Study of scrambling in porphyrin forming reactions: Synthesis, structure, photophysical, electrochemical and antimicrobial studies

Three classes of scrambled porphyrins (Class 1-3) were synthesized by MacDonald type 2 + 2 condensation reactions of electron deficient dipyrromethanes with aldehyde and its complementary reactions in presence of mild acid catalysts. Overall, BF3.OEt2 catalyzed reactions yield more scrambled products than TFA catalyzed. All the scrambled porphyrins were characterized by the conventional spectroscopic methods. A marginal red shift (2-3 nm) was observed in Soret band upon installation of two or three 4-cyanophenyl/4-carboxymethylphenyl groups at the meso-position of porphyrin 1 with the subsequent removal of pentafluorophenyl groups. The first emission exhibits a bathochromic shift of 4-5 nm when a pentafluorophenyl ring detached from 1 with the subsequent addition of 4-cyanophenyl group; first emission intensity is less compared to the second one which increases as it moves from 2 to 5. The copper complex, Cu-8 has been structurally characterized by single crystal X-ray diffraction analysis and the role of weak intermolecular interactions in their crystal packing has been analyzed and quantified using Hirshfeld surface analysis. Electrochemical studies revealed that a gradual increase of positive shift in the first reduction/oxidation potentials of Class 1 and 2 porphyrins upon installation of pentafluorophenyl ring with subsequent removal of 4-cyanophenyl/4-carboxymethylphenyl ring on either H2T(4-CNP)P or H2T(4-CMP)P; the HOMO-LUMO energy gap is found to be decreased in Class 1 porphyrins whereas it is increased in Class 2 porphyrins. The highest antimicrobial activity is observed for porphyrin 5. (C) 2017 Elsevier Ltd. All rights reserved.