Theoretical Study of the Isomerization Mechanism of Azobenzene and Disubstituted Azobenzene Derivatives

Abstract

A series of azobenzenes was studied using ab initio methods to determine the substituent effects on the isomerization pathways. Energy barriers were determined from three-dimensional potential energy surfaces of the ground and electronically excited states. In the ground state (S(0)), the inversion pathway was found to be preferred. Our results show that electron donating substituents increase the isomerization barrier along the inversion pathway, whereas electron withdrawing substituents decrease it. The inversion pathway of the first excited state (S(1)) showed trans --> cis barriers with no curve crossing between S(0) and S(1). In contrast, a conical intersection was found between the ground and first excited states along the rotation pathway for each of the azobenzenes studied. No barriers were found in this pathway, and we therefore postulate that after n --> pi (S(1) <-- S(0)) excitation, the rotation mechanism dominates. Upon pi --> pi (S(2) <-- S(0)) excitation, there may be sufficient energy to open an additional pathway (concerted-inversion) as proposed by Diau. Our potential energy surface explains the experimentally observed difference in trans-to-cis quantum yields between S(1) and S(2) excitations. The concerted inversion channel is not available to the remaining azobenzenes, and so they must employ the rotation pathway for both n --> pi and pi --> pi excitations.

Optical properties of azobenzene-functionalized self-assembled monolayers: Intermolecular coupling and many-body interactions

“…These findings are in agreement with previous studies on trans-azobenzene in the gas phase. [51][52][53] In particular, the highest occupied molecular orbital, HOMO (H), is distributed almost exclusively on the N− −N bond, thus being a non-bonding (n) orbital. On the other hand, the H-1 and the lowest unoccupied molecular orbital, LUMO (L) exhibit π character with the electron density spread over the phenyl rings.…”

The Kinetics of the Cis-to-Trans Thermal Isomerization of 4-Anilino-4’- Nitroazobenzene are Highly Influenced by Solvent Polarity

“…Azobenzenes are common organic dyes that have been extensively studied both experimentally and theoretically owing to their potential applications in material science, medicinal chemistry, molecular switches and other devices [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. They are photo-reactive molecules that undergo reversible photo-isomerization from the more stable trans-isomer to the less stable cis-isomer.…”

Electron photodetachment dissociation of DNA anions with covalently or noncovalently bound chromophores

“…In a photostable quencher, all electronic energy is converted into vibrational energy. In the case of azobenzenes like DABSYL, the relaxation to the electronic ground state involves trans-cis isomerization of the NϭN bond [16]. Azobenzene chromophores can therefore be used to locally deposit vibrational internal Scheme 1 energy and probe its redistribution over the biomolecule [17].…”