Directionality of Double-Bond Photoisomerization Dynamics Induced by a Single Stereogenic Center.
In light-driven single-molecule rotary motors, the photoisomerization of a double bond converts light energy into the rotation of a moiety (the rotor) with respect to another (the stator). However, at the level of a molecular population, an effective rotary motion can only be achieved if a large majority of the rotors rotate in the same, specific direction. Here we present a quantitative investigation of the directionality (clockwise vs counterclockwise) induced by a single stereogenic center placed in allylic position with respect to the reactive double bond of a model of the biomimetic indanylidene-pyrrolinium framework. By computing ensembles of nonadiabatic trajectories at 300 K, we predict that the photoisomerization is >70% unidirectional for the Z → E and E → Z conversions. Most importantly, we show that such directionality, resulting from the asymmetry of the excited state force field, can still be observed in the presence of a small (ca. 2°) pretwist or helicity of the reactive double bond. This questions the validity of the conjecture that a significant double-bond pretwist (e.g., >10°) in the ground state equilibrium structure of synthetic or natural rotary motors would be required for unidirectional motion.
‡Institut de Chimie, Université de Strasbourg, CNRS UMR 7177, 1 rue Blaise Pascal, Strasbourg 67008, France.
Gabriel
G
Marchand
‡Institut de Chimie, Université de Strasbourg, CNRS UMR 7177, 1 rue Blaise Pascal, Strasbourg 67008, France.
Julien
J
Eng
Igor
I
Schapiro
§Department of Biotechnology, Chemistry and Pharmacy, University of Siena, via Aldo Moro, 2, Siena 53100, Italy.|⊥Unidad Docente de Química Física, Universidad de Alcalá, E-28871 Alcalá de Henares, Madrid, Spain.
Alessio
A
Valentini
⊥Unidad Docente de Química Física, Universidad de Alcalá, E-28871 Alcalá de Henares, Madrid, Spain.
Luis Manuel
LM
Frutos
§Department of Biotechnology, Chemistry and Pharmacy, University of Siena, via Aldo Moro, 2, Siena 53100, Italy.
Elisa
E
Pieri
§Department of Biotechnology, Chemistry and Pharmacy, University of Siena, via Aldo Moro, 2, Siena 53100, Italy.|∥Chemistry Department, Bowling Green State University, 141 Overman Hall, Bowling Green, Ohio 43403, United States.
Massimo
M
Olivucci
Jérémie
J
Léonard
‡Institut de Chimie, Université de Strasbourg, CNRS UMR 7177, 1 rue Blaise Pascal, Strasbourg 67008, France.
Etienne
E
Gindensperger
D007536:Isomerism; D008958:Models, Molecular; D013237:Stereoisomerism
ab initio nonadiabatic molecular dynamics; isomerization; molecular motor; photochemistry