title: Synthesis of 7,8-dehydropurpurin dimers and their conversion into conformationally constrained β-to-β vinylene-bridged porphyrin dimers.
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.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan).
authors.forename: Norihito
authors.initials: N
authors.lastname: Fukui
authors.forename: Hideki
authors.initials: H
authors.lastname: Yorimitsu
authors.forename: Jong Min
authors.initials: JM
authors.lastname: Lim
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
authors.forename: Atsuhiro
authors.initials: A
authors.lastname: Osuka
keywords: 7,8-dehydropurpurin; conjugation; dimerization; porphyrinoids