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β‑Functionalized Dibenzoporphyrins with Mixed Substituents Pattern: Facile Synthesis, Structural, Spectral, and Electrochemical Redox Properties

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journal contribution
posted on 01.02.2019, 13:33 by Nitika Grover, Nivedita Chaudhri, Muniappan Sankar
A new series of mixed β-substituted dibenzoporphyrins were synthesized, and the effect of β-substitution on the spectral and electrochemical redox properties of the macrocycle was elucidated. The synthetic route to β-tetrasubstituted dibenzoporphyrins begins with the regioselective bromination of NiTPP­(Benzo)2 to afford NiTPP­(Benzo)2­Br4, followed by Pd catalyzed coupling reaction to access NiTPP­(Benzo)2­(R)4 (R = phenyl (Ph) and phenylethynyl (PE)). Synthesized benzoporphyrins exhibited red-shifted absorption spectral features with tunable redox properties. These benzoporphyrins displayed pronounced electronic effects of β-substituents on the macrocyclic skeleton. NiTPP­(Benzo)2­(PE)4 exhibited the lowest HOMO–LUMO gap among the series due to extended π-conjugation. Intrestingly, metal-centered oxidation of Ni­(II)/​Ni­(III) was observed for NiOPP­(Benzo)2 and NiOPP­(Benzo)­Br2 after an initial conversion of the neutral porphyrin to its dicationic form under electrochemical conditions.