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Moncelsi, Giulia; Escobar, Luis; Dube, Henry; Ballester, Pablo (2018): 2-(4-Pyridyl-N-oxide)-Substituted Hemithioindigos as Photoresponsive Guests for a Super Aryl-Extended Calix[4]pyrrole Receptor. In: Chemistry-An Asian Journal, Vol. 13, No. 12: pp. 1632-1639
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We report the synthesis of two 2-(4-pyridyl-N-oxide)-substituted hemithioindigos (HTIs). We probed their photoisomerization by using UV/Vis and (HNMR)-H-1 spectroscopy techniques. Light irradiation at =450nm provoked the isomerization of the HTI Z isomer to the E counterpart to a large extent (approximate to 80% at the photostationary state). (HNMR)-H-1 titration experiments revealed the formation of thermodynamically and kinetically stable 1:1 inclusion complexes of the (Z)-HTI isomers with a super aryl-extended host (association constant>10(4)m(-1)). Photoirradiation at =450nm of the inclusion complexes induced the isomerization of the bound HTI N-oxide to afford the (E)-HTI< subset of>calix[4]pyrrole complex. We determined accurate association constant values for the 1:1 inclusion complexes of the (Z)- and (E)-HTI isomers by using isothermal titration calorimetry experiments. The results showed that the stability constants of the (E)-HTI complexes were 2.2-2.8-fold lower than those of the (Z)-HTI counterparts, which explains the lack of light-induced release of the former to the bulk solution.