Open AccessStructural Modulation of Chromic Response: Effects of Binding‐Site Blocking in a Conjugated Calix[4]pyrrole Chromophore
Author(s) -
Březina Václav,
Ishihara Shinsuke,
Lang Jan,
Hanyková Lenka,
Ariga Katsuhiko,
Hill Jonathan P.,
Labuta Jan
Publication year - 2018
Publication title -
chemistryopen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 29
ISSN - 2191-1363
DOI - 10.1002/open.201800005
Subject(s) - chemistry , solvatochromism , chromophore , tetrapyrrole , protonation , titration , solvent , pyrrole , conjugated system , photochemistry , organic chemistry , inorganic chemistry , ion , polymer , enzyme
Herein, we modulate the chromic response of a highly colored tetrapyrrole macrocycle, namely, tetrakis(3,5‐di‐ tert ‐butyl‐4‐oxocyclohexadien‐2,5‐yl)porphyrinogen ( OxP ) by structural modification. N‐Benzylation at the macrocyclic nitrogen atoms leads to stepwise elimination of the two calix[4]pyrrole‐type binding sites of OxP and serial variation of the chromic properties of the products, double N‐benzylated Bz 2 OxP and tetra N‐benzylated Bz 4 OxP . The halochromic (response to acidity) and solvatochromic (response to solvent polarity) properties were studied by using UV/Vis spectroscopy and NMR spectroscopy in nonpolar organic solvents. Titration experiments were used to generate binding isotherms to elucidate their binding properties with difluoroacetic acid. Differences in the halochromic properties of the compounds allowed construction of a colorimetric scale of acidity in nonpolar solvents, as the compounds in the series OxP , Bz 2 OxP , and Bz 4 OxP are increasingly difficult to protonate but maintain their propensity to change color upon protonation. The concurrent effects of binding‐site blocking and modulation of acidity sensitivity are important new aspects for the development of colorimetric indicators.