Ab Initio Molecular Orbital and Density Functional Studies on the Stable Structures and Vibrational Properties of trans- and cis-Azobenzenes

Abstract

The structure of trans-azobenzene (TAB) has been a subject of controversy in experimental and theoretical studies. To provide the theoretical basis for stable structures and vibrational properties of TAB and cisazobenzene (CAB), we performed ab initio molecular orbital calculations based on the second-order Møller-Plesset (MP2) method and density functional theory (DFT). Only the MP2 calculation accounting for the diffuse basis set (6-31+G*) leads to the distorted structure of TAB, which is consistent with the gas-phase electron diffraction experiment. The Hartree-Fock and DFT (PW91PW91, MPW91, BP86, and B3LYP) calculations, on the other hand, result in the almost planar structure of TAB. The frequencies of normal modes of TAB and CAB are calculated most accurately by the PW91PW91/6-31+G* method followed by the BP86/6-31G* method. These results are expected to provide useful benchmark data on the accuracy of MP2 and DFT methods for describing the structural and vibrational properties of azobenzene-like molecules, which consist of weakly interacting phenyl rings.

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

“…47 The similar reaction mechanism was also reported in the dynamics simulations by Doltsinis et al 45,49,50 and Thiel et al 55 As described above, the transient Raman spectra indicate that the NN stretching frequency of trans-azobenzene is almost unchanged (decreases by only 12 cm −1 ) in the S 1 (nπ * ) state. 12 There are several theoretical reports on vibrational frequencies for trans-azobenzene in the ground state at the MP2, density functional theory (DFT), and CASSCF levels, 20,21,23,25,30 while, to our knowledge, there is only one report on frequencies of trans-azobenzene in the S 1 (nπ * ) state, which employed the CASSCF method. 30 However, the CASSCF method is sometimes insufficient for the quantitative discussion of geometries and frequencies because dynamical correlation effects are not taken into account.…”

Vibrational analysis of [4-[(E)-phenylazo] phenyl]ethanol based on the comparison between the experimental and DFT calculated Raman spectra

“…From a numerical point of view, the Raman intensities, as a function of the third derivatives of the energies, are both dependant on the energetic models (basis set truncation, treatment of electron correlation), the methods and the parameters used to calculate the analytical and numerical derivatives [60]. Regarding azobenzene derivatives, different theoretical studies were performed with the aim of improving the assignment and the description of the normal modes [43][44][45][46][47][48][49][50][51]. Different methods were tested and although some important information was extracted, the questions concerning the chemistry models still remain open.…”

“…Consequently, under illumination, each type of azobenzene derivatives has its own steady state composition and the different configurations as well as the knowledge of the conversion mechanism are crucial for the identification and quantification. For these reasons, various spectroscopic techniques have been extensively used, including UV-Vis optical absorption experiments [41,43] and vibrational spectroscopy [39]. The N=N stretching vibration, characteristic of the azobenzene group, can be involved in several vibrational bands, which makes the assignment of the Raman spectra more difficult.…”

“…The N=N stretching vibration, characteristic of the azobenzene group, can be involved in several vibrational bands, which makes the assignment of the Raman spectra more difficult. Consequently, from the middle of the 90's, theoretical studies were performed to improve the assignment and description of the normal modes in azobenzene and their derivatives [43][44][45][46][47][48][49][50][51]. In this study, we assessed the capacity of the B3LYP/6-311++G(2d,2p) method to reproduce the .…”

Photoinduced Change of UV‐Absorption and Redox Potential of Alkyne‐Bridged Diferrocenyl Azobenzene Derivative

“…In order to understand the change of absorbency and oxidation potential, the geometry of trans-DFAA was optimized by three parameterized Becke-LeeYang-Parr (B3LYP) hybrid exchange-correlation function [17]. In transoptimized structure (see Figure 3(b)), the azo and phenyl groups are located nearly on a plane in optimized molecular structure, the dihedral angle of Ph-N=N-Ph was near to 0…”