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

ton. To collect the remaning sufonics ~ndividually, we then renlected the sufoncs n t o the C , which was equpped ~511th a 10 m by 100 lnln Phenomenex (Torrance. CA) star-ion anon exchange column, and eluted them twth a 5.4 m M Na,CO, + 5.1 mM NaHCO, buffer, l?le separated ESA f r o~n a small amount o4 co-eutng sulfate by reinjecting the ti~!o compounds and eluting them with a 3.2 m M Na,CO, + 3 1 NaHCO, m M buffer. Basene separation between MSA and ESNsulfate vias -2 min; betvieen ESA. sulfate and i?SA, t vias -9 min, and between ESA and sulfate, it vias -1 min. Ater re-~noval of the carbonate buffer with HCI, each compound twas then placed n a quanz tube and dred by rotary evaporation (maxmu~n temperature -50'C).Copper oxde was then placed :n each tube, and h:gh vacuum, with m~lo warmin9 (<10S3C), was used for co~npete drying. The sa~nples v/ere then sealed and combusted to sulfate, CO,, an0 H, O at 500'C. The CO, and H 2 0 were collected w~t h a proced~re smiar to that of Epsten et a1 (73). The H, O vias con\!ened to H by the method of Cole~nan and Moore (27) viith a znc catalyze f r o~n J. M. Hayes of Indiana Unversit),. The CO, and H were then analyzed w~t h 6-60-Nuclide and 3-60-HD-Nuclide mass spectrometers. The sulfate vias extracted from each tube with hydrochorc acid an0 prepared for S isotopic analysis as in (6).

Single-molecule spectroscopy was used to follow the orientation of a single probe molecule in a polymer film in real time. Broad spatially heterogeneous dynamics were observed on long time scales, which result from simple diffusive rotational motions on short time scales. This diffusive behavior persists for many rotations before the molecule's local environment changes to one characterized by a new time scale. This environmental exchange occurs instantaneously on the time scale of the experiment and may arise from large-scale collective motions. The distribution of exchange times for these environments was measured for several temperatures near the glass transition.

Applications of conjugated polymers (CP) in organic electronic devices such as light-emitting diodes and solar cells depend critically on the nature of electronic energy transport in these materials. Single-molecule spectroscopy has revealed their fundamental properties with molecular detail, and recent reports suggest that energy transport in single CP chains can extend over extraordinarily long distances of up to 75 nm. An important question arises as to whether these characteristics are sustained when CP chains agglomerate into a neat solid. Here, we demonstrate that the electronic energy transport in aggregates composed of tens of polymer chains takes place on a similar distance scale as that in single chains. A recently developed molecular-level understanding of solvent vapour annealing has allowed us to develop a technique to control the CP agglomeration process. Aggregates with volumes of at least 45,000 nm(3) (molecular weight ≈ 21 MDa) maintain a highly ordered morphology and show pronounced fluorescence blinking behaviour, indicative of substantially long-range energy transport. Our findings provide a new lens through which the ordering of single CP chains and the evolution of their morphological and optoelectronic properties can be observed, which will ultimately enable the rational design of improved CP-based devices.

Single molecule spectroscopy was used to characterize the rotation of fluorescent probe molecules in supercooled o-terphenyl (OTP) just above the glass transition. Rotational motions of spatially isolated individual probe molecules were followed in real time, revealing dynamics that reflect a mosaic of spatially heterogeneous environments. The short-time molecular motions in each environment are found to be diffusional, taking place through a Brownian rotational process characterized by a single rotational correlation time τC. The distribution of rotational diffusion constants for the heterogeneous environments becomes larger as the temperature approaches T g, manifesting increased heterogeneity as OTP is cooled toward the glass transition. After many molecular rotations, the molecule's rotational time changes abruptly. This switch appears instantaneous on the time scale of molecular rotation and is indicative of a rapid rearrangement of the molecule and its local environment. The time required for the environment to change, τEx, is on average 15 times larger than the τC, and nearly 300 times slower than the α-relaxation time in OTP. The ensemble average correlation, 〈τC〉, and exchange times, 〈τEx〉, show a similar temperature dependence, both of which are consistent with the temperature dependence predicted by the Debye Stokes Einstein equation.

All solvents were purchased from Thermo Fisher Scientific Inc. and used without further purification unless otherwise noted. All other chemicals were purchased from Sigma Aldrich Co., Alfa Aesar, or Thermo Fisher Scientific Inc., and were used as received. THF was dried over 3 Å molecular sieves and deoxygenated using a Vacuum Atmospheres Company solvent purification system. 2,5-Dibromo-3-hexylthiophene was prepared according to literature procedures. 1 All manipulations were performed under nitrogen using standard Schlenk techniques. 1 H NMR spectra were recorded using a Varian 400 or 500 MHz spectrometer. Chemical shifts are reported in delta (δ) units and expressed in parts per million (ppm) downfield from tetramethylsilane using the residual non-deuterated solvent as an internal standard. For 1 H NMR: CDCl 3 , 7.24 ppm. Gel permeation chromatography (GPC) was performed at 40°C on a GPCmax VE-2001 (Viscotek) equipped with solvent and sample delivery module, and three fluorinated polystyrene columns (IMBHW-3078 and I-MBMMW-3078 and

The effect of finite trajectory length on single molecule rotational correlation functions has been studied by utilizing time series analysis and numerical simulations. Correlation functions obtained from the trajectories of length less than 100 times the correlation time constant (tau([script-l])) exhibit significant deviations from the true correlation function. The distributions of sample time constants (tau(F)) and stretching exponents (Beta(F)) are mapped by fitting a large number of rotational trajectories to stretched exponentials. As the trajectory length gets smaller, the distributions become broader and asymmetric and their mean values deviate from the true value predicted by pure rotational diffusion. Analysis based on higher order spherical harmonics is suggested as a method for minimizing the effect of the trajectory length. The distributions of time constants for different higher order spherical harmonics are also compared. While the focus of the paper is on rotational correlation functions, the general conclusions apply to any dynamical process that yields an exponentially decaying correlation function.