Synthesis of 7,8-dehydropurpurin dimers and their conversion into conformationally constrained β-to-β vinylene-bridged porphyrin dimers

Norihito Fukui; Hideki Yorimitsu; Jong Min Lim; Dongho Kim; Atsuhiro Osuka

doi:10.1002/anie.201400632

Synthesis of 7,8-dehydropurpurin dimers and their conversion into conformationally constrained β-to-β vinylene-bridged porphyrin dimers

Angew Chem Int Ed Engl. 2014 Apr 22;53(17):4395-8. doi: 10.1002/anie.201400632. Epub 2014 Mar 18.

Authors

Norihito Fukui¹, Hideki Yorimitsu, Jong Min Lim, Dongho Kim, Atsuhiro Osuka

Affiliation

¹ Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan).

PMID: 24644098
DOI: 10.1002/anie.201400632

Abstract

7,8-Dehydropurpurin has attracted much attention owing to the dual 18π- and 20π-electron circuits in its macrocyclic conjugation. The two-fold Pd-catalyzed [3+2] annulation of meso-bromoporphyrin with 1,4-diphenylbutadiyne furnished 7,8-dehydropurpurin dimers. The 8(a) ,8(a) -linked dimer displays a red-shifted and enhanced absorption band in the NIR region and a small electrochemical HOMO-LUMO band gap as a consequence of efficient conjugation between the two coplanar 7,8-dehydropurpurin units. Treatment of this dimer with N-bromosuccinimide in chloroform and ethanol gave β-to-β vinylene-bridged porphyrin dimers. Owing to the highly constrained conformations, these dimers exhibit perturbed absorption spectra, small Stokes shifts, and high fluorescence quantum yields.

Keywords: 7,8-dehydropurpurin; conjugation; dimerization; porphyrinoids.