Ground and Excited State Aromaticity in Azulene-Based Helicenes

Area of Science:

• Organic Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Helicenes are polycyclic aromatic hydrocarbons with a helical structure.
• Azulene is a non-alternant aromatic hydrocarbon isomer of naphthalene.
• Understanding electron delocalization is crucial for designing novel organic materials.

Purpose of the Study:

• To investigate electron delocalization in ground and excited states of azulene-containing helicenes.
• To explore the relationship between molecular size and aromaticity in these systems.
• To rationalize the observed electronic properties using advanced computational methods.

Main Methods:

• Synthesis of azulene-containing helicenes.
• Calculation of magnetically induced properties (IMS3D and ACID).
• Electron density decomposition analysis (EDDB) and wavefunction decomposition.

Main Results:

• Azulene-containing helicenes show ground-state charge separation absent in the triplet excited state.
• Helicenes with more than six fused cycles exhibit unexpected aromatic delocalization circuits.
• Wavefunction decomposition explains the emergence of these delocalization pathways.

Conclusions:

• Azulene incorporation into helicenes leads to unique electronic behaviors.
• Molecular size significantly influences aromaticity and electron delocalization in helicenes.
• The study provides insights into the fundamental electronic structure of complex polycyclic systems.