Interplay between structural hierarchy and exciton diffusion in artificial light harvesting

Abstract

Unraveling the nature of energy transport in multi-chromophoric photosynthetic complexes is essential to extract valuable design blueprints for light-harvesting applications. Long-range exciton transport in such systems is facilitated by a combination of delocalized excitation wavefunctions (excitons) and exciton diffusion. The unambiguous identification of the exciton transport is intrinsically challenging due to the system’s sheer complexity. Here we address this challenge by employing a spectroscopic lab-on-a-chip approach: ultrafast coherent two-dimensional spectroscopy and microfluidics working in tandem with theoretical modeling. We show that at low excitation fluences, the outer layer acts as an exciton antenna supplying excitons to the inner tube, while under high excitation fluences the former converts its functionality into an exciton annihilator which depletes the exciton population prior to any exciton transfer. Our findings shed light on the excitonic trajectories across different sub-units of a multi-layered artificial light-harvesting complex and underpin their great potential for directional excitation energy transport.

Structural characterization of supramolecular hollow nanotubes with atomistic simulations and SAXS

“…Cryo-TEM has been proven particularly useful working hand in hand with exciton theory/spectral calculations and MD simulations by providing constraints on the characteristic sizes and geometry of such system. 19,26,29,48 The distinct double-peak modulation of the cross-sectional profile extracted from cryo-TEM images clearly resolves the nanotubes' structure, comprising the inner and outer concentric tubes. At the same time, the objects remain as close as possible to their native state, thanks to the fast freezing that prevents the emergence of artifacts due to the temperature change.…”

“…The instrument is built on a Cu rotating anode providing a high flux X-ray beam of wavelength lambda = 1.5413 Ang. The samples were prepared according to the protocol described in Kriete et al 48 In order to cover a wide angular range, two different SAXS patterns were acquired per each sample using two different sample-todetector (S-to-D) distances, 240 mm and 3100 mm respectively. The SAXS patterns were acquired using two Bruker Vantec detectors.…”

“…[55][56][57] To validate further our simulation results, we conducted SAXS experiments to characterize the structural features of C8S3 nanotubes in water/methanol solution. 48 The obtained SAXS spectra were compared to MD simulated spectra 55 from short C8S3 nanotubes with different dimensions that are reported in Table S7 of the ESI. † The experimental spectrum was also compared to a number of simple models for the electron density distribution in tubular assemblies (Fig.…”

From wavelike to sub-diffusive motion: exciton dynamics and interaction in squaraine copolymers of varying length

“…This technique facilitates a direct observation of exciton-exciton interactions. [48][49][50] In EEI2D, exciton-exciton annihilation is observable in the evolution of the signal amplitude as a function of population time. This technique can therefore be used not only to study EEI, but one can utilize the annihilation as a tool to probe single-exciton propagation dynamics even in the absence of spectral changes during transport.…”

Molecular Dynamics of Bioinspired Nanotubes

“…The experimental spectrum was also compared to a number of simple models for the electron density distribution in tubular assemblies, Figure 2.10. The scattering curve of the C8S3 nanotubes prepared via the alcoholic route [76] shows a decaying trend with the scattering vector q, characterized by several oscillations characteristic for the size of self-assembled objects. The decay of the intensity in the low q region (q < 0.5 nm −1 ) is typical for long anisotropic objects, in agreement with the long nanotubes observed by cryo-TEM [41,43,44,45,46], Figure 2.10a.…”