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Updated: Jun 12, 2025

Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
Published on: September 18, 2016
Excited-state aromaticity reversals in norcorrole.
Peter B Karadakov1, Edward Cummings1
1Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK. peter.karadakov@york.ac.uk.
Aromaticity reversals occur in Ni(II) norcorrole and norcorrole upon electronic excitation. Antiaromatic ground states become aromatic in excited states, forming 24 π-electron systems.
Area of Science:
- Computational Chemistry
- Quantum Chemistry
- Organic Chemistry
Background:
- Norcorrole molecules, including Ni(II) norcorrole (NiNc) and norcorrole (H2Nc), exhibit antiaromatic characteristics in their ground electronic state (S0).
- Understanding the electronic behavior of these macrocycles upon excitation is crucial for their potential applications.
Purpose of the Study:
- To investigate aromaticity reversals between the ground (S0) and excited (T1 and S1) states of NiNc and H2Nc.
- To analyze the changes in aromaticity metrics and molecular geometry upon electronic excitation.
Main Methods:
- Calculated harmonic oscillator model of aromaticity (HOMA) values at optimized S0, T1, and S1 geometries.
- Analyzed nucleus-independent chemical shift (NICS) values and isotropic magnetic shielding distributions between S0 and T1 states.
Main Results:
- Aromaticity reversals were observed: antiaromatic S0 states transform into aromatic T1 and S1 states.
- Excited states exhibit Baird aromaticity with 24 π electrons.
- The geometries of the aromatic T1 and S1 states are more non-planar (larger bowl depths) than the antiaromatic S0 states.
Conclusions:
- NiNc and H2Nc undergo significant aromaticity changes upon electronic excitation.
- The study reveals a novel pathway to Baird aromaticity in these systems.
- The interplay between electronic state and molecular geometry influences aromaticity in norcorroles.
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