Femtosecond spectral evolution monitoring the bond-twisting event in barrierless isomerization in solution

Åberg, Ulf; Åkesson, Eva; Alvarez, Jose-Luis; Fedchenia, I. I.; Sundström, Villy

doi:10.1016/0301-0104(94)00022-0

Cited by 69 publications

(67 citation statements)

References 27 publications

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“…(1)-(3) has the form (4) In the absence of irradiation, P 1 = 0; therefore, this equation is reduced to the known Duffing equation for the undamped motion of a free particle in a symmetric two-well potential.…”

Section: Bifurcations In the Evolution Of Molecularmentioning

confidence: 99%

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Bifurcations in the evolution of molecular structure during photoisomerization

2005

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Photoisomerization can, in most cases, be considered as a redistribution of atoms or molecular fragments among potential wells separated by barriers in the ground electronic state of the molecule initiated by the energy of a light wave. According to catastrophe theory, this process can be irreversible as a result of the jumpwise "choice" of one or another potential well (isomer) after the molecule has shifted to a position of unstable equilibrium, i.e., at the top of a potential barrier. In Prigogine's terminology, this is an "induced bifurcation" [1].In the present work, using mixed quantum-classical simulation of the photoisomerization dynamics, we demonstrated that such jumpwise changes in the character of the evolution of molecular structure are possible when the electronic subsystem of a molecule is excited by light and part of this energy is transferred to the nuclei. These jumps can be a result of fluctuations of the parameters that characterize the light and the molecule in the vicinity of some singularities (bifurcation values), for example, as will be shown below, when the frequency of the quasi-monochromatic irradiation is changed.The evolution of the electronic subsystem of a molecule and the radiation field in time was described using quantum theory, which allowed us to correctly consider the secondary radiation field ( σ photons, see below); the nuclear subsystem was described in the framework of classical theory. Using the expression for the force exerted by the electronic subsystem of the molecule on its nuclei, which is determined by the Ehrenfest theorem, and the Schrödinger equation for the electronic subsystem and the radiation field interacting with it, we obtained a system of self-consistent differential equations for the "reaction coordinate" Q , the amplitudes b λ 0 and b σ 0 , the populations of the initial and one of the final states of the total system, and the amplitude b 01 of the population of the resonance excited state of the molecule.In the resonance approximation, this system of equations takes the form (1) where χ = λ , σ is the set of the quantum numbers of the radiation photon and the secondary photon, respectively; E 0 ( Q [ t ]) and E 1 ( Q [ t ]) are the energies of, respectively, the ground and excited electronic states, which parametrically depend on Q ; m is a constant with the dimension of mass ( m = ប / Ω ); ω 10 (the resonance detuning, which changes in time in response to the change in the isomerization coordinate Q ;where e λ and e σ are the unit vectors of the λ photon and the σ photon, respectively; d is the dipole moment operator of the molecular system (independent of Q , the Condon approximation), and N λ = 1, 2, … is the number of radiation photons; P 0 ( t ) and P 1 ( t ) are the time-dependent populations of, respectively, the ground and excited electronic states of the molecule, which are determined as follows:

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Section: Bifurcations In the Evolution Of Molecularmentioning

confidence: 99%

“…For the simplest consideration of photoisomerization, the nuclear potentials can be taken in the form (see [4,5])…”

Section: Bifurcations In the Evolution Of Molecularmentioning

confidence: 99%

Bifurcations in the evolution of molecular structure during photoisomerization

2005

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“…35 The excited-state twisting process in monomethine systems has been invoked as an example of an environmentcontrolled process with no intrinsic barrier. 21,28,[39][40][41][42][43][44] The dynamics have been described with theoretical models invoking overdamped motion. [40][41][42][43][44][45] Although the coupling of chargetransfer behavior to twisting displacements has been predicted for some time, 26 the theoretical models usually do not explicitly describe this.…”

Section: Introductionmentioning

confidence: 99%

A two-state model of twisted intramolecular charge-transfer in monomethine dyes

Olsen

McKenzie

2012

The Journal of Chemical Physics

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Articles you may be interested inModeling opto-electronic properties of a dye molecule in proximity of a semiconductor nanoparticle J. Chem. Phys. 139, 024105 (2013) A two-state model Hamiltonian is proposed, which can describe the coupling of twisting displacements to charge-transfer behavior in the ground and excited states of a general monomethine dye molecule. This coupling may be relevant to the molecular mechanism of environment-dependent fluorescence yield enhancement. The model is parameterized against quantum chemical calculations on different protonation states of the green fluorescent protein chromophore, which are chosen to sample different regimes of detuning from the cyanine (resonant) limit. The model provides a simple yet realistic description of the charge transfer character along two possible excited state twisting channels associated with the methine bridge. It describes qualitatively different behavior in three regions that can be classified by their relationship to the resonant (cyanine) limit. The regimes differ by the presence or absence of twist-dependent polarization reversal and the occurrence of conical intersections. We find that selective biasing of one twisting channel over another by an applied diabatic biasing potential can only be achieved in a finite range of parameters near the cyanine limit.

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“…These flat in the ground state molecules have several torsional degrees of freedom, and twisting of one or simultaneously several bonds may take place in the excited state. Generally, bond twisting in the excited state leads to the fast nonradiative relaxation [5][6][7][8][9], with occasional formation of nonemissive ''dark" states [10][11][12], or to the appearance of the dual fluorescence bands [13][14][15][16][17][18][19][20][21][22][23]. The dual fluorescence is a well known signature of the intramolecular charge transfer in 4-(dimethylamino)benzonitrile (DMABN) class molecules, which form twisted internal charge transfer (TICT) states involving the twisting of the amino group [14].…”

Section: Introductionmentioning

confidence: 99%