Supramolecular assemblies that interact with light have recently garnered much interest as well-defined nanoscale materials for electronic excitation energy collection and transport. However, to control such complex systems it is essential to understand how their various parts interact and whether these interactions result in coherently shared excited states (excitons) or in diffusive energy transport between them. Here, we address this by studying a model system consisting of two concentric cylindrical dye aggregates in a light-harvesting nanotube. Through selective chemistry we are able to unambiguously determine the supramolecular origin of the observed excitonic transitions. These results required the development of a new theoretical model of the supramolecular structure of the assembly. Our results demonstrate that the two cylinders of the nanotube have distinct spectral responses and are best described as two separate, weakly coupled excitonic systems. Understanding such interactions is critical to the control of energy transfer on a molecular scale, a goal in various applications ranging from artificial photosynthesis to molecular electronics.

Uniform exciton fluorescence from individual molecular nanotubes immobilized on solid substrates Eisele, Doerthe M.; Knoester, Jasper; Kirstein, Stefan; Rabe, Juergen P.; Vanden Bout, David A.; Rabe, Jürgen P. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Since the optical properties of the tubular J-aggregates strongly depend on their specific supramolecular structure, the absorption and emission spectra from the sample can be used to determine if the molecular structure of the aggregates has changed upon deposition onto the substrate. Because the tubules on the substrate are highly dilute, emission spectra rather than the very weak absorption spectra were used. Emission spectra were collected rather than excitation spectra because of the extremely small Stokes shift for the emission. Emission spectra of tubular J-aggregates in solution (red) and after preparation on a quartz surface (black)via spin-coating and slowly drying in air (c) Idem, but now the black line is the spectrum of aggregates prepared on quartz via the drop flow technique and drying by blowing with nitrogen.As shown in the manuscript, the sample prepared by the drop-flow technique and carefully dried in air in a black box had spectra that were nearly identical in both position and width to the solution, indicating no significant morphological and structural changes upon deposition.3

ABSTRACT:We report 1.6 ± 1 μm exciton transport in self-assembled supramolecular light-harvesting nanotubes (LHNs) assembled from amphiphillic cyanine dyes. We stabilize LHNs in a sucrose glass matrix, greatly reducing light and oxidative damage and allowing the observation of exciton− exciton annihilation signatures under weak excitation flux. Fitting to a onedimensional diffusion model, we find an average exciton diffusion constant of 55 ± 20 cm 2 /s, among the highest measured for an organic system. We develop a simple model that uses cryogenic measurements of static and dynamic energetic disorder to estimate a diffusion constant of 32 cm 2 /s, in agreement with experiment. We ascribe large exciton diffusion lengths to low static and dynamic energetic disorder in LHNs. We argue that matrix-stabilized LHNS represent an excellent model system to study coherent excitonic transport. KEYWORDS: J-aggregate, molecular aggregate, exciton, exciton diffusion, coherent exciton, exciton delocalization E xcitons are bound electron−hole pairs generated upon absorption of a photon or through charge carrier injection. Photosynthetic organisms and organic electronics make use of ordered molecular aggregates as excitonic antennas, with energy transport out-competing radiative and nonradiative decay channels leading to near-unity internal quantum efficiencies. 1,2 Like electronic conduction, molecular exciton conduction falls largely in two regimes: hopping and delocalization. In the hopping regime, interaction with the environment (the reorganization energy) exceeds the dipole−dipole coupling (λ reorg > J), leading to Forster resonance dominated transport. In the delocalized regime, dipole−dipole coupling exceeds the reorganization energy leading to Redfield transport. 3,4 Efficient conduction of spin-singlet excitons requires a balance of these two regimes, with both coherent quantum delocalization and incoherent resonance energy transfer playing a role in natural and artificial light-harvesting systems. 3,5−7 However, extracting principles of design from disordered complex biological and polymer systems is a significant challenge. 8 This study probes singlet exciton transport in self-assembled light harvesting nanotubes (LHNs). LHNs are quasi one-dimensional Jaggregates consisting of ordered amphiphillic cyanine dyes that form extended transition dipoles with concentrated oscillator strength in a lower-energy, highly emissive state. 9 LHNs show remarkably high overall coupling, negligible reorganization energies, and high structural uniformity resulting in large delocalization lengths. LHNs are an excellent model material for exploring the relationship between quantum delocalization and energy transport in a system where λ reorg ≪ J (coherent regime). 10−12 However, spectroscopic studies of LHNs have been hampered by difficulties in sample preparation 13 and photoinstability. 14 As a result, studies of exciton transport in LHNs have yielded highly variable results, 15−17 with estimates of transport ranging from 30 to 300 nm ...

The amphiphilic cyanine dye 3,3′-bis(2-sulfopropyl)-5,5′,6,6′-tetrachloro-1,1′-dioctylbenzimidacarbocyanine (C8S3) self-assembles in aqueous solution to form double-walled, tubular J-aggregates with ∼13 nm diameters and lengths up to several hundred nanometers. The redox and light absorption properties of immobilized J-aggregates on transparent, conductive indium tin oxide (ITO) electrodes have been studied directly using cyclic voltammetry (CV) in conjunction with UV-vis spectroscopy to elucidate unique mechanistic features of J-aggregate oxidation. Morphological properties were examined using in situ atomic force microscopy (AFM). Irreversible J-aggregate oxidation appears to occur primarily along the outer wall of the tubular structure as evidenced by the potential-induced irreversible bleaching of J-band absorption. Voltammetric studies as a function of scan rate and pH indicate that J-aggregate oxidation involves both electrochemical and chemical steps in which dimerization and subsequent dehydrogenation of the J-aggregate leads to the formation of a new dehydrogenated dimer oxidation product. This dehydrogenated dimer exhibits an absorbance band near 560 nm along with a reversible reduction peak characteristic of a surface-confined, redox-active species. Excellent correlation of J-aggregate redox potentials with spectroelectrochemical data is obtained that allows us to understand energetic thresholds for electron transfer in C8S3 tubular J-aggregates.

Graphene‐based optically transparent electrodes (G‐OTEs; see image) with high conductivity, optical transparency, and chemical stability are fabricated by deposition of exfoliated graphite oxide onto quartz substrates, followed by thermal reduction. Conductive G‐OTEs with a thickness of 8 nm to 24 nm are suitable for spectroelectrochemical investigations across the full UV and visible range.

Self-assembled supramolecular nanotubes of J-aggregated amphiphilic cyanine dye in aqueous solution are employed as chemically active templates for the photoinitiated formation of silver nanowires with a very small and homogeneous diameter of (6.4 +/- 0.5) nm. Key features of the template are (1) its small and well-defined diameter; (2) its photochemical activity, which allows photoinitiation of the structure formation; and (3) the processability in aqueous solution. The latter includes the potential to remove the template after the reaction, or to functionalize it further, e.g. with optoelectronically active polycations, providing access to quasi one-dimensional hybrid structures with well-defined metallic nanowires as a core.

Long-lived exciton coherences have been recently observed in photosynthetic complexes via ultrafast spectroscopy, opening exciting possibilities for the study and design of coherent exciton transport. Yet, ambiguity in the spectroscopic signals has led to arguments for interpreting them in terms of the exciton dynamics, demanding more stringent tests. We propose a novel strategy, Quantum Process Tomography (QPT) for ultrafast spectroscopy, to reconstruct the evolving quantum state of excitons in double-walled supramolecular light-harvesting nanotubes at room temperature. The protocol calls for eight transient grating experiments with varied pulse spectra. Our analysis reveals unidirectional energy transfer from the outer to the inner wall excitons, absence of nonsecular processes, and an unexpected coherence between those two states lasting about 150 femtoseconds, indicating weak electronic coupling between the walls. Our work constitutes the first experimental QPT in a "warm" and complex system, and provides an elegant scheme to maximize information from ultrafast spectroscopy experiments.Recently, there has been great excitement about the detection of long-lived coherent dynamics in natural lightharvesting photosynthetic complexes via two-dimensional spectroscopy [1][2][3]. This long-lived coherence has generated interest and debate about its role in the efficient design of light-harvesting and exciton transport in biological and artificial settings [4][5][6][7]. These discussions have highlighted the importance of correctly interpreting the spectroscopic signals in terms of the microscopic dynamics in the material. The interplay between excitonic dynamics and vibrational dynamics can produce complex and potentially ambiguous spectroscopic signals, which can make extraction of information about exciton transport challenging [8][9][10]. Therefore, it is essential to develop methods to reliably extract the quantum dynamics of the interrogated material. In this article, we demonstrate the systematic characterization of the quantum dynamics of a condensed phase molecular system, namely, the excitons originating from the inner and outer walls of supramolecular light-harvesting nanotubes, via ultrafast Quantum Process Tomography (QPT) [11][12][13]. This manuscript is organized as follows: First, we briefly sketch the QPT formalism as a general method to maximize information from a quantum system interacting with its environment. Then, we describe the nanotubes and the optical setup, and explain how these two are ideally suited for the QPT protocol. Finally, we present the experimental data and its analysis, yielding a full characterization of the quantum dynamics of the excitonic system. To our knowledge, this article constitutes the first experimental realization of QPT on a molecular system in condensed phase, and provides general guidelines to adapt standard spectroscopic experiments to carry out QPT.The time evolution of the excited state of an open quantum system (a system interacting with its environme...

Polymer particles are promising particulate materials for renowned biomedical applications such as targeted drug delivery, tissue engineering and biosensing. Surface properties of the polymer particles are of key importance for biomedical applications because they directly interact with biological systems. Particularly, wrinkled as well as porous surfaces possess an enhanced ability for cell attachment without any additional chemical modification. Therefore, a key objective is to fabricate the particles with desired degree of wrinkles and porosity.Many methods such as solvent evaporation, plasma treatment, emulsion instability, and electro-spraying are being employed for the generation of porous, wrinkled and/or textured surfaces. Advantageously, an application of microfluidics can support the induction of surface instabilities on droplets in a case of droplet-based systems. Furthermore, microfluidics allows tuning of size and shape of the generated droplets as well as particles with desired surface textures. In this mini-review article, surface characteristics (especially surface wrinkles and porosity) of the hydrophobic and hydrophilic polymer particles are presented for the potential applications toward biological as well as biomedical field. In addition, the impact of microfluidics is highlighted in order to produce the polymer particles of functional surface properties.