Sigma- versus Pi-Dimerization Modes of Triangulene.

Area of Science:

• Computational Chemistry
• Materials Science
• Organic Chemistry

Background:

• Triangulene is a graphene nano-flake molecule with diradicaloid properties.
• Previous studies reported pancake-bonded pi-dimer isomers of triangulene.

Purpose of the Study:

• To investigate the aggregation and dimerization modes of triangulene.
• To explore the stability and electronic properties of different triangulene dimer configurations.
• To elucidate the reasons behind the experimental observation of only pi-dimers for trioxo-triangulene derivatives.

Main Methods:

• Density Functional Theory (DFT) modeling was employed to investigate triangulene dimerization.
• Calculations explored various dimerization modes, including sigma-bonded and pi-bonded isomers.
• Analysis of interaction energies and electronic states (singlet, triplet, quintet) was performed.

Main Results:

• Six new doubly bonded sigma-dimers of triangulene were identified, in addition to known pi-dimers.
• The identified sigma-dimers exhibit a range of stabilities, with the most stable having an interaction energy of -25.17 kcal/mol.
• An open-shell, singly sigma-bonded diradicaloid dimer was also discovered.
• An isomerization pathway between different dimer types and their electronic states was elucidated.
• The study provides reasons for the exclusive experimental observation of pi-dimers in trioxo-triangulenes.

Conclusions:

• Triangulene exhibits diverse dimerization capabilities beyond previously known pi-dimers.
• The electronic and stability properties of sigma-dimers differ significantly, including diradicaloid species.
• Understanding these dimerization pathways and electronic states is crucial for explaining experimental observations in related molecules like trioxo-triangulenes.