Designing Force Probes Based on Reversible 6π-Electrocyclizations in Polyenes Using Quantum Chemical Calculations

Area of Science:

• Organic Chemistry
• Computational Chemistry
• Materials Science

Background:

• Conjugated π-systems in polyenes are susceptible to electrocyclic ring-closure reactions.
• These reactions can interrupt the π-system's conjugation.

Purpose of the Study:

• To investigate the reversibility of 6π-electrocyclization reactions in polyenes.
• To determine if external mechanical force can trigger the reverse (ring-opening) reaction.

Main Methods:

• Density functional calculations were employed to study model polyene systems.
• Systems were constrained in fused ring structures to promote ring-closure.
• External mechanical pulling forces were applied to the polyene chain termini.

Main Results:

• The forward 6π-electrocyclization reaction is exergonic with comparable reaction barriers.
• A pulling force of 2 nano-Newtons or less triggers the reverse reaction, making it exergonic.
• The ring-opening reaction proceeds with a low barrier under a 2 nano-Newton pulling force.
• Analysis revealed optimal C-C σ-bond activation upon ring opening with specific pulling positions.

Conclusions:

• External mechanical force is an efficient stimulus for triggering ring-opening reactions in polyenes.
• This force-induced reversibility offers a novel way to control conjugated π-systems.