Femtosecond solvation dynamics of water

Jimenez, Ralph; Fleming, Graham R.; Kumar, P. V.; Maroncelli, Mark

doi:10.1038/369471a0

Cited by 1,251 publications

(1,509 citation statements)

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“…A considerable part of decay is not diffusive but rather inertial. [28][29][30][31] The initial relaxation, being inertial in nature, is described with a Gaussian autocorrelation function x 1 e -(t/τ 1 ) 2 . In this case, the solvent relaxation function becomes X(t) ) x 1 e -(t/τ 1 ) 2 + ∑ 2 N x i e -t/τ i.…”

Section: The Modelmentioning

confidence: 99%

Solvent and Spectral Effects in the Ultrafast Charge Recombination Dynamics of Excited Donor−Acceptor Complexes

Feskov¹,

Ionkin²,

Ivanov³

et al. 2008

J. Phys. Chem. A

132

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The charge recombination dynamics of excited donor-acceptor complexes consisting of hexamethylbenzene (HMB), pentamethylbenzene (PMB), and isodurene (IDU) as electron donors and tetracyanoethylene (TCNE) as electron acceptor in various polar solvents has been investigated within the framework of the stochastic approach. The model accounts for the reorganization of intramolecular high-frequency vibrational modes as well as for the solvent reorganization. All electron-transfer energetic parameters have been determined from the resonance Raman data and from the analysis of the stationary charge transfer absorption band, while the electronic coupling has been obtained from the fit to the charge recombination dynamics in one solvent. It appears that nearly 100% of the initially excited donor-acceptor complexes recombine in a nonthermal (hot) stage when the nonequilibrium wave packet passes through a number of term crossings corresponding to transitions toward vibrational excited states of the electronic ground state. Once all parameters of the model have been obtained, the influence of the dynamic solvent properties (solvent effect) and of the carrier frequency of the excitation pulse (spectral effect) on the charge recombination dynamics have been explored. The main conclusions are (i) the model provides a globally satisfactory description for the IDU/TCNE complex although it noticeably overestimates the spectral effect, (ii) the solvent effect is quantitatively well described for the PMB/TCNE and HMB/TCNE complexes but the model fails to reproduce their spectral effects, and (iii) the positive spectral effect observed with the HMB/TCNE complex cannot be described within the framework of two-level models and the charge redistribution in the excited complexes should most probably be taken into account.

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Section: The Modelmentioning

confidence: 99%

Solvent and Spectral Effects in the Ultrafast Charge Recombination Dynamics of Excited Donor−Acceptor Complexes

Feskov¹,

Ionkin²,

Ivanov³

et al. 2008

J. Phys. Chem. A

132

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“…Such phenomena have been widely investigated by experiments [13][14][15][16][17][18] and by molecular simulations [19][20][21][22][23][24][25][26] for water in biological systems such as proteins and DNA.…”

Section: Introductionmentioning

confidence: 99%

Dynamics and Thermodynamics of Water in PAMAM Dendrimers at Subnanosecond Time Scales

2005

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Atomistic molecular dynamics simulations are used to study generation 5 polyamidoamine (PAMAM) dendrimers immersed in a bath of water. We interpret the results in terms of three classes of water: buried water well inside of the dendrimer surface, surface water associated with the dendrimer-water interface, and bulk water well outside of the dendrimer. We studied the dynamic and thermodynamic properties of the water at three pH values: high pH with none of the primary or tertiary amines protonated, intermediate pH with only the primary amines protonated, and low pH with all amines protonated. For all pH values we find that both buried and surface water exhibit two relaxation times: a fast relaxation (∼1 ps) corresponding to the libration motion of the water and a slow (∼20 ps) diffusional component related to the escaping of water from one domain to another. In contrast for bulk water the fast relaxation is ∼0.4 ps while the slow relaxation is ∼14 ps. These results are similar to those found in biological systems, where the fast relaxation is found to be ∼1 ps while the slow relaxation ranges from 20 to 1000 ps. We used the 2PT MD method to extract the vibrational (power) spectrum and found substantial differences for the three classes of water. The translational diffusion coefficient for buried water is 11-33% (depending on pH) of the bulk value while the surface water is about 80%. The change in rotational diffusion is quite similar: 21-45% of the bulk value for buried water and 80% for surface water. This shows that translational and rotational dynamics of water are affected by the PAMAM-water interactions as well as due to the confinement in the interior of the dendrimer. We find that the reduction of translational or rotational diffusion is accompanied by a blue shift of the corresponding libration motions (∼10 cm -1 for translation, ∼35 cm -1 for rotation), indicating higher local force constants for these motions. These effects are most pronounced for the lowest pH, probably because of the increased rigidity caused by the internal charges. From the vibrational density of states we also calculate the enthalpies and entropies of the various waters. We find that water molecules are enthalpically favored near the PAMAM dendrimer: energy for surface water is ∼0.1 kcal/mol lower to that in the bulk, and ∼0.5-0.9 kcal/mol lower for buried water. In contrast, we find that both the buried and surface water are entropically unfavored: buried water is 0.9-2.2 kcal/mol lower than the bulk while the surface water is 0.1-0.2 kcal/mol lower. The net result is a thermodynamically unfavored state of the water surrounding the PAMAM dendrimer: 0.4-1.3 kcal/mol higher for buried water and 0.1-0.2 kcal/mol for surface water. This excess free energy of the surface and buried waters is released when the PAMAM dendrimer binds to DNA or metal ions, providing an extra driving force.

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“…The shifts calculated using both methods 1 and 2 are in very good agreement with the full ab initio values. The same is true for the water dimer shown in Table 2, dimethyl sulphoxide(H 2 O) 4 in Table 3, and CH 3 SOCH 3 (H 2 O) 14 in Table 4. In all examples, the errors are on the order of a few hundredths of an eV.…”

Section: Methodsmentioning

confidence: 60%

“…Several examples are used to test the CIS/EFP1 method, a water dimer (H 2 O(H 2 O)), formaldehyde with 1 water (HCHO(H 2 O)), dimethyl sulphoxide in 4 waters (CH 3 SOCH 3 (H 2 O) 4 ), and dimethyl sulphoxide in 14 waters (CH 3 SOCH 3 (H 2 O) 14 ). The solute molecules in these examples are treated using the CIS method, and the water molecules are described with the EFP1/HF method.…”

Section: Methodsmentioning

confidence: 99%

“…[5][6][7][8] Therefore, coumarins are widely used as a tool to investigate the solute-solvent interactions and solvation dynamics. 4,[9][10][11][12] For example, recently, coumarin 153 has been used as a probe to study solvent dynamics in proteins by time-dependent fluorescence Stokes shift 13 measurements. 14 In order to understand the effects of polarity and the H-bonding of the solvents on the electronic spectrum of coumarin 120, a study by Zhao et al using TDDFT 15,16 (time-dependent density functional theory) with the PCM 17 (polarizable continuum model) for solvents was performed.…”

Section: Introductionmentioning

confidence: 99%

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Solvent-Induced Frequency Shifts: Configuration Interaction Singles Combined with the Effective Fragment Potential Method

et al. 2010

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The simplest variational method for treating electronic excited states, configuration interaction with single excitations (CIS), has been interfaced with the effective fragment potential (EFP) method to provide an effective and computationally efficient approach for studying the qualitative effects of solvents on the electronic spectra of molecules. Three different approaches for interfacing a non-self-consistent field (SCF) excited-state quantum mechanics (QM) method and the EFP method are discussed. The most sophisticated and complex approach (termed fully self consistent) calculates the excited-state electron density with fully self-consistent accounting for the polarization (induction) energy of effective fragments. The simplest approach (method 1) includes a strategy that indirectly adds the EFP perturbation to the CIS wave function and energy via modified Hartree−Fock molecular orbitals, so that there is no direct EFP interaction with the excited-state density. An intermediate approach (method 2) accomplishes the latter in a noniterative perturbative manner. Theoretical descriptions of the three approaches are presented, and test results of solvent-induced shifts using methods 1 and 2 are compared with fully ab initio values. These comparisons illustrate that, at least for the test cases examined here, modification of the ground-state Hartree−Fock orbitals is the largest and most important factor in the calculated solvent-induced shifts. Method 1 is then employed to study the aqueous solvation of coumarin 151 and compared with experimental measurements. PO Box 2206, Germantown, Maryland 20875 ReceiVed: February 27, 2010 ReVised Manuscript ReceiVed: May 20, 2010 The simplest variational method for treating electronic excited states, configuration interaction with single excitations (CIS), has been interfaced with the effective fragment potential (EFP) method to provide an effective and computationally efficient approach for studying the qualitative effects of solvents on the electronic spectra of molecules. Three different approaches for interfacing a non-self-consistent field (SCF) excited-state quantum mechanics (QM) method and the EFP method are discussed. The most sophisticated and complex approach (termed fully self consistent) calculates the excited-state electron density with fully self-consistent accounting for the polarization (induction) energy of effective fragments. The simplest approach (method 1) includes a strategy that indirectly adds the EFP perturbation to the CIS wave function and energy via modified Hartree-Fock molecular orbitals, so that there is no direct EFP interaction with the excited-state density. An intermediate approach (method 2) accomplishes the latter in a noniterative perturbative manner. Theoretical descriptions of the three approaches are presented, and test results of solvent-induced shifts using methods 1 and 2 are compared with fully ab initio values. These comparisons illustrate that, at least for the test cases examined here, modification of the groun...

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Femtosecond solvation dynamics of water

Cited by 1,251 publications

References 27 publications

Solvent and Spectral Effects in the Ultrafast Charge Recombination Dynamics of Excited Donor−Acceptor Complexes

Solvent and Spectral Effects in the Ultrafast Charge Recombination Dynamics of Excited Donor−Acceptor Complexes

Dynamics and Thermodynamics of Water in PAMAM Dendrimers at Subnanosecond Time Scales

Solvent-Induced Frequency Shifts: Configuration Interaction Singles Combined with the Effective Fragment Potential Method

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