Cyclo[18]carbon: the smallest all-carbon electron acceptor

Area of Science:

• Computational Chemistry
• Materials Science
• Physical Chemistry

Background:

• Fullerene C60 is a well-known electron acceptor, but smaller all-carbon acceptors are sought for novel applications.
• Understanding the electronic and structural properties of novel carbon nanomaterials is crucial for their technological development.

Purpose of the Study:

• To computationally investigate the ground and excited state properties of the C18 molecule and its complexes with electron donors.
• To assess C18's potential as an electron acceptor and compare its properties to fullerene C60.
• To explore the impact of electron transfer on the Marcus regime in C18-donor complexes.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to study the electronic structure and excited states.
• High levels of exact exchange (Hartree-Fock, HF) in DFT functionals were used to accurately predict the polyynic structure of C18.
• Computational modeling of C18 in complexes with electron-donating molecules was performed.

Main Results:

• A high percentage of exact exchange in DFT functionals correctly predicted the polyynic structure of C18, aligning with experimental findings.
• In complexes with electron donors, C18 forms charge-separated excited states via electron transfer, establishing it as the smallest all-carbon electron acceptor.
• C18 exhibits a larger internal reorganization energy than C60, shifting electron transfer reactions to the normal Marcus regime under high driving forces.

Conclusions:

• C18 is a promising, small all-carbon electron acceptor with unique electronic properties.
• The computational approach accurately predicted C18's structure and its behavior in electron transfer processes.
• C18's distinct reorganization energy offers new possibilities for controlling electron transfer kinetics compared to C60.