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Energy and charge transfer nonadiabatic dynamics in light-harvesting molecules and nanostructures

Periodic Reporting for period 3 - DYNAMO (Energy and charge transfer nonadiabatic dynamics in light-harvesting molecules and nanostructures)

Reporting period: 2018-06-01 to 2019-11-30

The goal of DYNAMO is to develop an efficient mixed quantum-classical theoretical methodology for the simulation of light-induced nonadiabatic processes in multichromophoric light-harvesting assemblies.
There is growing experimental evidence that nonadiabatic dynamics triggered upon light absorption plays a fundamental role in determining the efficiency of energy and charge transfer in functional materials.
In addition to the intramolecular nonradiative transitions through conical intersections, well known from photochemistry, the coupling between the chromophores in multichromophoric assemblies gives rise to novel intermolecular nonadiabatic relaxation channels through funnels between the delocalized excitonic and/or charge transfer states. In order to simulate coupled electron-nuclear dynamics in multichromophoric nanostructures the goal of DYNAMO develop and implement light-induced surface hopping methods and combine them with efficient electronic structure methods.
We apply our methodology to investigate energy and charge transport in nanostructures of self-assembled organic molecules (e.g. tubular J-aggregates), in low band-gap organic polymers (e.g. squaraines) and in hybrid plasmon-exciton architectures, where the photon capture and charge injection efficiency can be enhanced by the interaction with plasmonic fields.
The ultimate goal is to reveal mechanisms of efficient energy and charge transfer using a first principles methodology, providing guidance for the design of efficient light-harvesting systems that can be used in solar energy applications.
The main methodological achievements during the first report period include:
(i) the development and implementation of the long-range corrected tight-binding density functional theory (LC-TDDFTB) [1] and its combination with the surface hopping dynamics in the local diabatic picture.
This led to the publication of a generally applicable code DFTBaby that has been made publicly available. In parallel, we are currently implementing a new tight-binding constrained DFT (CDFT(B)) code which is currently being tested for its performance for the simulation of charge transport dynamics in large aggregates.
(ii) The second major methodological achievement involves the development of the coupled coherent state dynamics [3] that generalizes the surface hopping simulation technique and allows including quantum effects (such as e. g. Berry phase or tunnelling) in the nuclear dynamics. Currently, this method is being implemented in our in house electronic structure TD-DFTB code in order to perform full quantum dynamics simulations in model multichromophoric assemblies.
(iii) We have extended the field-induced surface hopping method (FISH) in order to simulate the coupled electron-nuclear dynamics in chiral systems driven by laser-fields with arbitrary polarization. This allowed us to propose a mechanism for the photochemical symmetry breaking in the alanine aminoacid. Our work has demonstrated theoretically that homochirality may arise in the interstellar space as a consequence of photochemical symmetry breaking.
Overall, the methodological development has proceeded according to the planned schedule so that already in the first period a number of novel applications could be realized as planned in the project part B and C. The main achievement in these two subprojects involve: (i) The theoretical design of ordered arrays of metal nanoclusters at multichromophoric templates showing that metal clusters can be used to produce ordered arrays exhibiting large excitonic coupling [5]. Such new systems could serve as plasmonically enhanced light-harvesting materials, sensors, or catalysts. We have developed a theoretical approach for the simulation of the optical properties of ordered arrays of metal clusters that is based on the ab initio parametrized Frenkel exciton model and is generally applicable. The method has been applied to self-assembled atomically precise silver clusters in one- and two-dimensional arrays on suitably designed porphyrin templates exhibiting remarkable optical properties. (ii) We have developed a fully atomistic and fully quantum-mechanical approach for the simulation of exciton dynamics and spatio-temporal plasmonic field distributions in hybrid plasmon-exciton systems by combining fully quantum simulations of the exciton dynamics with computational electrodynamics [6|. The method has been applied to simulate the functionality and to control the energy transport in devices that are formed by silver cluster self-assembly on organic templates.

[1] A. Humeniuk, R. Mitric, Long-range correction for tight-binding TD-DFT, J. Chem. Phys., 143, 134120 (2015).
[2] Lambert, F. Koch, S. F. Volker, A. Schmiedel, M. Holzapfel, A. Humeniuk, M. I. S. Röhr, R. Mitric, T. Brixner: Long-Energy transfer between squaraine polymer sections: From helix to zigzag and all the way back, J. Am. Chem. Soc. 137, 7851 (2015).
[3] A. Humeniuk, R. Mitric, Non-adiabatic dynamics around a conical intersection with surface-hopping coupled coherent states, J. Chem. Phys., 144, 234108 (2016).
[4] M. Wohlgemuth, R. Mitric, Photochemical chiral symmetry breaking in alanine, J. Phys. Chem. A, 120, 8976 (2016).
[5] M. I. S. Röhr, P. G. Lisinetskaya, R. Mitric, Excitonic properties of ordered metal nanocluster arrays at multiporphyrin templates, J. Phys. Chem. A., 120, 4465 (2016).
[6] P. G. Lisinetskaya, M. I. S. Röhr, R. Mitric, First-principles simulation of light propagation and exciton dynamics in metal cluster nanostructures, Appl. Phys. B, 122,
"The development of the efficient non-adiabatic dynamics in the frame of LC-TDDFTB has for the first time enabled us to perform fully atomistic simulations of the energy and charge transport dynamics
in large multichromophoric aggregates. In these simulations both electronic structure as well as the coupled electron-nuclear dynamics are treated from first principles in the real time.
The applications to several classes of multichromophoric assemblies has given us a full dynamical picture of the exciton transport and has revealed the time-scales of the processes such as excimer formation
which fundamentally limit exciton transport in light-harvesting materials. Furthermore, we have identified conical intersections between the excitonic states which are responsible for the efficient
nonradiative relaxation and have designed qualitative rules for their prediction in assemblies of stacked conjugated molecules. These achievements emphasise the role of the dynamical effects
in the functionality of light-harvesting materials will allow us to design novel architectures with superior properties in the future.
The development of the ""coupled coherent state"" surface hopping dynamics goes beyond the conventional surface hopping simulations by allowing to include quantum effects in the mixed quantum-classical dynamics simulations.
Such effects might be particularly important in systems where water dynamics plays an important role.
Our methods for the simulation of the coupled light-exciton propagation in plasmonic nanostructure has for the first time allowed us to treat the quantum electronic dynamics and the spatio-temporal dynamics
of the electromagnetic-field in complex nanostructure. We have shown that this methods can be used to control the light-induced function of ultrasmall plasmonic devices and have designed several new systems
that can be used for the development of new 1D and 2D plasmonic architectures.
Altogether, our methodological developments have allowed us to push the limit of the excited state non-adiabatic dynamics simulations towards complex functional materials. The improvement of the function
of such materials should lead to the development of new efficient and environment-friendly functional materials."