Correlation between Absorption and Substitution of Photochromic 1,2‐Bis(thienyl)ethenes (BTEs) Using Modified Spectroscopic Hammett Equations

Abstract

Series of photochromic 1,2-bis(thienyl)ethenes possessing perfluorocyclopentene backbones, either hydrogen or methyl groups at the β-positions of the thiophenes, and a variety of substituents in their α'-positions were prepared, which cover the range from electron-donating to electron-withdrawing (Me, À CH 2 OH, À OTBS, À TMS, À Br, 1,3-dioxan-2-yl, pyridin-4-yl, À CH 2 OH, À COOH). As a linear free energy relationship the spectroscopic Hammett equation gives fair to excellent fits to the excitation energy of the absorption maxima of the ring-opened as well as the ring-closed forms of the BTEs, when Hammett substituent constants σ p were replaced by Brown's modified substituent constants σ p + and σ p À . Vice versa, hitherto unknown Hammett-Brown substituent constants can be estimated from the UV spectra. Furthermore, we compared the experimentally measured absorption maxima with values which we calculated by three different methods (DFT STEOM-DLPNO-CCSD/def2-TZVPP, TD-DFT ωB97X-D3/6-31G*, TD-DFT ωB97X-D3/6-311 + + G**).

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

“…The value of the 1,3-dioxane-2-yl group was determined by us by application of the spectroscopic Hammett–Brown equation, as there is no constant available from the literature for this substituent. 27 As it can be seen from the UV/vis-spectra, the electron-withdrawing groups, e.g . –CHO, lead to a bathochromic shift and the electron-donating groups lead to a hypsochromic shift.…”

“…To understand the effect of the methoxymethyl groups we compared the spectrocopic data with those of the reference compound shown in Scheme 4 , which was prepared as described earlier. 27 Table 5 shows the quantum yields and the molar absorption coefficients. Comparing 15a and the reference BTE reveals that the MOM group increases the molar absorption coefficient ε A of the ring-opened form, whereas the quantum yields φ A,B decrease slightly.…”

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

“…The compounds 12a , 12e , 13a , 16a , 18 , 19a , 19c and 20 are described in our previous paper. 9,10…”

“…The compounds 12a,12e,13a,16a,18,19a,19c and 20 are described in our previous paper. 9,10 General procedure of the Suzuki-Miyaura coupling (procedure 1)…”

“…Recently, we reported on linear free enthalpy relationships on applying the spectroscopic Hammett–Brown equation to correlate substituent effects and absorption maxima of BTEs. 9 In addition, we described BTEs which are part of prolonged push–pull-chromophors to induce bathochromic absorption maxima, 10 and BTEs with α/α′-MOM groups. 11 According to the literature several aspects should be considered on designing fatigue resistant BTEs for technical applications.…”