Time-resolved circular dichroism of excitonic systems: theory and experiment on an exemplary squaraine polymer

Ress, Lea; Malý, Pavel; Landgraf, Jochen; Lindorfer, Dominik; Hofer, Michaël; Selby, Joshua; Lambert, Christoph; Renger, Thomas; Brixner, Tobias

doi:10.1039/d3sc01674a

Cited by 6 publications

(5 citation statements)

References 85 publications

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“…Such pump-induced LD can couple with stray LB of the optics before the sample, and transient contributions arising from this effect may overlap with the TrCD signal 42 . Indeed, this could be the reason why some of our previously recorded TrCD spectra employing a pump beam with linear polarisation for thin-film samples of opposite chirality did not resemble a perfect mirror symmetry 24 , despite the fact that they were carried out at the “magic angle” condition for TrCD spectroscopy 43 – 45 .…”

Section: Resultsmentioning

confidence: 98%

Annealing temperature-dependent induced supramolecular chiroptical response of copolymer thin films studied by pump-modulated transient circular dichroism spectroscopy

Gust,

Scholz,

Schumacher

et al. 2024

Sci Rep

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Copolymer thin films showing induced supramolecular chirality are of considerable interest for optoelectronic applications such as organic light-emitting diodes. Here, we introduce a new helicene-like chiral additive with two octyloxy substituents which displays excellent chiral induction properties in an achiral polyfluorene copolymer, leading to a circular dichroism (CD) response of up to 10,000 mdeg. This chiral inducer also displays very good thermal stability, which enables us to perform an extended study on the induced chiroptical properties of the cholesteric copolymer thin films annealed at different temperatures in the range 140–260 °C. Starting from about 180 °C, a distinct change in the morphology of the CD-active film is observed by CD microscopy, from micrometre-size granular to extended CD-active regions, where the latter ones display skewed distributions of the dissymmetry parameter gabs. Broadband Müller matrix spectroscopy finds a pronounced CD and circular birefringence (CB) response and only weak linear dichroism (LD, LD’) and linear birefringence (LB, LB’). Ultrafast transient CD spectroscopy with randomly polarised excitation reveals a clean mirror-image-type transient response, which shows a second-order decay of the S1 population due to singlet–singlet annihilation processes.

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Section: Resultsmentioning

confidence: 98%

Annealing temperature-dependent induced supramolecular chiroptical response of copolymer thin films studied by pump-modulated transient circular dichroism spectroscopy

Gust,

Scholz,

Schumacher

et al. 2024

Sci Rep

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show abstract

“…An exact treatment of the response of the system requires consideration of contributions from all elements of the density matrix. However, for delay times longer than vibrational relaxation, it is reasonable to ignore the response contributions of coherences and compute only the sequential contribution to the signal, as customarily done. − …”

Section: Methods and Computational Detailsmentioning

confidence: 99%

Insights into Energy Transfer in Light-Harvesting Complex II Through Machine-Learning Assisted Simulations

Betti,

Saraceno,

Cignoni

et al. 2024

J. Phys. Chem. B

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Light-harvesting complex II (LHCII) is the major antenna of higher plants. Energy transfer processes taking place inside its aggregate of chlorophylls have been experimentally investigated with time-resolved techniques, but a complete understanding of the most relevant energy transfer pathways and relative characteristic times remains elusive. Theoretical models to disentangle experimental data in LHCII have long been challenged by the large size and complex nature of the system. Here, we show that a fully first-principles approach combining molecular dynamics and machine learning can be successfully used to reproduce transient absorption spectra and characterize the EET pathways and the involved times.

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“…47 Furthermore, we neglect the coherent term of the response, and compute only the sequential term, which is related to population evolution during the waiting time t 2 . 47 This approximation has been commonly used for TA simulations of multichromophoric systems, 9,11,13,46,48 and corresponds to assuming that vibrational relaxation is much faster than the delay time t 2 between the pump and the probe. 46 The third-order transient absorption signal at a probe frequency ω can be expressed as a sum of ground-state bleaching (GSB), stimulated emission (SE), and excited-state absorption (ESA):…”

Section: Transient Absorption Spectramentioning

confidence: 99%

“…The window response functions for each exciton can be written directly in the frequency domain, where we ignore the pulse shape for the probe pulse. The doorway population of exciton a created by the pump pulse is determined by the overlap between the pump and the absorption spectrum of exciton a 48,49 :…”

Section: Transient Absorption Spectramentioning

confidence: 99%

First-principles simulation of excitation energy transfer and transient absorption spectroscopy in the CP29 light-harvesting complex

Saraceno,

Sláma,

Cupellini

2023

The Journal of Chemical Physics

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The dynamics of delocalized excitons in light-harvesting complexes (LHCs) can be investigated using different experimental techniques, and transient absorption (TA) spectroscopy is one of the most valuable methods for this purpose. A careful interpretation of TA spectra is essential for the clarification of excitation energy transfer (EET) processes occurring during light-harvesting. However, even in the simplest LHCs, a physical model is needed to interpret transient spectra as the number of EET processes occurring at the same time is very large to be disentangled from measurements alone. Physical EET models are commonly built by fittings of the microscopic exciton Hamiltonians and exciton-vibrational parameters, an approach that can lead to biases. Here, we present a first-principles strategy to simulate EET and transient absorption spectra in LHCs, combining molecular dynamics and accurate multiscale quantum chemical calculations to obtain an independent estimate of the excitonic structure of the complex. The microscopic parameters thus obtained are then used in EET simulations to obtain the population dynamics and the related spectroscopic signature. We apply this approach to the CP29 minor antenna complex of plants for which we follow the EET dynamics and transient spectra after excitation in the chlorophyll b region. Our calculations reproduce all the main features observed in the transient absorption spectra and provide independent insight on the excited-state dynamics of CP29. The approach presented here lays the groundwork for the accurate simulation of EET and unbiased interpretation of transient spectra in multichromophoric systems.

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Time-resolved circular dichroism of excitonic systems: theory and experiment on an exemplary squaraine polymer

Abstract: Experimental and theoretical foundations for femtosecond time-resolved circular dichroism (TRCD) spectroscopy of excitonic systems are presented. In this method, the system is pumped with linearly polarized light and the signal...

Cited by 6 publications

References 85 publications

Annealing temperature-dependent induced supramolecular chiroptical response of copolymer thin films studied by pump-modulated transient circular dichroism spectroscopy

Annealing temperature-dependent induced supramolecular chiroptical response of copolymer thin films studied by pump-modulated transient circular dichroism spectroscopy

Insights into Energy Transfer in Light-Harvesting Complex II Through Machine-Learning Assisted Simulations

First-principles simulation of excitation energy transfer and transient absorption spectroscopy in the CP29 light-harvesting complex

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