Issue 33, 2018

Conjugated double helices via self-dimerization of α,α′-dianilinotripyrrins

Abstract

A new motif for artificial double helices was developed on the basis of α,α′-disubstituted tripyrrin. α,α′-Dibromotripyrrin 3 was prepared by gentle bromination at the pyrrolic α-positions of 5,10-diphenyltripyrrane followed by oxidation with DDQ. Nucleophilic substitution reactions of 3 with anilines proceeded efficiently to furnish a series of α,α′-dianilinotripyrrins 4–11, which displayed monomeric and dimeric forms depending upon the solvent used for crystallization and the structures of the substituted anilines. Dimeric forms show double helical structures with smooth π-conjugation as indicated by their absorption spectra. van't-Hoff plot analyses revealed that the dimerizations in CDCl3 are enthalpy-driven. Larger association constants of the dimerization are attained for 3,5-di-t-butylanilino- and 3,5-bis(trifluoromethyl)anilino-substituted tripyrrins (7 and 8) via additional multiple intermolecular interactions. In a nonpolar and aprotic solvent, tripyrrins (9 and 10) bearing bulkier 1-naphthylamino and mesitylamino groups do not dimerize but undergo unique tautomerization.

Graphical abstract: Conjugated double helices via self-dimerization of α,α′-dianilinotripyrrins

Supplementary files

Article information

Article type
Edge Article
Submitted
22 Jun 2018
Accepted
16 Jul 2018
First published
17 Jul 2018
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2018,9, 6853-6859

Conjugated double helices via self-dimerization of α,α′-dianilinotripyrrins

M. Umetani, T. Tanaka and A. Osuka, Chem. Sci., 2018, 9, 6853 DOI: 10.1039/C8SC02739K

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