Protonation Dependent Topological Dichotomy of Core Modified Hexaphyrins: Synthesis, Characterization, and Excited State Dynamics.

Two hitherto unknown core modified hexaphyrin analogues have been synthesized and characterized where the conformational dynamics of these macrocycles in the free base form is achieved by the rotation of thienothiophene units. Further unique property of these macrocycles is the Hückel-Möbius topological switching. The thermodynamic equilibrium and kinetics of the interconversion leading to Hückel-Möbius switches have been triggered by external stimuli, such as protonation and/or temperature. We have provided a thorough solution-state spectroscopic characterization, solid-state structural evidence combined with in-depth theoretical calculations to investigate the crucial factors involved in such interconversion between Hückel and Möbius topologies for these hexaphyrins which will be useful in designing future new members to expanded porphyrin chemistry.