Bis(thienyl)ethenes with a-methoxymethyl groups. Syntheses, spectroscopic Hammett plots, and stabilities in PMMA films

A series of bis(thienyl)ethenes (BTEs) possessing perfluorocyclopentene backbones and methoxymethyl groups (MOM) in the 2/2 & PRIME;-positions of the thiophenes was prepared and examined. The substitution pattern of the 5/5 & PRIME;-positions was varied, covering the range from electron-donating to electron-withdrawing. The substituent effects of the absorption wavelengths of the ring-opened and the ring-closed isomers, which are interconverted by reversible 6 & pi;-electrocyclizations and cycloreversions, are studied by means of the spectroscopic Hammett equation and the Hammett-Brown equation. Excellent correlations of these linear free energy relationships were found, when the & sigma;p values of the Hammett equation, which summarize inductive, mesomeric and field effects, were replaced to the Hammett-Brown & sigma;p+ and & sigma;p- values which also take direct conjugation into account. We studied solvent effects on the spectroscopic properties and embedded the BTEs into polymethylmethacrylate (PMMA) coatings to examine their fatigue resistance. By our studies, the spectroscopic properties of BTEs can be adjusted by variation of the substitution pattern to a desired excitation wavelength for switching processes. MOM-substituted BTEs are described, applied to the spectroscopic Hammett equation and examined with respect to their photoresistency.

Automated summary

We synthesized and studied a series of bis(thienyl)ethenes (BTEs) with perfluorocyclopentene backbones and methoxymethyl groups at the 2/2' positions of the thiophenes. The substitution pattern at the 5/5' positions was varied from electron-donating to electron-withdrawing. By studying the effects of the substituents on the absorption wavelengths of the ring-opened and ring-closed isomers, we found excellent correlations using the spectroscopic Hammett equation and the Hammett-Brown equation, which took direct conjugation into account. We also investigated the solvent effects on the spectroscopic properties and tested the fatigue resistance of the BTEs embedded in PMMA coatings.