Synthesis, structure and photochromic properties of indoline spiropyrans with electron-withdrawing substituentsстатья
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Дата последнего поиска статьи во внешних источниках: 3 февраля 2022 г.
Аннотация:Indoline spiropyrans containing conjugated cationic vinyl-3H-indolium fragment and their analogues withformyl substituent in the 2H-chromene moiety were synthesized by a simple one-pot method. The structureof the obtained compounds was confirmed by 1H and 13C NMR (including 2D methods) and IR spectroscopy,as well as by element analysis and HRMS. Molecular structures of 1,3,3,6´-tetramethyl-8´-formylspiro[indoline-2,2´-2H-chromene] 8 and its cationic derivative 5 were refined by single crystal X-ray andcompared. Notably, it was found that the crystals of formyl-substituted spiropyran contain both enantiomers(R- and S-) of the molecule in the unit cell. Photochromic properties of all the compounds werestudied and compared using spectral-photokinetic methods. It was found out that electron-withdrawingsubstituents (vinyl-3H-indolium fragment and formyl group) located at the position 6of´ 2H-chromenemoiety stabilize merocyanine isomer more effectively, than at the position 8´, leading even to the appearanceof negative photochromism for the compound 3 with cationic substituent, which is quite unusualfor this class of organic photochromes. Also, it was shown that chlorine atoms as σ-acceptors at thepositions 5 and 5´of´ hetarene moiety and cationic fragment can suppress photochromic behavior