Topological Diversity in Electrochemically Active Core-Modified Expanded Porphyrinoids.

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Expanded porphyrinoids are macrocyclic compounds with tunable electronic and photophysical properties.
• Thiophene incorporation influences the conformational flexibility and electronic structure of these macrocycles.

Purpose of the Study:

• To investigate the conformational changes in thiophene-based expanded porphyrinoids with increasing numbers of thiophene units.
• To characterize the electronic properties and redox behavior of larger thiophene-based porphyrinoids.

Main Methods:

• Synthesis and characterization of thiophene-based expanded porphyrinoids.
• Variable temperature NMR spectroscopy to study conformational dynamics.
• Spectro-electrochemical measurements to probe redox properties.

Main Results:

• A transition from planar to twisted conformations was observed with increasing thiophene units.
• Octaphyrin (40π electrons) exhibited temperature-dependent conformational interconversion in solution, unlike its rigid solid-state structure.
• 60π-dodecaphyrin and 70π-tetradecaphyrin showed facile, reversible two-electron oxidation with unstable radical cation intermediates.

Conclusions:

• Conformational flexibility is a key feature of thiophene-based expanded porphyrinoids, influenced by π-electron count and conjugation.
• These systems offer potential for applications requiring dynamic molecular architectures and tunable redox properties.