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Wepresent a new, fully ab initio approach for computing intramolecularcharge- and energy-transfer rates. Using a time-convolutionless masterequation approach and parametrizing using couplings obtained usingan accurate quantum chemical approach, we benchmark the approach againstexperimental results and Marcus theory rates for triplet energy transferfor a series of donor–bridge–acceptor systems. An importantcomponent of our analysis is the use of a projection operator schemethat parses out specific internal nuclear motions that accompany theelectronic transition. Using an iterative Lanczos approach, we concentratethe coupling between the electronic and nuclear degrees of freedominto a small number of reduced harmonic modes. We find that by usingonly a single reduced mode termed the “primary mode”,one obtains an accurate evaluation of the golden rule rate constantand insight into the nuclear motions responsible for coupling theinitial and final electronic states. In particular, the primary modereflects the irreducible representation of the donor and acceptorexcited states. [ABSTRACT FROM AUTHOR]

We present a first principles theory of exciton diffusionin conformationally disordered conjugated polymers. Central to ourtheory is that exciton transfer occurs from vibrationally relaxedstates (VRSs) to local exciton ground states (LEGSs). LEGSs are determinedby the diagonal and off-diagonal disorder induced by static densityand torsional fluctuations, and VRSs are further localized by exciton–phononcoupling. The theory is implemented using the Frenkel–Holsteinmodel to calculate the wave functions and energies of the LEGSs andVRSs. The coupling of VRSs and LEGSs via long-range dipole–dipoleinteractions leads to the familiar line-dipole approximation for theexciton transfer integral. The exciton transfer rates are derivedfrom the Fermi Golden rule. The theory is applied to an ensemble ofconformationally disordered poly(p-phenylenevinylene)chains using a kinetic Monte Carlo algorithm. The following are shown:(i) Torsional disorder and trans–cis defects reduce the excitondiffusion length. (ii) Radiative recombination occurs from VRSs inthe tail of their density of states. (iii) Torsional disorder increasesthe band gap, the line width of the density of states, and the Stokesshift. As a consequence, it causes a blue shift in the vertical absorption,but a red shift in the emission. (iv) The energy of the radiated photondecreases as −log t, with a gradientthat increases with torsional disorder. The predicted exciton diffusionlengths of ∼8–11 nm are in good agreement with experimentalvalues. [ABSTRACT FROM AUTHOR]

Abstract: We consider here a model for the transport of a self-trapped exciton on a lattice under thermal bias in order to develop a quantum mechanical theory for vibrational energy transport along a molecular wire that is in contact with thermal reservoirs at either end of the molecule. For the specific case of the migration of a Conal excitation along a poly-amide α-helix, we find that within our model a Conal exciton can become self-trapped due to strong hydrogen bonding interactions with amide groups even at physiologically relevant temperatures. Furthermore, we find that under the non-equilibrium condition in which the temperature of the two baths are different, the self-trapped state will diffuse towards the cooler end with a diffusion constant proportional to the average temperature of the lattice and a drift proportional to the temperature gradient . [Copyright &y& Elsevier]

Abstract: Time-dependent density functional theory (TD-DFT) is used to examine the effect of stacking in a model semiconducting polymer hetrojunction system consisting of two co-facially stacked oligomers. We find that the excited electronic states are highly sensitive to the alignment of the monomer units of the two chains. In the system we examined, the exchange energy is nearly identical to both the and band off-set at the heterojunction and to the exciton binding energy. Our results indicate that the triplet excitonic states are nearly degenerate with the singlet exciplex states opening the possibility for the interconversion of singlet and triplet electronic states at the heterojunction interface via spin–orbit coupling localized on the heteroatoms. Using Russell–Saunders theory, we estimate this interconversion rate to be approximately 700–800ps, roughly a 5–10-fold increase compared to isolated organic polymer chains. [Copyright &y& Elsevier]

Abstract: Recent ultrafast experiments have implicated intrachain base-stacking rather than base-pairing as the crucial factor in determining the fate and transport of photoexcited species in DNA chains. An important issue that has emerged concerns whether or not a Frenkel excitons is sufficient one needs charge-transfer states to fully account for the dynamics. Here we present an SU(2)⊗ SU(2) lattice model which incorporates both intrachain and interchain electronic interactions to study the quantum mechanical evolution of an initial excitonic state placed on either the adenosine or thymidine side of a model B DNA poly(dA).poly(dT) duplex. Our calculations indicate that over several hundred femtoseconds, the adenosine exciton remains a cohesive excitonic wave packet on the adenosine side of the chain where as the thymidine exciton rapidly decomposes into mobile electron/hole pairs along the thymidine side of the chain. In both cases, the very little transfer to the other chain is seen over the time-scale of our calculations. We attribute the difference in these dynamics to the roughly 4:1 ratio of hole versus electron mobility along the thymidine chain. We also show that this difference is robust even when structural fluctuations are introduced in the form of static off-diagonal disorder. [Copyright &y& Elsevier]

Explores the quantum trajectories and adaptive grids techniques as possible solution to quantum mechanics' hydrodynamical equations, facilitating the design of computational methods to predict system evolution. Implementation of the hydrodynamic equations; Grid adaptation using the monitor function; Application of dynamic grid algorithms.

A typographical error was made on page 054103-7 in Eq. (50). The integral over "d I i " on the RHS of the equation should be "d I W i SB I i sb ." Erratum: "Stochastic exciton-scattering theory of optical line shapes: Renormalized many-body contributions" [J. Chem. Phys. [Extracted from the article]

The article features research on the use of complex organic molecules in semi-conductor devices. Forecasting the properties of complex organic molecules is subject to limitations. By constructing a model of their behavior, in a series of scattering vertices, it is possible to make accurate calculations of their excited state. The method could be employed in the development of new light harvesting materials based on organic conjugated polymer materials.

We develop a stochastic theory that treats time-dependent exciton–exciton s-wave scattering and that accounts for dynamic Coulomb screening, which we describe within a mean-field limit. With this theory, we model excitation-induced dephasing effects on time-resolved two-dimensional coherent optical lineshapes and we identify a number of features that can be attributed to the many-body dynamics occurring in the background of the exciton, including dynamic line narrowing, mixing of real and imaginary spectral components, and multi-quantum states. We test the model by means of multidimensional coherent spectroscopy on a two-dimensional metal-halide semiconductor that hosts tightly bound excitons and biexcitons that feature strong polaronic character. We find that the exciton nonlinear coherent lineshape reflects many-body correlations that give rise to excitation-induced dephasing. Furthermore, we observe that the exciton lineshape evolves with the population time over time windows in which the population itself is static in a manner that reveals the evolution of the multi-exciton many-body couplings. Specifically, the dephasing dynamics slow down with time, at a rate that is governed by the strength of exciton many-body interactions and on the dynamic Coulomb screening potential. The real part of the coherent optical lineshape displays strong dispersive character at zero time, which transforms to an absorptive lineshape on the dissipation timescale of excitation-induced dephasing effects, while the imaginary part displays converse behavior. Our microscopic theoretical approach is sufficiently flexible to allow for a wide exploration of how system-bath dynamics contribute to linear and non-linear time-resolved spectral behavior. [ABSTRACT FROM AUTHOR]