First‐Principles Simulation of the Photoreaction of a Capped Azobenzene: The Rotational Pathway is Feasible

Photoisomerization of a bridged azobenzene derivative (AB-C(2)) is studied by nonadiabatic ab initio molecular dynamics simulation. The effect of the alkyl bridge linking the two phenyl rings on the Z → E and E → Z photoisomerization pathways and efficiencies is analyzed by detailed comparison to the unbridged parent compound. It is found that the bridge makes E → Z photoisomerization considerably faster and increases its quantum yield, whereas Z → E photoswitching is slightly hindered and has a significantly lower quantum yield although still being ultrafast. The simulations reveal that unsuccessful Z → E photoisomerization attempts can interconvert two pro-enantiomeric forms of Z-AB-C(2) via pseudorotation in the excited electronic state.

Section: Introductionsupporting

confidence: 91%

Enhanced photoswitching of bridged azobenzene studied by nonadiabatic ab initio simulation

Böckmann

Doltsinis

Marx

2012

“…27,28,30,31,42,58 On-the-fly dynamics simulations were also performed for the photoisomerization of azobenzene on the basis of semiempirical molecular orbital calculations with the surface hopping method 29,33,55,59,61 and with the multiple spawning method. 32 Recently, ab initio molecular dynamics (AIMD) simulations at the CASSCF level 26,47,54,57 and Car-Parrinello molecular dynamics simulations 34,45,49,50 were also performed for the photoisomerization of azobenzene in nπ * excitation. In our surface hopping AIMD simulation 47 at the state-averaged CASSCF (SA-CASSCF) level, it was shown that cis to trans isomerization in nπ * excitation occurs via two-step rotation mechanism, accompanying rotations of the central NN part and two phenyl rings, and this process can be classified into two types with respect to the orientation of the rotation, namely, clockwise and counterclockwise rotation pathways; the calculated quantum yields and lifetime in the excited states are in very good agreement with the corresponding experimental results.…”

Section: Introductionmentioning

confidence: 99%

A multireference perturbation study of the NN stretching frequency of trans-azobenzene in nπ* excitation and an implication for the photoisomerization mechanism

Harabuchi

Ishii

Nakayama

et al. 2013

A multireference second-order perturbation theory is applied to calculate equilibrium structures and vibrational frequencies of trans-azobenzene in the ground and nπ * excited states, as well as the reaction pathways for rotation and inversion mechanism in the nπ * excited state. It is found that the NN stretching frequency exhibits a slight increase at the minimum energy structure in the nπ * state, which is explained by the mixing of the NN stretching mode with the CN symmetric stretching mode. We also calculate the NN stretching frequency at several selected structures along the rotation and inversion pathways in the nπ * state, and show that the frequency decreases gradually along the rotation pathway while it increases by ca. 300 cm −1 along the inversion pathway. The frequencies and energy variations along the respective pathways indicate that the rotation pathway is more consistent with the experimental observation of the NN stretching frequency in nπ * excitation.

“…With restricted open-shell KohnSham ͑ROKS͒ theory 6,7 this approach has been extended to the simulation of photoreactions. [8][9][10][11] In this field on-the-fly simulations are particularly useful because the motion of the nuclei can be modeled for all degrees of freedom. The dynamics of the relaxation from the Franck-Condon regioncorresponding to an excited state system with approximately ground state geometry-to the minimum of the excited state can be simulated.…”

Section: Introductionmentioning

confidence: 99%

Restricted open-shell Kohn-Sham theory: Simulation of the pyrrole photodissociation

Frank

Damianos

2007

Self Cite

The authors study the photodissociation reactions of pyrrole and N-methylpyrrole using first-principles molecular dynamics. The first excited state is described with restricted open-shell Kohn-Sham theory. They find a small barrier in the excited state potential energy surface. The possibility of energy redistribution near the Franck-Condon region leads to two different reaction channels in on-the-fly simulations on a single diabatic potential energy surface. The results are discussed in comparison with previous ab initio calculations and with experiments.