Energy transfer and spatial scrambling of an exciton in a conjugated dendrimer

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Direct atomistic simulation of nonadiabatic molecular dynamics is a challenging goal that allows important insights into fundamental physical phenomena. A variety of frameworks, ranging from fully quantum treatment of nuclei to semiclassical and mixed quantum−classical approaches, were developed. These algorithms are then coupled to specific electronic structure techniques. Such diversity and lack of standardized implementation make it difficult to compare the performance of different methodologies when treating realistic systems. Here, we compare three popular methods for large chromophores: Ehrenfest, surface hopping, and multiconfigurational Ehrenfest with ab initio multiple cloning (MCE-AIMC). These approaches are implemented in the NEXMD software, which features a common computational chemistry model. The resulting comparisons reveal the method performance for population relaxation and coherent vibronic dynamics. Finally, we study the numerical convergence of MCE-AIMC algorithms by considering the number of trajectories, cloning thresholds, and Gaussian wavepacket width. Our results provide helpful reference data for selecting an optimal methodology for simulating excited-state molecular dynamics.

Section: Ehrenfest Mean Fieldmentioning

confidence: 99%

Section: Ehrenfest Mean Fieldmentioning

confidence: 99%

mentioning

confidence: 99%

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Nonadiabatic Excited-State Molecular Dynamics Methodologies: Comparison and Convergence

Freixas

White

Nelson

et al. 2021

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“…NEXMD Overview . The nonadiabatic excited state molecular dynamics (NEXMD) computational package combines the fewest switching surface hopping (FSSH) algorithm , with “on the fly” calculation of excited state energies, gradients, and nonadiabatic couplings at the configuration interaction singles (CIS) level of theory using the semiempirical Austin model 1 Hamiltonian using the Collective Electronic Oscillator (CEO) approach. − NEXMD has been previously used in a large variety of processes in multichromophore organic conjugated molecular systems like light harvesting in dendrimers, − energy transfer in donor–acceptor systems, , intramolecular energy redistribution in chorophylls, , etc …”

Section: Methodsmentioning

confidence: 99%

Back-and-Forth Energy Transfer during Electronic Relaxation in a Chlorin–Perylene Dyad

Galindo

Freixas

Tretiak

et al. 2021

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Donor−acceptor dyads represent a practical approach to tuning the photophysical properties of linear conjugated polymers in materials chemistry. Depending on the absorption wavelength, the acceptor and donor roles can be interchanged, and as such, the directionality of the energy transfer can be controlled. Herein, nonadiabatic excited state molecular dynamics simulations have been performed in an arylethylenelinked perylene−chlorin dyad. After an initial photoexcitation at the Soret band of chlorin, we observe an ultrafast sequential electronic relaxation to the lowest excited state. This process is accomplished through an efficient round-trip chlorin-to-perylene-to-chlorin energy transfer. It is characterized by successive intermittent localized and delocalized vibronic dynamics. Nonradiative relaxation takes place mainly through energy transfer events with perylene acting as a "heat sink" through which the nonradiative relaxation is efficiently funneled, and the excess energy is dispersed in a larger space of vibrational degrees of freedom. Thus, our findings suggest the use of donor−acceptor dyads as a useful strategy when one needs to deactivate an electronic excitation.

“…Thus, the dendritic macromolecules have been studied for almost 30 years. ,,,,− For example Ahn et al’s study focused on the effect of delocalized excited states on electronic energy transfer (EET) in a family of conjugated phenylacetylene (PA) light-harvesting dendrimers. In their model, the PA dendrimers can be thought of as hybrid energy-transfer structures in which limited delocalization is followed by through-space Coulombic transfer between the delocalized emitting states and the localized DPA acceptors .…”

mentioning

confidence: 99%

Delocalized Excitation or Intramolecular Energy Transfer in Pyrene Core Dendrimers

Huo

Zhao

et al. 2021

Light-harvesting and then intramolecular energy transfer are the crucial steps in natural photosynthesis. Dendrimers are one of the most promising artificial light-harvesting antennas. Insight into the relationship between molecular structure and energy transfer (or delocalized excitation) in dendrimers would help in understanding and mimicking photosynthesis. Here, a series of dendrimers T1–T4 based on pyrene as a core and fluorene/carbazole as the dendrons have been studied with time-resolved fluorescence and femtosecond transient absorption spectroscopies, revealing that the large planar structure of T1 and T2 has led to strong coupling of pyrene and fluorene units, enabling delocalized excitation over the entire molecules. But for T3 and T4, the carbazole units linking the first- and second-generation branches have broken the planar structure and suppressed the π-electron delocalization, enabling the Förster resonance energy transfer. The efficient intramolecular energy transfer from peripheral branches to the core occurs within 2 ps.