A chiral photoswitch based on enantiospecific interconversion between binaphthyl and helicenoid skeletons.

A novel chiral photoswitch composed of a binaphthyl unit and a hexafluorocyclopentene ring has been synthesized. This chiral photoswitch exhibited thermally reversible photochromism between the binaphthyl and helicenoid forms based on 6π-electrocyclization. The helicity of the binaphthyl moiety was reversed upon stereospecific photocyclization and reverted back during the thermal ring opening.

Ion valence-gated photochromism of an aza-crowned diarylethene.

A non-photochromic diarylethene 2o with an N-phenylaza-15-crown-5 was synthesized. When the nitrogen atom in the aza-crown ring was protonated, it became photochromic due to the prevention of a twisted intramolecular charge transfer (TICT). Although addition of a monovalent metal cation (Li+, Na+, K+, Rb+, Cs+, Cu+, Ag+) in acetonitrile could not stop the TICT so that it was not photochromic, the addition of a multivalent metal cation (Mg2+, Ca2+, Sr2+, Ba2+, Fe2+, Ni2+, Al3+, Sb5+) changed 2o to be photochromic due to the strong attraction of the lone pair on the nitrogen atom. In the presence of excess Cu2+, 2o was oxidized to be EPR-detectable 2o·+, which was thermally unstable as well as inert towards visible-light irradiation. However, 2o·+ was further oxidized to be fairly stable 2o2+ by the irradiation of 365-nm light in the presence of Cu2+. ESI-MS measurements strongly suggested the generation of 2o·+ by mixing 2o with Cu(ClO4)2 in acetonitrile, and the transformation of 2o·+ to 2o2+ by successive 365-nm light irradiation. Fe3+ similarly worked as the oxidant, but the two-step oxidation of 2o to 2o2+ occurred more easily.

On-Demand Chirality Transfer of Human Serum Albumin to Bis(thiophen-2-yl)hexafluorocyclopentenes through Their Photochromic Ring Closure.

Photochromic 1,2-bis(5-carboxy-3-methyl-2-thienyl)hexafluorocyclopentene and its dimethyl ester incorporated in human serum albumin (HSA) showed highly enantioselective photochromic ring-closing reactions upon 366 nm light irradiation. The absolute stereochemistry of the major ring-closed form of the dicarboxylic acid at the newly formed sp3 carbon atoms was determined to be (S,S) by the process of docking simulation of the diarylethene molecule and HSA followed by molecular dynamics calculations and comparison of the measured and calculated CD spectra. Esterification of the major closed form of the diacid gave the minor closed form of the diester. The absolute stereochemistry of the major diester was thus determined to be (R,R).

Chiral, Thermally Irreversible and Quasi-Stealth Photochromic Dopant to Control Selective Reflection Wavelength of Cholesteric Liquid Crystal.

The front cover artwork is provided by the group of Prof. Emeritus Yasushi Yokoyama and Prof. Takashi Ubukata. The image shows the generation of a colored image, whose origin is the UV-controlled selective reflection of visible light from a cholesteric liquid crystal containing chiral photochromic molecules. Read the full text of the Article at 10.1002/cphc.202000309.

Chiral, Thermally Irreversible and Quasi-Stealth Photochromic Dopant to Control Selective Reflection Wavelength of Cholesteric Liquid Crystal.

A chiral and thermally irreversible photochromic fulgide derivative incorporating an (R)-binaphthol unit in its acid anhydride moiety was used for the photoswitching of the pitch length of cholesteric liquid crystals. Since the absorption maximum wavelengths of both thermally stable photoisomers are nearly in the UV region (quasi-stealth photochromism), it can be exposed to visible light without inducing photochromic reactions. Therefore, when the photoswitching molecule is added to a permanent cholesteric liquid crystal whose reflection light wavelength is in the visible region, the UV light-induced photochromic reaction of the photoswitching molecule changes the wavelength of the reflection light in the visible light region. We have succeeded in regulating the color of cholesteric liquid crystalline cells between red and blue upon UV light irradiation. Attempts to introduce this system in polymer dispersed cholesteric liquid crystals are also described.

A thermoresponsive fluorophore based on a photochromic diarylethene having donor-acceptor moieties.

A thermoresponsive fluorophore based on a photochromic diarylethene possessing donor and acceptor moieties in close proximity to each other has been synthesized. The fluorophore exhibits dual fluorescence, where photoresponsive turn-off switching as well as a thermoresponsive relative intensity change are observed.

Post-Modification of the Ethene Bridge in the Rational Design of Photochromic Diarylethenes.

Fine-tuning of the molecular structure of organic bistable compounds to improve their photochromic performance or to introduce additional functions remains an important issue in the development of photoresponsive materials. Diarylethenes bearing heterocyclic moieties belong to the most intensively studied class of organic photochromes due to their excellent photochemical properties. A huge number of diarylethenes have been synthesized so far. Analysis of the literature data shows that there are very worthy examples of diarylethenes developed by the Irie and Feringa groups, which can be the common starting material for a number of diarylethenes functionalized in hetaryl moieties. We refer to these structures as photochromic diarylethene precursors. These diarylethenes have proved to be very useful in the construction of functional molecules with desired properties. On the other hand, in our groups, we have elaborated on diarylethene precursors with modifiable ethene bridges. In this review, we have collected examples of such structures and their chemical modifications, leading to the improvement or fine-tuning of photochromic switching.

Click chemistry towards thermally reversible photochromic 4,5-bisthiazolyl-1,2,3-triazoles.

Three new diarylethenes were synthesized from 1,2-bis(5-methyl-2-(4-substituted-phenyl)thiazol-4-yl)ethyne and benzyl azide through Ru(I)-catalyzed Huisgen cyclization reactions. The 4,5-bisthiazolyl-1,2,3-triazoles thus prepared, which belong to the terarylene family, showed thermally reversible photochromism. The absorption maximum wavelengths of the closed forms are longer than other terarylenes reported so far. The thermal back reactions are much faster when the substituents on the terminal phenyl groups are electron-withdrawing cyano groups than when they are electron-donating methoxy groups.

One-Step Synthesis and Stealth Photochromism of Arylbutadienes.

The synthesis of thermally irreversible photochromic arylbutadienes has been demonstrated with a one-step reaction using commercially available ketones by McMurry cross-coupling. Although ( Z)-5-(1-([1,1'-bi(cyclopentylidene)]-2-ylidene)ethyl)-4-methyl-2-phenylthiazole, a 1-(4-methyl-2-phenyl-5-thiazolyl)butadiene, showed poor photochromism, ( Z)-5-(1-([1,1'-bi(cyclopentylidene)]-2-ylidene)ethyl)-2,4-dimethylthiazole, a 1-(2,4-dimethyl-5-thiazolyl)butadiene, showed stealth photochromic transformations by 313 and 366 nm light irradiation between the moderate conversion ratios of the open and closed forms.

Photochromism and the fluorescence properties of bisbenzothienylethene and S,S,S',S'-tetraoxide derivatives with dual conjugated fluorescent groups on their side chains.

Two photochromic bisbenzothienylethenes with two fluorescent (4-((2,5-bis(dodecyloxy)-4-(phenylethynyl)phenyl)ethynyl)phenyl) units and their disulfone derivatives were synthesized, and their photochromic and fluorescence properties were examined. Bisbenzothienylethenes showed photochromism and turn-off type fluorescence by UV-light irradiation, while their disulfone derivatives showed turn-on type fluorescence and the one-way isomerization to the closed form.

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-colour fluorescence modulation with a photon-quantitative photocyclization reactivity and high thermal stability.

Photocyclization of photoswitches with high enantioselectivity in human serum albumin in an artificial environment.

Three photochromic bisthienylethenes exhibited 56 to >99% enantiomeric excess in photochemical ring closure upon UV irradiation when incorporated in human serum albumin dissolved in 15% acetonitrile-phosphate buffer solution and incubated for 24 h at -4 °C. The absolute stereochemistry of the major enantiomers of two bisthienylethenes has been determined by their chemical transformations.

Gated Photochromic System of Diarylethene with a Photon-Working Key.

Upon visible light irradiation, a thermally reversible photochromic acid generator merocyanine dye gives a proton to the dimethylamino group of a non-photochromic diarylethene in acetonitrile. The protonation rendered the non-photochromic diarylethene photochromic. Thus, the thermally irreversible photochromic nature of the diarylethene is activated without any physical contact or addition of any compound but only by photoirradiation to the merocyanine dye.

Highly Sensitive Formation of Stable Surface Relief Structures in Bisanthracene Films with Spatially Patterned Photopolymerization.

A facile method for the fabrication of a highly sensitive surface relief is demonstrated, which operates on the principle of spatially patterned photopolymerization-induced mass transport in the amorphous films of a series of bisanthracene compounds. The stability of the resultant colorless transparent relief structure is dramatically improved owing to the polymerization of the bisanthracene.

A photon-working on/off switch for intramolecular donor-acceptor interactions and invisible modulation of the fluorescence.

An on/off switching for charge-transfer interactions between the side chains of a diarylethene based on photochromic reactions has been proved by the disappearance and appearance of an additional fluorescence band.

Bisarylindenols: fixation of conformation leads to exceptional properties of photochromism based on 6π-electrocyclization.

Thermally irreversible photochromic 1-tert-butyl-substituted 2,3-bisthiazolylindenol has been synthesized. It showed perfect diastereoselectivity and high ring-closing quantum yield with high conversion ratio to the closed form. The collaborative interaction of two intramolecular hydrogen bonds and the steric restriction fixed the conformation in favour of cyclization in a highly diastereoselective manner.

Photochromic C2-symmetric chiral diarylethene: from the initial state to the final state.

The behavior of 1,2-bis[(R)-2-(1-methoxymethoxyethyl)-3-benzo[b]thienyl] hexafluorocyclopentene before and upon UV irradiation and during thermal evolution of the photoirradiated solution has been thoroughly investigated by multinuclear NMR spectroscopy. A dynamic NMR study of the initial state was performed, providing a detailed description of the perceived conformational processes in the system. Before irradiation, three open conformations are in equilibrium, whereas UV irradiation generated the two expected cyclized diastereomers. The minor diastereomer was thermally less stable than the major one, thus leading to an unexpected increase in the diastereoselectivity when raising the photoirradiation temperature. In addition, a long thermal evolution induced slow rearrangement of the stable diastereomer into byproducts that were identified.

Dual-mode fluorescence switching of photochromic bisthiazolylcoumarin.

Three new photochromic coumarins were synthesized. Fluorescence of the open form of 7-hydroxy-3,4-bisthiazolyl-coumarin increased to 1400% by changing the pH only slightly from 6.05 to 7.58. This was subsequently quenched to 1.5% of the maximum intensity at the UV photostationary state in water-methanol media.

Ultimate diastereoselectivity in the ring closure of photochromic diarylethene possessing facial chirality.

A bisthienylethene with hitherto unprecedented facial chirality imposed by a triethyleneglycol bridge on a thiophene ring was synthesized and its photochromic ring closure was shown to occur with 100% diastereoselectivity upon UV-light irradiation.