Control of 1,3-Cyclohexadiene Photoisomerization Using Light-Induced Conical Intersections

TL;DR

This study demonstrates how ultrafast laser pulses can control the photoisomerization of 1,3-cyclohexadiene by inducing light-controlled conical intersections, offering a new way to manipulate molecular reactions with light.

Contribution

It introduces the concept of light-induced conical intersections and shows how laser polarization and timing can suppress specific isomerization pathways.

Findings

Laser field suppresses isomerization when polarized parallel to excitation dipole.

Timing of laser pulse is critical for effective control.

Theoretical model explains the mechanism via resonant coupling at conical intersections.

Abstract

We have studied the photo-induced isomerization from 1,3-cyclohexadiene to 1,3,5-hexatriene in the presence of an intense ultrafast laser pulse. We find that the laser field maximally suppresses isomerization if it is both polarized parallel to the excitation dipole and present 50 fs after the initial photoabsorption, at the time when the system is expected to be in the vicinity of a conical intersection that mediates this structural transition. A modified ab initio multiple spawning (AIMS) method shows that the laser induces a resonant coupling between the excited state and the ground state, i.e., a light-induced conical intersection. The theory accounts for the timing and direction of the effect.