Related Experiment Video
Updated: Jun 10, 2026

Light-driven Molecular Motors on Surfaces for Single Molecular Imaging
Published on: March 13, 2019
On the light-driven isomerization of a model asymmetric molecular rotor: conformations and conical intersections of
Mariana Assmann1, Guillermo Pérez-Hernández, Leticia González
1Institut für Physikalische Chemie, Friedrich-Schiller-Universität Jena, Helmholtzweg 4, 07743 Jena, Germany.
Abstract:
The ground state potential energy surface of the model molecular rotor 2-cyclopentylidene-tetrahydrofuran (CPTHF) has been characterized by calculating minimum energy conformations, racemization pathways, and rotational barriers with high level ab initio electronic structure calculations. Two conformers with their corresponding enantiomers are found. The activation barriers for racemization are negligible, therefore thermal racemization takes place at room temperature. Torsional transition states, calculated using multiconfigurational CASSCF calculations, show twisted and pyramidalized biradical structures. Additionally, the photochemistry of CPTHF has been investigated using the accurate MS-CASPT2/CASSCF methodology. In the UV spectrum it is found that the spectroscopic state is the S(1), which corresponds to a pipi* transition within the ethylene moiety. To understand light-triggered isomerization around the C=C bond, five conical intersections between the S(0) and S(1) have been located for each conformer of CPTHF, which allow the system to rapidly decay to the electronic ground state.
Related Concept Videos
Stereoisomerism of Cyclic Compounds
Chair Conformation of Cyclohexane
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this staggered...
Thermal Electrocyclic Reactions: Stereochemistry
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Photochemical Electrocyclic Reactions: Stereochemistry
Selection Rules: Photochemical Activation
Woodward–Hoffmann Selection Rules and Microscopic Reversibility
Thermal and Photochemical Electrocyclic Reactions: Overview

