Showing papers by "Sergei Tretiak published in 2005"
TL;DR: New strategies for the rational design of NLO molecular assemblies are inferred on the basis of the acquired insights into the nature of fundamental excited-state dynamics and the nonlinear optical (NLO) response involved.
Abstract: To investigate the effect of branching on linear and nonlinear optical properties, a specific series of chromophores, epitome of (multi)branched dipoles, has been thoroughly explored by a combined theoretical and experimental approach. Excited-state structure calculations based on quantum-chemical techniques (time-dependent density functional theory) as well as a Frenkel exciton model nicely complement experimental photoluminescence and one- and two-photon absorption findings and contribute to their interpretation. This allowed us to get a deep insight into the nature of fundamental excited-state dynamics and the nonlinear optical (NLO) response involved. Both experiment and theory reveal that a multidimensional intramolecular charge transfer takes place from the donating moiety to the periphery of the branched molecules upon excitation, while fluorescence stems from an excited state localized on one of the dipolar branches. Branching is also observed to lead to cooperative enhancement of two-photon absorption (TPA) while maintaining high fluorescence quantum yield, thanks to localization of the emitting state. The comparison between results obtained in the Frenkel exciton scheme and ab initio results suggests the coherent coupling between branches as one of the possible mechanisms for the observed enhancement. New strategies for the rational design of NLO molecular assemblies are thus inferred on the basis of the acquired insights.
337 citations
TL;DR: In this article, the electronic structure and size scaling of spectroscopic observables in conjugated polymers are investigated using time-dependent density functional theory, and it is shown that local density approximations and gradient-corrected functionals do not have an effective attractive Coulomb interaction between photoexcited electron-hole pairs to form bound states and therefore do not reproduce finite exciton sizes.
Abstract: The electronic structure and size scaling of spectroscopic observables in conjugated polymers are investigated using time-dependent density functional theory. We show that local density approximations and gradient-corrected functionals do not have an effective attractive Coulomb interaction between photoexcited electron-hole pairs to form bound states and therefore do not reproduce finite exciton sizes. Long-range nonlocal and nonadiabatic density functional corrections (such as hybrid mixing with an exact Hartree-Fock exchange) are necessary to capture correct delocalization of photoexcitations in one-dimensional polymeric chains.
189 citations
TL;DR: In this paper, the excited state electronic structure of π conjugated phenylene-acetylene oligomers is calculated using time-dependent density functional theory approaches and the theoretical fluorescence spectra are analyzed in terms of Frank-Condon active nuclear normal modes and shown to compare well with experiment.
70 citations
TL;DR: First-principles quantum-chemical approaches are used to study absorption and emission properties of recently synthesized distyrylbenzene derivative chromophores and their dimers, and suggest two mechanisms for the excited-state lifetime increase in aqueous solutions.
Abstract: We use first-principles quantum-chemical approaches to study absorption and emission properties of recently synthesized distyrylbenzene (DSB) derivative chromophores and their dimers (two DSB molecules linked through a [2.2]paracyclophane moiety). Several solvent models are applied to model experimentally observed shifts and radiative lifetimes in Stokes nonpolar organic solvents (toluene) and water. The molecular environment is simulated using the implicit solvation models, as well as explicit water molecules and counterions. Calculations show that neither implicit nor explicit solvent models are sufficient to reproduce experimental observations. The contact pair between the chromophore and counterion, on the other hand, is able to reproduce the experimental data when a partial screening effect of the solvent is taken into account. Based on our simulations we suggest two mechanisms for the excited-state lifetime increase in aqueous solutions. These findings may have a number of implications for organic light-emitting devices, electronic functionalities of soluble polymers and molecular fluorescent labels, and their possible applications as biosensors and charge/energy conduits in nanoassemblies.
61 citations
TL;DR: Calculations show that both OPA and TPA spectra in the molecules studied are typically dominated by two strong peaks corresponding to different electronic states, and found that donor-acceptor strengths and conjugated bridge length have a strong impact on the cross-section magnitudes of low- and high-frequency TPA maxima.
Abstract: Time-dependent density functional theory (TD-DFT) is applied to model one-photon (OPA) and two-photon (TPA) absorption spectra in a series of conjugated cytotoxic dyes. Good agreement with available experimental data is found for calculated excitation energies and cross sections. Calculations show that both OPA and TPA spectra in the molecules studied are typically dominated by two strong peaks corresponding to different electronic states. We find that donor-acceptor strengths and conjugated bridge length have a strong impact on the cross-section magnitudes of low- and high-frequency TPA maxima, respectively. These trends are analyzed in terms of the natural transition orbitals of the corresponding electronic states. Observed structure-property relationships may have useful implications on design of organic conjugated chromophores with tunable two-photon absorption properties for photodynamic therapy applications.
53 citations
TL;DR: A semiclassical approach is applied to the scattering problem of a vibrational wave packet in the vicinity of a conical intersection of electronic energy surfaces and analytical expressions for the scattering matrix are derived.
Abstract: We apply a semiclassical approach to the scattering problem of a vibrational wave packet in the vicinity of a conical intersection of electronic energy surfaces and derive analytical expressions for the scattering matrix. The latter are valid when the scattering length that scales as square root(h) is small and a wave packet passes through the scattering region with a constant velocity. The analytical results are in excellent agreement with numerical simulations for a realistic set of parameters.
19 citations
Journal Article•
TL;DR: Piryatinski et al. as mentioned in this paper proposed a method to solve the problem of nonlinearity in a nonlinear model using the Chernyak model, which is a variant of the one proposed in this paper.
Abstract: Andrei Piryatinski,* Misha Stepanov, Sergei Tretiak, and Vladimir Chernyak Center for Nonlinear Studies, Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Institute of Automation and Electrometry, Novosibirsk 630090, Russia Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, USA (Received 18 November 2004; published 21 November 2005)
17 citations
TL;DR: In this paper, the authors investigated the combined role of branching and charge symmetry on absorption, photoluminescence and two-photon absorption (TPA) and found that a multidimensional intramolecular charge transfer takes place from the central electron-donating moiety to the periphery of the branched molecules.
Abstract: Structurally related chromophores of different symmetry (dipolar, V-shaped, octupolar) are investigated and compared for elucidation of the combined role of branching and charge symmetry on absorption, photoluminescence and two-photon absorption (TPA). Their design is based on the assembly of one, two or three π-conjugated dipolar branches on a central core. Two series of branched structures obtained from a central triphenylamine core and dipolar branches having different charge-transfer characters are investigated: photophysical properties are studied and TPA spectra are determined through two-photon excited fluorescence experiments using fs pulses in the 700-1000 nm range. Calculations based on time-dependent quantum-chemical approaches, as well as the Frenkel exciton model, complement experimental findings. Experiments and theory reveal that a multidimensional intramolecular charge transfer takes place from the central electron-donating moiety to the periphery of the branched molecules upon excitation, whereas fluorescence stems from a dipolar branch. Symmetry and inter-branch electronic coupling are found to be responsible for amplification of the TPA response of branched compounds with respect to their monomeric analogues. In particular, an enhancement is observed in regions where the TPA bands overlap, and TPA activation is obtained in spectral regions where the dipolar analogue is almost two-photon transparent. Thus, appropriate tuning of the number of branches, of the coupling between them, and modulation of intramolecular charge transfer from core to periphery open the way for substantial improvement of TPA efficiency or TPA induction in desired spectral regions.
6 citations