Synthesis, Structural Characterization and Redox Properties of Porphyrinoids with Thiᴏphene and Thienothiᴏphenes

Abstract

Porphyrin and isophlorin are structural congeners of 18π and 20π annulenes are redox structural isomers through PCET. On the other hand, non-pyrrolic porphyrinoids usually tend to undergo reversible two-electron ring oxidation to yield aromatic dicationic species. Such studies are well documented in regular porphyrin-like structures. In this thesis, thiophene has been employed to construct porphyrinoids unconventional links between the heterocyclic units. A 8π COT thiophene fused annulene and its higher analogue 16π tetramer were synthesized in a one-pot reaction. 8π COT identified as non-planar and higher member displayed highly rigid planar conformation. In a comparative study, a core modified 24π expanded porphyrinoid and its higher homologues containing 48π decaphyrin and 72π pentadecaphyrin through McDonald type condensation were also synthesized. Apart from thiophene, furan and selenophene are also incorporated to the macrocyclic system to study their conformational dynamics and aromaticity. As non-pyrrolic porphyrinoids undergo one/two electron ring oxidation, they were identified by both chemical and electrochemical studies. Different thiophene/furan/selenophene containing hexaphyrins were synthesized by replacing the two thiophene units with the thienothiophene units. Spectroelectrochemistry studies confirmed the different oxidation states of these macrocycles. Finally, molecular structure was elucidated by the single crystal X-ray diffraction studies and their (anti)aromaticity supported through quantum chemical calculations.