β-Tetraethyl-β‘-tetrapyridin-4-yl Porphyrins, Their N-Methylated Tetracations, and Heterodimers with ms-Tetraphenylsulfonato Porphyrins

A mixture of the four regioisomers of β-tetraethyl-β‘-tetrapyridin-4-yl porphyrins and their N-methylated tetracations has been synthesized. The crystal structure of regioisomer I is determined by complicated edge-on interactions between the pyridinyl substituents, which arrange as a “bowl”. The nonseparable mixture of regioisomers III+IV is extremely well soluble in chloroform and, as tetramethylated tetracation, in water (≅10 -1 M). It forms well-defined and water-soluble (5 × 10 -4 M) heterodimers with ms-tetraphenylsulfonatoporphyrin as a free base, a zinc and a copper complex ( K dimer = 1.3 × 10 8 M -1 ). Dimers containing one copper porphyrinate show no fluorescence. Cofacial porphyrin−porphyrin distances were estimated from transition dipole interaction as 7−8 Å. Tetracationic zinc porphyrinates are stable against acid demetalation, the corresponding free base is not protonated down to pH 1. NH-Deprotonation has been achieved with sodium hydroxide and leads to chain-like assemblies in water. Application of the new porphyrins in vesicle entrapment measurements, formation of electron donor−acceptor pairs, and molecular assemblies is shortly discussed.