Dithienylethene

Photoinduced transformations of photochromes (spiropyrans, furan-derived fulgides, dithienylethenes) in polymers 98PAC2157. 

Hellmann, J., Hamano, M., Karthaus, O., Ijiro, K., Shimomura, M. and Irie, M. (1998) Aggregation of dendrimers with a photochromic dithienylethene core group on the mica surface - atomic force microscopic imaging. Jpn. J. Appl. Phys., 37, L816-L819. 

Higashiguchi K, Matsuda K, Asano Y, Murakami A, Nakamura S, Irie M (2005) Photochro-mism of dithienylethenes containing fluorinated thiophene rings. Eur J Org Chem 91-97... 

Other dithienylethenes have been synthesized and investigated for their photo-chromic properties by replacing the fc/V-butyl group by bis(p-methylphenyl) amine, thus raising the glass transition temperatures [293, 294]. 

The terms diarylethenes, dithienylethenes, and dihetarylethenes, as applied to the structures of photochromic products II, of course, do not strictly meet the nomenclature requirements. However, these terms have gained wide acceptance in the special literature. The classification of compounds containing heterocycles as bridges is also rather arbitrary. 

An alternative method for dithienylperfluorocyclopentenes is based on the functionalization of the presynthesized dithienylethenes having, as a rule, very simple structures. Scheme 4 shows a part of the synthetic route (the assembly of unique photochrome 7 performed by Lehn and coworkers) by a Suzuki reaction starting from available boronic acids 6 (96CEJ1399). This reaction is widely used for the modification of the dihe-tarylethene moiety by aromatic substituents. This scheme also gives the reverse example of the synthesis of 9, where the boronic acid fragment is present in 8 (07JPP(A)202). 

A successive increase in the chain length in dithienylethene 6 by a Suzuki reaction leads to the formation of polythienyl photochromes 10 (Scheme 5). 

More recently, dithienylethenes 64 containing the (4-pyridyl)ethyl and (4-pyridyl)ethynyl groups at position 2 of the thiophene ring (080L2051) have been synthesized in a similar way. Photochrome 65 was prepared from 2-hydroxymethylbenzo[b]thiophene according to Scheme 19 (05IZV2697). 

In 09NJC1320, an original method was developed for the preparation of fluorescent photochrome 112, which contains both electron-donating and electron-withdrawing groups and bipyridine-bridged dithienylethene fragments, from 110 with bisphosphonate bipyridine 111 in the presence of a base (Scheme 36). 

The synthesis of dithienylethenes bound to heteroanalogs of cyclopentene, in particular to the 2,5-dihydrothiophene ring, also deserves notice. Diketone 135 was prepared by the replacement of the bromine atoms in two molecules of 134 by the sulfide anion followed by the McMurry cyclization to form thiacyclopentene derivative 136 (03OL1435). Diiodide 137 is also successfully used as the synthon for the subsequent functionalization this compound is involved in the Suzuki reaction to... 

The study (05ZOR89) showed that thenoines actively react with thiols in acidic media at room temperature to give /1-keto sulfides 250 in good yields. On alkaline hydrolysis, the latter compounds are readily cleaved to ketones 251, which are valuable intermediates for subsequent syntheses. In 06MI2, they were involved in a Fischer reaction and indole- bridged dithienylethenes 252 and 253 were obtained. Hence, a convenient procedure was developed for the transformation of readily available acyloins into photochromic indole-bridged dithienylethenes (Scheme 71). 

Volume 103 of our series contains three substantial chapters. M.M. Krayushkin and M.A. Kalik (affiliated with Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow) summarize synthetic work directed to photochromic dihetarylethenes. Work has been especially concentrated on dithienylethenes that have considerable potential derived from photochemically induced isomerizations between the cis-and trans-forms and cyclized derivatives. 

A number of photochromic systems have been extensively investigated that undergo cis-trans isomerization (indigos, azo compounds) cleavage (spiropyrans), electrocyclic processes (fulgides, 1,2-diarylethenes) [8.229, 8.244, 8.245], For instance, cis-trans isomerization of a thio-indigo derivative allows the reading of pyrene excimer or monomer fluorescence [8.246]. The 1,2-dithienylethene system presents particularly attractive interconversion properties by photoreversible cyc-litation [8.245],... 

Substituents on the reactive position greatly influence the photoreactivity. 2-Thienyl derivatives have been reported to work very well (03JA3404). The control of the photoreactivity by external stimuli such as pH or electric potential is important for the practical application of diarylethenes, because a controlled photoreactivity, namely a gated reactivity, can provide a nondestructive readout capability. Pyridyl group is one of the external stimuli-responsive substituents that are quaternized by alkylating reagent or protic acid. Dithienylethene derivatives 250-253 have been reported. 

Dithienylethene derivatives bearing a phthalimido group 259 have been studied (08EJO2531). The open form absorbs at 370 nm and irradiation at 313 nm resulted in a rapid appearance of the characteristic absorption band of the closed form 260 at 573 nm. 

Dithienylethene derivatives can also be linked to a fluorescent bisfphe-nylethynyl)-anthracene residue, showing that the irradiation at 313 ran, able to give the closed form of the photochromic device, the fluorescence of the anthracene moiety at 530 nm is efficiently quenched (Of < 0.001) (01JCS(CC)711). 

UV irradiation of the dithienylethene complexes 275-279 caused ring closure to form the purple- or deep-blue-colored closed isomer showing... 

Photochromism has also been observed when two porphyrinic groups are linked to a dithienylethene scaffold. The closed form showed an absorption band at 560 nm (01JA1784). The same behavior was observed in the system 318-319 (02AM918). Dithienylethene photochromic systems have also been described to be linked to single-walled nanotubes (07JA12590). 

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