Stabilities of bis(thienyl)ethenes in polymethyl methacrylate (PMMA) coatings as absorbance modulation layers for nanoscale imaging

For absorption modulation layers for nanoscale imaging, a series of photochromic 1,2-bis(thienyl)ethenes (BTEs) was prepared, spectroscopically characterized in solution, and fatigue resistancies in PMMA films were investigated. The BTEs examined possess hydrogen or methyl groups in the beta-position (C4/C4 ') of the thiophene wings. The non-symmetrically substituted BTEs studied are substituted at the C5/C5 '-positions of the thiophenes with combinations of pyridin-3-yl, pyridin-4-yl, 3-PhOMe, 4-PhOMe, 3-PhOH, and 4-PhOH groups. The substitution pattern of the symmetric BTEs studied was varied over a broad range (Ph, 4-tol, 4-PhOMe, 4-PhOH, pyridin-4-yl, 5-Me-thiophen-2-yl, 6-MeO-naphthalen-2-yl). In addition, a benzothiophene derivative was examined. It was shown that the stabilities in PMMA films cannot be derived from results in solution. Thus, the beta-methylated BTEs proved to be less stable in PMMA films than their non-methylated counterparts. Best fatigue resistancies were obtained when a BTE with cross-conjugated 3,3-connectivity of a pyridin-3-yl at C5 and a 3-methoxyphenyl group at C5 ' without methyl groups at C4/C4 ' was applied. Substitution by 4-anisyl groups at C5/C5 ' gave the best fatigue resistancies of the series of symmetrically substituted BTEs. The benzothiophene derivative proved to be less stable in PMMA films than its thiophene analog. Stabilities of substituted BTEs in PMMA films are described which differ from those in solution.