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.