Synthesis of 7,8-Dehydropurpurin Dimers and Their Conversion into Conformationally Constrained P-to-p Vinylene-Bridged Porphyrin Dimers

摘要

7,8-Dehydropurpurin has attracted much attention owing to the dual 18k-and 20n-electron circuits in its macrocyclic conjugation. The two-fold Pd-catalyzed [3+2J annulation of meso-bromoporphyrin with 1,4-diphenylbuta-diyne 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.