Effect of conformational disorder on exciton states of an azobenzene aggregate

2023

Preprint

Molecular photoswitches are a promising class of molecules for development of new functional, light-controlled materials. In complex systems, composed of multiple photoswitchable units, photophysical and photochemical properties may be altered as compared to isolated chromophores. And phenomena such as excitation energy transfer may arise in the aggregated state. In the present work, using nonadiabatic molecular dynamics simulations in conjunction with transition density matrix analysis, we study exciton dynamics in H-type tetramers of azobenzene, a prototypical molecular switch. We consider “free” and “constrained” (embedded in an environment of additional azobenzene molecules) models with different intermolecular distances (3.5 and 5.5 Å). Our simulations reveal ultrafast exciton localization upon ππ* excitation, occurring on a sub-100 fs timescale, and proceeding faster for the longer separation distance than for the shorter one. We also find that exciton transfer takes place during excited state dynamics in the ππ* manifold but it is strongly inhibited in the nπ* manifold. Moreover, we find that the ππ* trans→cis isomerization quantum yields are lower by a factor of about three for free / not strongly constrained tetramers than for the monomer, and no switching is observed for the most tightly packed model.

Section: Resultssupporting

confidence: 88%

Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 97%

Section: Models and Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Exciton localization and transfer in azobenzene aggregates: A surface hopping molecular dynamics study

2023

Preprint

“…Finally, it should be mentioned that the (de)localization of the exciton states is affected by conformational disorder, as was demonstrated for an azobenzene tetramer in our recent work. 84 Ultimately, the photoinduced dynamics may lead to further changes in (de)localization and result in exciton transfer between monomers, as was reported very recently by Sangiogo Gil et al, based on surface hopping calculations employing an exciton model. 85…”

Section: Discussionmentioning

confidence: 78%

Exciton states of azobenzene aggregates: A first-principles study

Beqiraj

2022

Preprint

Interaction between azobenzene-containing molecules in supramolecular structures or self-assembled monolayers (SAMs) results in the formation of molecular exciton states. These states determine photophysical and photochemical processes in such assemblies. Here, using first-principles quantum chemical calculations, we study optical spectra and exciton delocalization of the exciton states in model clusters of azobenzene molecules. Specifically, we consider one-dimensional linear chains and two-dimensional SAM-like arrangements, and compute the exciton states by means of time-dependent long-range corrected density functional theory (TD-lc-DFT) and ab initio configuration interaction singles (CIS), for clusters including up to 18 azobenzene molecules. We analyze the nature of the exciton states using transition density matrix analysis. In addition, we make a connection to periodic systems applying the Bethe–Salpeter equation (BSE) / Green’s function many-body perturbation theory (GW) approach to a selected system. We find that the brightest excitons are dominated by local excitations. The energetic location of charge transfer states in the electronic spectra of aggregates depends to a large extent on a given method and distance between nearest neighbours. Furthermore, we analyze how an excitonic delocalization pattern changes with varying molecular orientation in the unit cell of SAMs.

Exciton States of Azobenzene Aggregates: A First‐Principles Study

Beqiraj

2023

Advcd Theory and Sims

Self Cite

Interaction between azobenzene-containing molecules in supramolecular structures or self-assembled monolayers (SAMs) results in the formation of molecular exciton states. These states determine photophysical and photochemical processes in such assemblies. Here, using first-principles quantum chemical calculations, optical spectra and exciton delocalization of the exciton states in model clusters of azobenzene molecules are studied. Specifically, 1D linear chains and 2D SAM-like arrangements are considered, and the exciton states are computed by means of time-dependent long-range corrected density functional theory (TD-lc-DFT) and ab initio configuration interaction singles (CIS), for clusters including up to 18 azobenzene molecules. The nature of the exciton states is analyzed using transition density matrix analysis. In addition, a connection to periodic systems is made applying the Bethe-Salpeter equation (BSE)/Green's function many-body perturbation theory (GW) approach to a selected system. It is found that the brightest excitons are dominated by local excitations. The energetic location of charge transfer states in the electronic spectra of aggregates depends to a large extent on a given method and distance between nearest neighbors. Furthermore, it is analized how an excitonic delocalization pattern changes with varying molecular orientation in the unit cell of SAMs.