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2‐(4′‐Pyridyl‐ N ‐oxide)‐Substituted Hemithioindigos as Photoresponsive Guests for a Super Aryl‐Extended Calix[4]pyrrole Receptor
Author(s) -
Moncelsi Giulia,
Escobar Luis,
Dube Henry,
Ballester Pablo
Publication year - 2018
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201800463
Subject(s) - photoisomerization , isomerization , photostationary state , chemistry , isothermal titration calorimetry , aryl , titration , pyrrole , oxide , photochromism , binding constant , inclusion compound , crystallography , photochemistry , stereochemistry , molecule , organic chemistry , catalysis , binding site , alkyl , biochemistry
We report the synthesis of two 2‐(4′‐pyridyl‐ N ‐oxide)‐substituted hemithioindigos (HTIs). We probed their photoisomerization by using UV/Vis and 1 H NMR spectroscopy techniques. Light irradiation at λ =450 nm provoked the isomerization of the HTI Z isomer to the E counterpart to a large extent (≈80 % at the photostationary state). 1 H NMR 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 λ =450 nm of the inclusion complexes induced the isomerization of the bound HTI N ‐oxide to afford the ( E )‐HTI⊂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.