Controlling the Diradical Character of Thiele Like Compounds

Area of Science:

• Organic Chemistry
• Theoretical Chemistry
• Materials Science

Background:

• Organic diradicals are crucial in chemistry, biochemistry, and materials science.
• The singlet-triplet energy gap defines the diradical character of these molecules.

Purpose of the Study:

• Investigate how chemical substituents affect the singlet-triplet energy gap in p-quinodimethane (pQDM) and Thiele's hydrocarbons.
• Understand the role of substituents in controlling diradical character.

Main Methods:

• High-level theoretical calculations were employed.
• Analysis of substituent effects on singlet-triplet energy gap.
• Electronic spectra were calculated.

Main Results:

• Substituent nature critically controls the singlet-triplet energy gap, influencing ground-state diradical character.
• Steric effects are dominant for pQDM analogues; central ring substituents have minor impact.
• For Thiele's compounds, electron-withdrawing groups favor a non-diradical form, while electron-donating groups favor diradical forms up to 6-π electrons.

Conclusions:

• Chemical substituents offer a powerful tool for tuning the diradical nature of pQDM and Thiele's hydrocarbons.
• Understanding these effects allows for the design of novel organic materials with specific diradical properties.
• Predicted electronic spectra suggest potential applications in visible and near-IR regions.