatochromism with red shift of the fluorescence maximum by more than 150 nm.

Two rare meroterpenoidal rotamers from Ganoderma applanatum

Applanatumols Z3 (1) and Z4 (2), two novel natural product hybrids consisting of a meroterpenoid and a glycerol and three known compounds (3–5) were isolated from the fruiting bodies of the fungus Ganoderma applanatum.

Structure and photochromism of 1-(1,2-dimethylindol-3-yl)-2-[2-methyl-5-(3-fluorophenyl)-3-thienyl]-3,3,4,4,5,5-hexafluorocyclopent-1-ene, C26H18F7NS

C26H18F7NS, triclinic, P1̅, a = 8.492(18) Å, b = 11.23(2) Å, c = 14.75(3) Å, α = 68.93(2)°, β = 74.90(2)°, γ = 68.35(2)°, V = 1206(4) Å3, Z = 2, R gt(F) = 0.0511, wR ref(F 2) = 0.1643, T = 296(2) K.

Extending human perception of electromagnetic radiation to the UV region through biologically inspired photochromic fuzzy logic (BIPFUL) systems

Photochromic fuzzy logic systems have been designed that extend human visual perception into the UV region. The systems are founded on a detailed knowledge of the activation wavelengths and quantum yields of a series of thermally reversible photochromic compounds. By appropriate matching of the photochromic behaviour unique colour signatures are generated in response differing UV activation frequencies.

Enabling Light Work in Helical Self-Assembly for Dynamic Amplification of Chirality with Photoreversibility

Light-driven transcription and replication are always subordinate to a delicate chirality transfer. Enabling light work in construction of the helical self-assembly with reversible chiral transformation becomes attractive. Herein we demonstrate that a helical hydrogen-bonded self-assembly is reversibly photoswitched between photochromic open and closed forms upon irradiation with alternative UV and visible light, in which molecular chirality is amplified with the formation of helixes at supramolecular level. The characteristics in these superhelixes such as left-handed or right-handed twist and helical length, height, and pitch are revealed by SEM and AFM. The helical photoswitchable nanostructure provides an easily accessible route to an unprecedented photoreversible modulation in morphology, fluorescence, and helicity, with precise assembly/disassembly architectures similar to biological systems such as protein and DNA.

Stereoselective photoreaction in P-stereogenic dithiazolylbenzo[b]phosphole chalcogenides

The diastereoselective photoreaction of dithiazolylbenzo[b]phosphole chalcogenides was achieved by means of the conformational control of the photoprecursor state by intramolecular interactions involving the stereogenic phosphorus.

Photoswitchable fluorescent nanoparticles and their emerging applications

Although fluorescence offers ultrasensitivity, real-world applications of fluorescence techniques encounter many practical problems. As a noninvasive means to investigate biomolecular mechanisms, pathways, and regulations in living cells, the intrinsic heterogeneity and inherent complexity of biological samples always generates optical interferences such as autofluorescence. Therefore, innovative fluorescence technologies are needed to enhance measurement reliability while not compromising sensitivity. In this review, we present current strategies that use photoswitchable nanoparticles to address these real-world challenges. The unique feature in these photoswitchable nanoparticles is that fundamental molecular photoswitches are playing the critical role of fluorescence modulation rather than traditional methods like modulating the light source. As a result, new innovative technologies that have recently emerged include super-resolution imaging, frequency-domain imaging, antiphase dual-color correlation, etc. Some of these methods improve imaging resolution down to the nanometer level, while others boost the detection sensitivity by orders of magnitude and confirm the nanoparticle probes unambiguously. These enhancements, which are not possible with non-photoswitching molecular probes, are the central topics of this review.

Enantiospecific photoresponse of sterically hindered diarylethenes for chiroptical switches and photomemories

Light-driven transcription, replication and enzyme catalysis are critically dependent upon a delicate transfer between molecular and supramolecular chirality. Chemists have well realized the impressive stereospecificity over many thermally accessible cycloaddition with chiral catalysts, but making light work in the enantiomer control of diarylethene photocyclization has proved to be more challenging. Here, we report a unique sterically hindered diarylethene (BBTE) system with absolute enantiospecific photocyclization and cycloreversion. Moreover, we have fully separated all the five thermally stable isomers, consisting of one achiral parallel conformer, one pair of anti-parallel ring-open enantiomers, and another pair of ring-closed enantiomers, whose absolute chiral configurations are entirely elucidated by single X-ray crystallographic analyses. The photo-responsive feature exhibits a reversible, complete enantio-control transformation without racemism, offering an unrivaled unimolecular enantiospecific platform for potential applications as bistable chiroptical switches and all-photonic photomemories with optical rotation as non-destructive readout.

Surface-induced selection during in situ photoswitching at the solid/liquid interface

Here we report for the first time a submolecularly resolved scanning tunneling microscopy (STM) study at the solid/liquid interface of the in situ reversible interconversion between two isomers of a diarylethene photoswitch, that is, open and closed form, self-assembled on a graphite surface. Prolonged irradiation with UV light led to the in situ irreversible formation of another isomer as by-product of the reaction, which due to its preferential physisorption accumulates at the surface. By making use of a simple yet powerful thermodynamic model we provide a quantitative description for the observed surface-induced selection of one isomeric form.

Photoswitching of triplet–triplet annihilation upconversion showing large emission shifts using a photochromic fluorescent dithienylethene-Bodipy triad as a triplet acceptor/emitter

A dithienylethene-Bodipy triad was used as a photoswitchable triplet acceptor/emitter for photoswitching of triplet–triplet annihilation upconversion with large emission wavelength changes.

CB[8] gated photochromism of a diarylethene derivative containing thiazole orange groups

Photochromism in a diarylethene derivative (1O) can be gated by a host–guest interaction where the thiazole orange groups are bound into the hydrophobic cavity of CB[8] in water.

The triplet excited state of Bodipy: formation, modulation and application

The accessing of the triplet excited state of one of the most popular fluorophores, boron-dipyrromethene (Bodipy), was summarized.

Diarylethene based fluorescent switchable probes for the detection of amyloid-β pathology in Alzheimer's disease

Two fluorescent switchable diarylethene derivatives which can detect amyloid-β aggregates bothin vitroandin vivowere reported.

Substitution effect on the photochromic properties of benzo[b]thiophene-1,1-dioxide based diarylethenes

Benzo[b]thiophene-1,1-dioxide based diarylethenes containing methyl, phenyl, formyl and triphenylamine groups are developed for taking insight into substituent effects on the absorption properties and photochromism.

Chromo-pharmacophores: photochromic diarylmaleimide inhibitors for sirtuins

Controlling the activity of sirtuins is of high biomedical relevance as the enzymes are involved in cancer, neurodegeneration and other diseases.

The photochemistry of inverse dithienylethene switches understood

The photophysical properties of a series of dithienylethenes, free or blocked in an ideal photoactive conformation by an alkyl bridge, are investigated by stationary, ultrafast spectroscopy and state-of-the-art time-dependent density functional theory calculations.