Azo-group dihedral angle torsion dependence on temperature: A theorerical–experimental study

Boni, Leonardo De; Toro, Carlos; Zílio, Sérgio Carlos; Mendonça, Cleber Renato; Hernández, Florencio E.

doi:10.1016/j.cplett.2010.01.039

Cited by 16 publications

(13 citation statements)

References 33 publications

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“…It has been previously suggested that the variation of the phenyl dihedral angles is responsible for slight changes observed in the UV absorption spectrum of azobenzene in the 20-120 1C temperature range. 107 Here, we shall demonstrate that the phenyl ring torsions are also responsible for distinctive peculiarities observed in the vibrational spectra of the compound, even at cryogenic temperatures. The largest deviations of the AB molecule from the equilibrium geometry, related to the tNNCC coordinates, correspond to the displacements along the C i diagonal in E-AB, and along the C 2 diagonal in Z-AB.…”

Section: Geometries Of E-ab and Z-abmentioning

confidence: 73%

Structural and spectroscopic characterization of E- and Z-isomers of azobenzene

Duarte

Fausto

Reva

2014

Phys. Chem. Chem. Phys.

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Monomers of azobenzene were isolated in argon matrices at 15 K and characterized by infrared spectroscopy and theoretical calculations. When the equilibrium vapors existing over the azobenzene crystals at room temperature were trapped in the matrix, only the thermodynamically most stable E-azobenzene was detected. In an attempt to convert E-azobenzene into the Z isomer, the matrix-isolated E-monomers were irradiated either by broad-band or narrow-band UV-visible light of different wavelengths, in the 600-200 nm range. However, no E-to-Z transformation was observed under these conditions. In an alternative experiment, E-azobenzene was irradiated by UV-visible broad-band light in the gas phase prior to trapping in a matrix. In this case, the E-to-Z photoisomerization occurred, and both E- and Z-azobenzene monomers were detected in the matrix sample. Subsequent irradiation of the matrix with narrow-band tunable visible or UV light (λ < 550 nm) resulted in back conversion of Z-azobenzene into the E-form. The observed photoinduced E-to-Z isomerizations allowed for the reliable vibrational characterization of both azobenzene isomers. The two-dimensional potential energy surfaces of Z- and E-azobenzene were explored as functions of the torsional movement of the two phenyl rings. They exhibit large flat areas around the minima, for both isomers, allowing for large-amplitude zero-point torsional vibrations. For the Z-form, these vibrations were found to be responsible for significant changes in the equilibrium NN bond length (up to 0.3 pm). This also allowed to explain the experimentally observed frequency smearing of the N=N stretching vibration in this isomer.

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Section: Geometries Of E-ab and Z-abmentioning

confidence: 73%

Structural and spectroscopic characterization of E- and Z-isomers of azobenzene

Duarte

Fausto

Reva

2014

Phys. Chem. Chem. Phys.

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“…Electronic properties of azobenzene were studied many times both experimentally and theoretically. ,,,− The first absorption band at 443 nm is attributed to the nπ* transition, whereas the second absorption band at 317 nm to the ππ* transition. Photochemical isomerization takes place on a femtosecond to picosecond timescale. , UV–vis absorption spectra of azobenzene isomers were measured or calculated in various solvents as well as in the gas phase. ,,,− The temperature dependence of the ( E )-azobenzene UV–vis absorption spectra was previously described by De Boni et al and by some of us . In the present study, we combined experimental and theoretical approaches to address in detail features observed for the thermal difference of the ( E )-azobenzene UV–vis absorption spectra.…”

Section: Introductionmentioning

confidence: 88%

“…Azobenzene is also frequently used as an actinometer . Because of its importance, azobenzene belongs among the best-studied molecular systems both experimentally and theoretically. − It might, therefore, come as a surprise that even the absorption spectra of both isomers of azobenzenea very basic photophysical characteristicsuffered from relatively large experimental errors until recently . The problem stemmed from the enormous photosensitivity of azobenzene.…”

Section: Introductionmentioning

confidence: 99%

“…24,25 UV−vis absorption spectra of azobenzene isomers were measured or calculated in various solvents as well as in the gas phase. 25,29,30,34−38 The temperature dependence of the (E)-azobenzene UV−vis absorption spectra was previously described by De Boni et al 22 and by some of us. 29 In the present study, we combined experimental and theoretical approaches to address in detail features observed for the thermal difference of the (E)azobenzene UV−vis absorption spectra.…”

Section: Introductionmentioning

confidence: 99%

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Limits of the Nuclear Ensemble Method for Electronic Spectra Simulations: Temperature Dependence of the (E)-Azobenzene Spectrum

Sršeň

Sita

Slavı́ček

et al. 2020

J. Chem. Theory Comput.

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We explore the range of applicability of the nuclear ensemble method (NEM) for quantitative simulations of absorption spectra and their temperature variations. We formulate a "good practice" for the NEM based on statistical theory. Special attention is paid to proper treatment of uncertainty estimation including the convergence with the number of samples, which is often neglected in the field. As a testbed, we have selected a well-known chromophore, (E)-azobenzene. We measured its temperature difference UV− vis absorption spectra in methanol, which displayed two dominant features: a moderate increase in the intensity of the nπ* band and a pronounced decrease in intensity of the low-energy part of the ππ* band. We attributed both features to increasing non-Condon effects with temperature. We show that the NEM based on the path integral molecular dynamics combined with range-separated hybrid functionals provides quantitatively accurate spectra and their differences. Experimentally, the depletion of the absorption in the ππ* band showed a characteristic vibrational progression that cannot be reproduced with the NEM. We show that hundreds of thousands of samples are necessary to achieve an accuracy sufficient for the unambiguous explanation of the observed temperature effects. We provide a detailed analysis of the temperature effects on the spectrum based on the harmonic model of the system combined with the NEM. We also rationalize the vibrational structure of the spectrum using the Franck−Condon principle.

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“…Due to the quadratic dependence with the irradiance as well as the distinct electric-dipole selection rules, the 2PA process has been extensively employed in various kinds of applications, from biology to physics. − Although in the past few years the 2PA process has been widely investigated in organic compounds because of its great technological appeal, most of these studies were concentrated in intramolecular effects, such as the electronic delocalization, degree of molecular planarity, , intramolecular charge transfer process, bond length alternation, cooperative enhancement between branches, and so on. However, there are only a few studies concerning the relationship between the 2PA processes and external effects, such as its dependence with the temperature. , This kind of study can bring important information about the relationship between the molecular structure and the electronic property of organic materials, as well as possible applications of these compounds in photonic devices. In this context, we report here the effect of temperature on the 2PA cross-section of ATβC using a white-light-continuum (WLC) Z-scan technique.…”

Section: Introductionmentioning

confidence: 99%

Temperature Effect on the Two-Photon Absorption Spectrum of All-trans-β-carotene

Vivas

Mendonça

2012

J. Phys. Chem. A

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In this report, we investigate the influence of temperature on the two-photon absorption (2PA) spectrum of all-trans-β-carotene using the femtosecond white-light-continuum Z-scan technique. We observed that the 2PA cross-section decreases quadratically with the temperature. Such effect was modeled using a three-energy-level diagram within the sum-over-essential states approach, assuming temperature dependencies to the transition dipole moment and refractive index of the solvent. The results show that the transition dipole moments from ground to excited state and between the excited states, which governed the two-photon matrix element, have distinct behaviors with the temperature. The first one presents a quadratic dependence, while the second exhibits a linear dependence. Such effects were attributed mainly to the trans→cis thermal interconversion process, which decreases the effective conjugation length, contributing to diminishing the transition dipole moments and, consequently, the 2PA cross-section.

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Azo-group dihedral angle torsion dependence on temperature: A theorerical–experimental study

Cited by 16 publications

References 33 publications

Structural and spectroscopic characterization of E- and Z-isomers of azobenzene

Structural and spectroscopic characterization of E- and Z-isomers of azobenzene

Limits of the Nuclear Ensemble Method for Electronic Spectra Simulations: Temperature Dependence of the (E)-Azobenzene Spectrum

Temperature Effect on the Two-Photon Absorption Spectrum of All-trans-β-carotene

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