Synthesis and Electrochemical Characterization of Acetylacetone (acac) and Ethyl Acetate (EA) Appended β-Trisubstituted Push-Pull Porphyrins: Formation of Electronically Communicating Porphyrin Dimers.

Two new families of "push-pull" tetraphenylporphyrins with one acetylacetone (acac) or ethyl acetate (EA) moiety at a β-pyrrole position of the macrocycle and two Br or Ph substituents at the antipodal β-positions were synthesized and structurally, spectroscopically, and electrochemically characterized. The examined porphyrins are represented as MTPP(R)acac and MTPP(R)EA (where R = Br or Ph and M = H, Co, Ni, Cu, or Zn). NiTPP(Br)acac exhibits an extremely nonplanar conformation (Δ24 = 0.44 Å, ΔC = 0.82 Å), while HTPP(Br)EA and ZnTPP(Ph)EA exhibit a quasi-planar conformation. All of the synthesized acac-appended porphyrins show a keto-enol tautomerism in solution, which results in formation of hydrogen bonded dimers as evidenced by H NMR and mass spectrometry. Dimers were also detected under the electrochemical conditions for the dibromo derivatives but not the diphenyl substituted porphyrins. A facile stepwise and reversible electrogeneration of the electronically communicating porphyrin dimers is observed for MTPP(Br)acac where M = Cu, Ni, or Zn.