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.

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.

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.

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.

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.

Photoinduced diffusive mass transfer in o-Cl-HABI amorphous thin films.

The first demonstration of photoinduced surface relief grating formation using amorphous thin films composed of a radical dissociative photochromic compound, 2,2'-di(ortho-chlorophenyl)-4,4',5,5'-tetraphenylbiimidazole, show that mass transfer occurred from the UV-light-irradiated area to the shaded area by patterned light irradiation (365 nm).

Fast decoloration of spironaphthooxazine bound to a poly(dimethylsiloxane) network.

Spironaphthooxazine (SNO) was attached to a three-dimensional network of polysiloxane through the allyloxy group on C-7 of the naphthalene ring of SNO, and the photochemical coloration and thermal decoloration behaviors of this material (Film-P) were examined by comparing their properties with those of model SNO having a 7-propyloxynaphthyl group in solution, in a doped polysiloxane film (Film-D), and in a doped PMMA film. For Film-P, the SNO units were connected to a part of the vinyl groups on the Si atoms of a linear polysiloxane by hydrosilylation, and the remaining vinyl groups were bridged by the bifunctional linear polysiloxane possessing two hydrosilyl groups at both ends of the chain. While Film-P containing 1.7 x 10(-3) mol dm(-3) of the SNO unit formed a transparent film, Film-D containing more than 1.2 x 10(-3) mol dm(-3) could not form a transparent film but segregation of SNO occurred. A transparent Film-D was prepared at 0.54 x 10(-3) mol dm(-3) SNO concentration. The decoloration reaction rate of Film-D was faster than those for Film-P, solutions, and PMMA. However, due to the low concentration, the coloration of Film-D was weak. When the concentration of SNO in Film-P was increased 5.7 times, the decoloration rate became 3.6 times faster. Its half-life time was 0.9 s, which is 3.1 times as fast as that of corresponding solution in hexamethyldisiloxane.

Structurally versatile novel photochromic bisarylindenone and its acetal: achievement of large cyclization quantum yield.

Bisarylindenones and an acetal derivative, a novel thermally irreversible photochromic family based on 6pi-electrocyclization with three easily modifiable functional groups, have been synthesized. 2,3-Bis(5-methyl-2-phenyl-4-thiazolyl)indenone showed photochromic back-and-forth reactions with two different visible lights. Its ethylene acetal recorded 0.81 as the photocyclization quantum yield in hexane, which is the largest value known to date for 6pi-electrocyclization in solution.

A unified strategy for exceptionally high diastereoselectivity in the photochemical ring closure of chiral diarylethenes.

Into my arms: Photochemical cyclization of diarylethenes that have two chiral side arms showed up to 100% de (see scheme). Introduction of these chiral side arms onto the carbon atoms where ring closure occurs is a general strategy for the highly diastereoselective cyclization of diarylethenes.

Dendrimer diarylethenes: the memory effect of conformation in polymer matrices.

Photochromic dendrimer diarylethenes with a C-2-connected bisbenzothienylethene core were synthesized; the most notable feature of them is the strong memory effect of cyclizable conformation of the open form when generated from the closed form by visible light irradiation in polycarbonate films.

Chiral helicenoid diarylethene with highly diastereoselective photocyclization.

A novel photochromic helicenoid diarylethene (R)-1-[1-(1-methoxymethoxyethyl)-2-naphtho[2,1-b]thienyl]-2-(2,4,5-trimethyl-3-thienyl)hexafluorocyclopentene was synthesized enantioselectively. It showed highly diastereoselective photocyclization (90% de) and a large change (950 degrees) in the specific optical rotation value at 633 nm upon UV light irradiation in ethyl acetate.