Photokinetics of two novel photochromic diarylethenes derived from benzothiophene

Abstract

Two new unsymmetrically substituted photochromic diarylethenes, namely 3- [3, 3,4,4,5,5-hexafluoro-2-(2-methylbenzothien-3-yl)cyclopent-1-en-1-yl]-2-methyl-6-methoxy-1benzothiophene and 3-[3,3,4,4,5,5-hexafluoro-2-(2-methylbenzothien-3-yl)cyclopent-1-en-1yl]-2-methyl-6-methoxy-7-nitro-1-benzothiophene, were synthesized. Their optical properties and kinetics of cyclization and cycloreversion were determined in four solvents and compared with the symmetrical diarylethene (3,3,4,4,5,5-hexafluorocyclopent-1-en-1,2-diyl)bis(2-methyl-1-benzothiophene). While the UV spectra of the three compounds are almost insensitive to solvent changes, the rates of the ring-opening and ring-closure reactions exhibit interesting kinetic behavior that differs from other diarylethenes reported in the literature. The cycloreversion for the three compounds follows first-order kinetics, whereas the cyclization cannot be described by a simple kinetic law. Different approaches were tested, and a complex exponential equation could be derived that fits the experimental data. The unusual presence of two ring-opened conformational isomers, one of them nonphotochromic, is proposed for the ring-opened compounds to explain the derived kinetic law and observed solvent effects. These results are of interest in relation to the application of the novel diarylethenes as potential optical materials. C 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: [736][737][738][739][740][741][742][743][744] 2012

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Ring opening/closure reactions of novel diheteroarylethenes derivatives. Solvent effects

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