Novel 1,2-bis(2-alkylthien-3-yi)hexafluorocyclopentenes containing the alkylthio or alkylsulfonyl groups in positions 5 and 5' of the thiophene rings were synthesized. These compounds are photoehromes; their photochromic properties were studied.
No abstract
A lot of previously unknown derivatives of dithienylperfluorocyclopentene (DTPFCP) were synthesized. It was shown that 2,2′-dialkylsubstituted DTPFCP'S are phtochromes. The quantum yields of forward and backward photochemical reactions and spectral parameters of open and cyclic forms of the photochromes synthesized were measured. An attempt to obtain fluorescing phtochromes by means of introduction of benzoxazolyl, benzthiazolyl and 1,2,4-oxadiazolyl moieties in 5 and 5′ positions of DTPFCP failed; these compounds were synthesized but they do not fluoresce
The structures of two hetarytethene photochromes, viz., 1.2-bis(2-ethyl-5ethylsulfonylthien-3-yl)perfluorocyclopentene and 1.2-bis[5-(benzoxazol-2-yl)-2-methylthien-3-yllperfluorocyclopentene, were established by X-ray diffraction analysis. The conformational parameters of the title compounds are considered. The cyclopentene ring in the former compound is planar and this ring in the latter compound adopts an envelope conformation. There are no overall conjugated systems in the molecules under study. In both structures, the dihetaryl fragments are rotated with respect to the perfluorocyclopentene fragments by -55 ~ The thiophene and benzoxazole rings in 1.2-bisl5-(benzoxazol-2-yl)-2-methylthien-3yljperfluorocyclopentene are coplanar.
The synthesis of 1,2-bis(2-ethylthio-3-thienyl)perfluorocyclopentene is described. Metallation with n-BuLi and subsequent treatment with DMF or CO 2 gave the corresponding 5,5'-diformyl and dicarboxy derivatives. The structure of 1, 2-bis(2-etbylthio-3-thienyl) Compounds containing diaryl-or diheteryl(dithienyl)alkene fragments, potentially capable of valence tautomerism, are widely used to obtain organic materials applicable in information technics and optoelectronics [1]. A characteristic of such materials is. the possibility of a wide variation in physicochemical and photochromic properties with even small changes in molecular structure. For example, replacement of methyl groups by n-hexyl in positions 2 of the thiophene rings in compounds of type A not only increases the solubility in certain organic solvents 30 fold but also shifts the absorption maximum in the electronic spectrum by 20-30 nm [2]. A change in the nature of the substituent at position 5 of the thiophene ring proved to have a significant effect on the photochromic properties and thermal stability of one of the tautomeric forms [3, 4]. The effect of the nature of the substituent at positions 2 of the thiophene rings in similar systems has not been studied. RI~R 1A hv RI~R 1 B R = Me, R t = CLIO, Ar, HetIn the present work derivatives have been obtained for the first time of 1,2-bis(thienyl)perfluorocyclopentene (I) containing an alkylthio group in position 2 of the thiophene ring. This activates the thiophene ring in electrophilic substitution and metallation reactions, facilitating the subsequent introduction of various functional substituents into the free positions of the heterocycle.Compound (I) was synthesized from 2-ethylthiophene according to the scheme shown below. Bromination of the latter and subsequent debromination of the obtained dibromosulfide flI) with n-BuLi at -70~ leads to 3-bromo-2-ethylthiothiophene (III) in good yield. The bisulfide (I) was synthesized in 60% yield by the successive action on bromide (III) of BuLi in ether and then octafluorocyclopentene. Compound (I) was converted practically quantitatively by an excess of 30% H202 into the bisulfone (IV). The bisulfide (I) is metallated in both of the thiophene rings in a few minutes with BuLi in ether and after treatment with DMF or CO 2 is converted in good yield into the dialdehyde (V) or the dicarboxylic acid (VI) respectively. Metallation of the alkyl analog 1,2-bis(2-hexyl-3-thienyl)perfluorocyclopentene proceeds with significantly more difficulty and requires the use of TMEDA [2].
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