Observation of Vibronic-Coupling-Mediated Energy Transfer in Light

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Spectroscopy and Photochemistry; General Theory

Observation of Vibronic Coupling Mediated Energy Transfer in Light-Harvesting Nanotubes Stabilized in a Solid-State Matrix Raj Pandya, Richard Chen, Alexandre Cheminal, Tudor H Thomas, Arya Thampi, Arelo Tanoh, Johannes M. Richter, Ravichandran Shivanna, Felix Deschler, Christoph Schnedermann, and Akshay Rao J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.8b02325 • Publication Date (Web): 27 Aug 2018 Downloaded from http://pubs.acs.org on September 1, 2018

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The Journal of Physical Chemistry Letters

Observation of Vibronic Coupling Mediated Energy Transfer in Light-Harvesting Nanotubes Stabilized in a Solid-State Matrix 1

Raj Pandya, 1Richard Chen, 1Alexandre Cheminal, 1Tudor Thomas, 1Arya Thampi, 1Arelo

Tanoh,

1

Johannes

Richter,

1

Ravichandran

Shivanna,

1

Felix

Deschler,

2

Christoph

Schnedermann and 1Akshay Rao* 1

Cavendish Laboratory, University of Cambridge, J.J. Thompson Avenue, CB3 0HE,

Cambridge, United Kingdom 2

Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street,

Cambridge, Massachusetts 02138, USA

Abstract Ultrafast vibrational spectroscopy is employed to obtain real-time structural information of energy transport in double-walled light harvesting nanotubes at room temperature, stabilized in a host matrix to mimic the rigid scaffolds of natural light harvesting systems. We observe evidence of a low-frequency vibrational mode at 315 cm-1 which transfers excitons from the outer wall of the nanotubes to a crossing point through which energy transfer to the inner wall can occur. This mode is furthermore absent in solution phase. Importantly, the coherence of this mode is not transferred to the inner wall upon energy transfer and is only present on the outer wall’s excited state energy surface, highlighting that complete energy transfer between the outer and inner walls does not take place. Isolation of the individual walls of the nanotubes provides evidence that this mode corresponds to a supramolecular motion of the nanotubes. Our results emphasize the importance of the solid state environment in modulating vibronic coupling and directing energy transfer in molecular light-harvesting systems.

1 ACS Paragon Plus Environment

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Introduction Understanding the mechanisms underlying photosynthesis and replicating it within synthetic systems has been a long-standing goal of modern science. At the heart of photosynthesis is the highly efficient harvesting and rapid transport of photons by antenna structures (chlorosomes) to chemical reaction centres1,2. One important model system that has been designed to mimic chlorosomes are tubular J-aggregates formed from the self-assembly of the

ambiphilic

cyanine

dye,

3,3′-bis(2-sulfopropyl)-

5,5′,6,6′-tetrachloro-1,1′-

dioctylbenzimidacarbocyanine, henceforth referred to as C8S33,4. These have garnered widespread interest due to their structural and chemical similarity to chlorosomes in green sulphur bacteria which are able to carry out photosynthesis in extremely low light conditions5,6.

A wealth of studies has been carried out to elucidate both the structure and photophysics of these light harvesting mimics7–11. Cryogenic-TEM experiments have revealed that the dye molecules self-assemble into nanotubes consisting of two closely spaced walls, the diameter of which can be altered by minor modifications to the cyanine backbone12. In addition, the dye molecules display a herringbone structure and are typically highly uniformly arranged as revealed by near-field optical scanning microscopy13. In solution, the inner and outer wall of the nanotubes are weakly and possibly coherently coupled, as revealed by 2D electronic spectroscopy and transient grating experiments10,11,14. Upon photoexcitation, rapid energy transfer occurs from the outer to the inner wall of the nanotubes on a timescale of 100 – 300 fs15,16. Furthermore, it has been suggested that excitons can diffuse up to 1.6 µm along the nanotubes17,18.


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Despite its importance, little is known about the correlation of the excitonic dynamics with the underlying structural motions within the aggregates occurring after photoexcitation19. Furthermore, photophysical measurements are typically carried out in solutions (under flow) or at cryogenic temperatures as opposed to in the solid state at room temperature20,21. The latter is of particular importance in natural light harvesting systems, since chlorosomes are typically packed tightly together within a rigid scaffold5,22,23. Consequently, to understand the exciton dynamics in bacterial or plant-based systems it is key to study corresponding mimics in the solid state. This point is furthermore heightened for the prospect of utilizing their potential in solid state devices, e.g. photovoltaic cells24, light emitting diodes25 or excitonic circuits26,27.

Here, we employ ultrafast vibrational spectroscopy to develop a real-time structural picture of the photoexcited exciton dynamics in C8S3 nanotubes in both solution and solid states. With the aid of chemical modification techniques we are further able to separate and study the involved transitions of the individual walls. In the solid state, our experiments reveal that energy transfer between the outer and the inner wall of the nanotubes is mediated by a low frequency ‘tuning’ mode at ~315 cm-1. Intriguingly, this mode is only coupled to the excitedstate potential energy surface of the outer wall and does not appear on the inner wall. Combined with the narrow linewidth of this vibrational mode (~20 cm-1), we infer that total population transfer between outer and inner walls does not occur ballistically, but rather incoherently. In solution this vibrational coupling is not observed and instead the spectrum is dominated by vibrational modes of the individual cyanine molecule coupled to the electronic ground state. Our measurements demonstrate how vibrational coherences can be used as a tool to track the efficiency of energy transfer in soft supramolecular systems. The experiments also highlight how, in the solid state, vibronic coupling might be used to tune the nature of energy transfer. More generally they raise questions, both experimental and theoretical, for considering the role of the environment in energy transfer in light-harvesting systems.

Results and Discussion

Figure 1a shows a cartoon representation of the studied J-aggregate nanotubes formed from C8S3. The nanotubes consist of an inner and outer wall with diameters of ~6 and ~13 nm, respectively, and can grow up to tens of microns in length28. Extensive experimental and



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theoretical work has shown that the ambiphilic cyanine dye molecules (inset) pack in a herringbone arrangement on the nanotube (although the precise arrangement is still debated29)

surface,

with

the

hydrophobic

alkyl

chains

buried

inwards

30

and hydrophilic acid groups facing outwards . Based on previous work by Caram et al., we prepared photochemically stable films of J-aggregates in a glassy sugar matrix (Fig 1b, see Methods), which prevents photo-chemical oxidative degradation18,31. Further photostability, against both continuous wave and pulsed radiation, was achieved by preparing the samples in an inert N2 atmosphere with argon-enriched solvents (Supporting Information Figure S1). To provide an internal control sample, we also chemically oxidized the outer wall of the nanotubes (see Methods) prior to embedding the nanotubes into the matrix. This chemical oxidation allows us to effectively “turn off” the absorption due to the outer wall and selectively study the inner wall with transient spectroscopies32 (SI, Figure S2).

Figure 1: Steady-state optical and structural characterization of double-walled nanotubes. (a) Transmission electron micrograph (TEM) image of double-walled nanotubes embedded within a crystalline sugar matrix and schematic of double-walled nanotubes consisting of an inner and outer wall with diameters of ~6 and ~13 nm respectively. The ambiphilic cyanine monomers arrange in a herringbone pattern (pale blue bricks) to form a tubular structure with two cyanine molecules per unit cell. (b) Steady-state absorption spectrum of double-walled nanotubes (black) embedded within a sugar matrix. The inner ‘1’ and outer ‘2’ wall transitions are marked. The transitions ‘3 – 5’ belong to the inner wall and result from two molecules per unit cell. The origin of the low-energy shoulder marked ‘6’ is unclear, but this transition only becomes prominent at cryogenic temperatures. The red curve shows the steady-state absorption spectrum for single-walled nanotubes embedded in a sugar matrix. (c) Energy diagram of double-walled C8S3 nanotubes. Transitions are allowed between the ground state | and the one-exciton states of the outer (| or inner wall (|. In addition, excitedstate absorption can occur between the one-exciton and two-exciton manifolds. In the latter case, two excitons may reside either on the inner wall (|, outer wall (| or one on each (|. The dashed lines indicate transitions resulting from two cyanine molecules per unit cell on the inner wall. The numbers marked correspond to the transitions indicated in the adjacent absorption spectrum.


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The absorption spectrum for a matrix-stabilized film of double-walled nanotubes is shown in Figure 1b (black curve). The peaks labelled ‘1’ and ‘2’ correspond to the one-exciton transitions of the inner and outer wall, respectively. In the spectral region 550 – 580 nm an additional three peaks are resolved. The band ‘3’ has been assigned to overlapping transitions from the two cylinders17,33. The origin of the high-energy transitions ‘4’ and ‘5’ are still unknown, but likely consists of several closely spaced bands. It has been postulated these high energy states exist as a result of having two molecules per unit cell on the inner wall30. Measuring the absorption spectrum at cryogenic temperatures (SI, Figure S3a) reveals a hitherto unknown transition red-shifted from the outer wall exciton peak at ~ 610 nm labelled as ‘6’. This transition appears as a shoulder to the inner wall absorption band and, like band ‘3’, may be a result of overlap between the two nanotube walls. Most likely however this peak arises from some bundling of nanotubes17,28, which are present in dilute quantities in the samples; full assignment is beyond the scope of this work. As noted by Caram et al. lowtemperature photoluminescence measurements (SI, Figure S3b) show that matrix-stabilized nanotubes possess less inhomogeneous broadening than those in solution18. This is likely because in the solid-state nanotubes relax into an optimal arrangement before becoming immobilized in the sugar matrix, whereas in solution random tumbling means that the nanotubes will be in a range of energetic configurations. Figure 1b additionally shows the absorption spectrum of chemically oxidized, ‘single-walled’, C8S3 nanotubes embedded within a sugar matrix (red line). The outer wall absorption at 589 nm is clearly suppressed, with a single peak associated with the inner wall exciton remaining. The broad tail of transitions between 550 – 585 nm also remain on chemical oxidation emphasizing that these transitions (summarized in Figure 1c) are most likely associated with the inner wall30.

To study the role of vibronic coupling in transferring energy between the outer and inner wall, femtosecond transient absorption (fs-TA) measurements were performed. Films of matrix-stabilized aggregates with single and double walls were excited with a ~12 fs pulse (verified by SHG-FROG and reference solvent; SI, Figure S4) tuned to overlap with both the inner and outer wall excitonic transitions (λex = 595 nm, FWHM ~50 nm). The pump fluence of ~19 µJ/cm2 resides at the threshold of the linear excitation regime but we confirmed that no significant contribution to the dynamics from exciton – exciton annihilation affected the measured signals (SI, Figure S5). In addition, we recorded the absorption after each sweep to ensure minimal degradation had occurred.



Figure 2a shows the transient absorption map for a double-walled nanotube film, where ∆T/T is plotted as functions of probe wavelength and time delay between pump and probe pulses. ∆T is the change in probe transmission of the sample with/without the pump pulse, and T is the probe transmission without the pump pulse. The positive features observed for the double-walled nanotube film (Figure 2a) centered at 589 nm and 599 nm correspond to an overlap of the bleach of the ground state – one-exciton transition (GSB) and stimulated emission (SE) for the outer and inner wall, respectively. The negative photo-induced absorption (PIA) features at 582 nm and 592 nm correspond to optical transitions from the one to two – exciton manifolds of the outer and inner walls. Following the initial rise, the inner wall GSB feature continues to grow until ~380 fs on a similar timescale as the decay of the outer wall GSB. This is in line with ultrafast photoluminescence measurements (SI, Figure S6) and previous reports of energy transfer between the two walls on the timescale of ~300 fs34. In addition, polarization-resolved measurements on flow-aligned nanotubes (SI, Figure S7) reveal a slow (~5 ps) rise in the GSB bleach of the higher energy bands of the inner wall. This suggests that energy transfer can still occur on a slower timescale greater than the initial 300 fs. Furthermore, higher energy transitions of the inner wall, associated with bands 3-5 in Figure 1c, can be resolved.


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Figure 2: Ultrafast vibronic dynamics and time-domain impulsive vibrational Raman spectra of matrix-stabilized double-walled C8S3 nanotubes. (a) TA map of double-walled nanotubes following photoexcitation with a ~12 fs pulse covering both the inner (IW) and outer wall (OW) absorption peaks at ~589 and 599 nm. The positive features centered at ~587 and ~598 nm are an overlap between the ground state bleach (GSB) and stimulated emission (SE) of the outer and inner walls respectively. The negative features centered at ~582 nm and ~592 nm correspond to excited state transitions between S1 and Sn of the OW and IW. Selected transient absorption spectra (top) at 50, 350, 1000 and 10000 fs illustrate the rapid initial dynamics. Whilst the population of the outer wall rapidly drops (blue arrow) the inner wall population clearly grows within the first 350 fs. (b) Wavelength-resolved Fourier-transform power spectra of C8S3 double-walled nanotubes stabilized in a sugar matrix. The impulsive Raman spectra along the outer wall PIA and inner wall GSB are given by the green and blue spectra respectively. Spectra are normalized to the maximum peak strength. In this former case, vibrational coherences are present in both the ground (GS) and excited stated (ES). The non-resonant spectrum (grey) is produced in a separate experiment (λex = 740 nm) where vibrational coherences are generated only in the ground state and there is no electronic decay. For the off-resonant measurements the FFT power spectrum is averaged over probe wavelengths 580-620 nm.

Superimposed on the electronic population dynamics shown in the TA map in Figure 2a we observe strong oscillatory modulations arising from impulsively excited wave packets produced by the ultrashort pump pulse. The vibrational wave packets can be associated with either the ground state or the excited state potential energy surface35,36. Fourier transforming these oscillatory components into the frequency domain (SI, Figure S8-S10) and examining spectra recorded at specific probe wavelengths allows us to infer the specific vibrational modes that couple to a given transition, as shown in Figure 2b. The GSB/SE region of the inner wall at 600 nm (blue curve in Figure 2b) is dominated by weak vibrational modes in the frequency range 1000 – 1500 cm-1 37. Theoretical calculations for similar cyanine aggregates have assigned modes in this region to stretching and breathing modes of the benzene and imidazole rings38. The grey spectrum in Figure 2b (off-resonant excitation with pulse centered at 740 nm, FWHM ~50 nm, ~14 fs) show these modes exclusively couple to the ground state energy surface. For the outer wall, however, a single strong mode centered at 315 cm-1 (FWHM ~20 cm-1) is observed (bottom panel in Figure 2b), which is present only in the resonant excitation spectrum. Plotting the mode intensity as a function of wavelength (SI, Figure S11) shows that this mode most strongly modulates the GSB/PIA of the outer wall (585 nm). Upon tuning the pump pulse energy, this mode is observed only when the outer wall is excited. Overlapping the pump pulse with the inner wall excitonic transition at 600nm does not produce the 315



cm-1 mode in the TA data. In addition, the mode is not observed in off-resonant steady-state Raman measurements. Resonance Raman experiments could not be carried out due to the high powers required and hence large-scale sample degradation along with background fluorescence. Consequently we conclude that its presence in the PIA of the inner wall is likely due to the strongly overlapped features, and that this mode is purely coupled to the excited state potential energy surface of the outer wall.

Figure 3: Ultrafast vibronic dynamics and time-domain impulsive vibrational Raman spectra of matrix-stabilized single-walled C8S3 nanotubes. (a) TA map of single-walled nanotubes following photoexcitation with the same pulse as used to excite double-walled nanotubes. GSB and PIA features observed at 597 nm and 594 nm are associated solely with the inner wall. Any remaining absorption from the oxidized OW is either too weak to be detected or masked by the inner wall PIA. The spectral slices (top) show the GSB/PIA of the IW are slightly red shifted compared to in the double-walled case; they decay more rapidly as expected. (b) Wavelength-resolved Fourier-transform power spectra of ‘single-walled’ C8S3 nanotubes stabilized in a sugar matrix. The green and blue spectra indicate GS and ES vibrational coherences that influence the inner wall PIA and inner wall GSB respectively. The spectra are dominated by GS modes in the 250 – 480 cm-1 region as well as the aforementioned modes of the cyanine monomer. No mode is observed at 315 cm-1. Modes influencing the ES are observed at ~725 cm-1 and ~940 cm-1. The mode at ~665 cm-1 results from the sugar matrix.

Exciton dynamics of chemically-oxidized nanotubes


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To further track the origin of the low-frequency excited-state mode at 315 cm-1, we carried out vibrational spectroscopy, under the same experimental conditions, on nanotubes where the outer wall has been chemically oxidized30,33. The TA spectrum (Figure 3a) contains GSB/SE and PIA bands associated purely with the transitions of the inner wall. The GSB/SE at 599 nm shows a monotonic decay after an initial rise, since energy is no longer being transferred from the high energy outer wall to the inner wall. In the case of the PIA, the decongestion of the spectrum following chemical oxidation allows this band to be clearly resolved, with its average lifetime increased to ~630 fs compared to the double-walled case of ~180 fs. This is surprising at first but can be explained by the fact that the same PIA feature in the double-walled TA spectrum is overlapped with the outer wall GSB, therefore giving a misleadingly short PIA lifetime. A more quantitative evaluation of these lifetimes is challenging because of the strongly overlapping features in these spectra that are difficult to separate using spectral decomposition algorithms.

In Figure 3b we show the vibrational spectrum at various probe wavelengths for the singlewalled tubes in films. One striking difference to that of the double-walled nanotubes is the significant increase in the number of vibrational modes. In the high-frequency 1000 – 1500 cm-1 region, these are similar to the double-walled sample as would be expected for these ground-state modes. In the 200 – 800 cm-1 region, however, we observe a significantly larger number of modes most of which are coupled to the ground-state potential energy surface, except those at around 720, 940 and 1030 cm-1, which are coupled to the excited state. Importantly, the mode at 315 cm-1 is not observed, confirming that it is not a mode of the inner wall. We observe a similar phenomenon in solution, where the number of modes is again greater, particularly for the single-walled nanotubes (SI, Figure S10 and S11). Furthermore, for both double- and single-walled nanotubes the oscillation at 315 cm-1 is not found in solution phase. Care must be taken to directly compare these two cases. In films the nanotubes possess significantly less inhomogeneous broadening than in solution as shown by the reduced spectral shift and narrowing in absorption peaks on cooling to cryogenic temperatures. This difference in disorder is likely of structural origin hampering a direct comparison.

Structural origin of vibronic coupling



The vibrational mode at 315 cm-1 (i.e. 39 meV) is approximately equal to the energy difference between the inner and outer walls of the nanotube (37 meV). Hence, on first appearance the presence of oscillations modulating the TA spectrum at such a frequency suggest an electronic coherence between the two walls. However, the mode only modulates the outer wall transitions, implying that the observed mode does not modulate the population between the two walls, as would be expected for such an electronic coherence39–41. We remark that no such electronic coherences have been observed in 2D electronic spectroscopy experiments that are usually used to identify such behavior10,16. In the work of Zhou-Cohen et

al., quantum process tomography experiments were used to observe a weak electronic beating signature between nanotube walls in solution11. This suggests that to detect any electronic coherence, more sensitive higher-order non-linear spectroscopy is required. Since both nanotubes are made of the same cyanine molecule our observations suggest that this low-frequency mode is not related to a vibrational mode of the C8S3 monomer, but to a ‘supramolecular motion’ of several molecules within the entire outer wall aggregate structure. Indeed no mode is observed at 315 cm-1 in the Raman spectrum of C8S3 monomers (SI, Figure S15). Furthermore, this mode is only observed in the solid state, suggesting interactions with the sugar matrix help stabilize the mode and allow coherent vibronic couplings to be observed. We do remark that the oxidation of the double-walled nanotubes may lead to some partial oxidation and damaging of the inner wall dye molecules; this factor cannot be ruled out in potential destruction of the 315 cm-1 mode in single-walled nanotubes.

Influence of vibronic coupling on exciton dynamics The linewidth of a mode obtained on Fourier transforming of the TA spectrum is inversely proportional to the lifetime of the transition it is associated with. For example, in β-Carotene, vibronic bands associated with the S2 are typically ~300 cm-1 broad because the state only lives for 200 fs42. Conversely in the case of CdSe nanocrystals the modes associated with exciton-LO phonon coupling have typically narrow linewidths resulting, in part, from the nanosecond excited state lifetime43,44. A direct comparison between experiments is impossible because this width is also affected to some extent by pulse duration, Fourier windowing function etc., but the 20 cm-1 FWHM for the mode at 315 cm-1 indicates it is associated with a relatively long-lived state. Fitting the dephasing time of the mode at 315 cm-1 (SI, Figure S8) gives a value of ~290 fs in line with the time for outer to inner wall energy transfer. More specifically this implies that the vibrational coherence is long-lived and not destroyed on the outer wall by the energy transfer event. We can hence assign this mode


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as being a ‘tuning’ mode with a large Franck-Condon factor, i.e. with a large displacement of energy surface along that mode45,46. The proximity of this mode's energy to the energetic separation between the two walls may be pure coincidence. However, it more likely suggests

that the mode is somehow related to bringing the system to a crossing of the potential energy surfaces, through which energy transfer occurs. In the case of ballistic or ultrafast transfer between the two walls, all energy would be deposited onto the inner tube resulting in fast dephasing of the coherence on the outer wall (on the excited state) and conversely resulting in a broad linewidth, contrary to our observations (Figure 2b). The small energy gap between walls (~200 cm-1) compared to kbT (~300 cm-1) means that even in the case of ballistic transfer we would expect, as observed, emission from both the outer and inner walls in photoluminescence measurements (time-resolved and steady-state; SI, Figure S6). The proximity of this mode's energy to the energetic separation between the two walls hence provides additional support for the assignment to a tuning mode. As such, following photoexcitation this tuning mode can quickly close the energy mismatch between the outer and inner walls, allowing for efficient energy transfer. It should be noted that there are likely additional processes (e.g. thermalization between states) contributing to the dephasing of the mode at 315 cm-1, however these are too fast to be resolved in our experiments (further discussion see SI, Figure S8). For nanotubes embedded within a sugar matrix the outer to inner wall transfer time (judged from the rise of the inner wall ground state bleach; SI, Figure S12) is faster 277 ± 19 fs (film) compared to 319 ± 13 fs (solution). Hence it can be suggested that the vibrational mode at 315 cm-1 also potentially plays a role in enhancing the speed of energy transfer.

Conclusion Taken together, we have demonstrated that the energy transfer between the outer and inner walls of C8S3 nanotubes is mediated by a single low-frequency vibrational ‘tuning’ mode, observable only when the nanotubes are stabilized in a rigid sugar matrix. The exact molecular nature of this mode is unknown but is likely related to the supramolecular structure of the aggregates, specifically set up along the diameter of the nanotubes. Significantly, our results suggest that by tuning vibrational modes, the nature of energy transfer in these and similar light-harvesting mimics can be altered and potentially finely controlled. In chemical terms this might be achieved by swapping the chlorine groups on the benzene ring of the monomers for other halogens to reduce the tube diameter12 or through careful balancing of



the solvent ratios to cause tubes to bundle together47. Our experiments in the solid state render the results obtained here directly applicable to nanoscale devices and natural harvesting complexes, which in nature are surrounded by a rigid protein matrix48,49. This surrounding solid state environment can modulate the vibronic coupling, which in turn controls the energy transfer dynamics of these systems.

Experimental Methods

Sample preparation Solutions of double-walled nanotubes were prepared using a method extensively detailed in the literature10,17,18,30,33. Briefly, a solution of 3 mM C8S3 monomer (FEW chemicals) was prepared in methanol. This was added in a ~1:4 ratio with deionized water and stored in the dark for 24 – 48 h. All solvents were degassed via a freeze-pump-thaw sequence or by holding under low pressure and subsequently bubbling with Ar gas. Preparation was carried out in an inert N2 atmosphere. The double-walled nanotubes were then mixed in a 1:1 ratio with a saturated solution of 50% sucrose (Sigma) and 50% trehalose (Alfa Caesar) as detailed by Caram et al.18; this solution was also degassed before mixing with nanotubes to minimize oxidative degradation. Samples were then drop-flowed or drop casted and spread onto precleaned (sonication in acetone and isopropanol followed by oxygen plasma) quartz substrates (0.15 mm thickness) and then allowed to dry in an N2 atmosphere under a vacuum of ~0.3 atm for 24 - 48 h. Subsequently, they were encapsulated by placing a second larger coverslip (with spacer) atop of the sample and then sealing with epoxy glue. For the preparation of single-walled nanotubes, 10 mM AgNO3 solution was added in a 1:40 ratio to a solution of double-walled nanotubes30,50. An absorption spectrum was taken every 10 minutes to monitor the oxidation, typically after 100 min the outer wall was fully oxidized. Residual AgNO3 was removed by precipitation with NaCl32. The preparation of films followed the same procedure as for the double-walled nanotubes with embedding in a sugar matrix.

Temperature-Dependent Absorption Spectroscopy Linear absorption spectra of nanotube solutions, placed in a 0.2 mm path length cuvette (Starna), were measured using commercial Perkin-Elmer lambda 750 UV-VIS-NIR set-up. A


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Xe-lamp was used as the light source and all measurements were performed under standard ambient conditions. The spectra were measured simultaneously with the solvent to correct for its absorbance.

Temperature-dependent absorption measurements (double-walled films only) were carried out using an Agilent Cary 6000i UV–VIS–NIR spectrophotometer with blank substrate correction. Samples were placed in a continuous-flow cryostat (Oxford Instruments Optistat CF-V) under helium atmosphere. We allowed the sample temperature to equilibrate for 30 minutes before taking data.

Temperature-Dependent Photoluminescence Spectroscopy Films of matrix-stabilized aggregates were deposited onto Spectrosil glass and transferred from a N2 glove box to a continuous-flow cryostat (Oxford Instruments Optistat V) under helium atmosphere. PL was measured under an excitation power of ~4 W/cm2 at an excitation wavelength of 405 nm. We allowed the sample temperature to equilibrate for 30 min before taking data. Emission was measured using an Andor iDus DU420A Si detector.

Femtosecond Transient Absorption Spectroscopy The fs-TA experiments were performed using an Yb-based amplified system (PHAROS, Light Conversion) providing 14.5 W at 1030 nm and 10 kHz repetition rate. The probe beam is generated by focusing a portion of the fundamental in a 4 mm YAG substrate and spans from 520 nm to 1400 nm. The pump pulses were generated in home-built noncollinear optical parametric amplifiers (NOPAs) as outlined previously by Liebel et al.51. The NOPAs output (~4-5 mW) was centered either between 550 nm and 620 nm or at 740 nm and pulses were compressed using a chirped mirror and wedge prism (Layterc) combination to a temporal duration of 12 fs and 14 fs, respectively, as determined by second harmonic generation frequency resolved optical gating (SHG-FROG)52. The probe white light is delayed using a computer-controlled piezoelectric translation stage (Physik Instrumente), and a sequence of probe pulses with and without pump is generated using a chopper wheel (Thorlabs) on the pump beam. The pump irradiance was set to 19 µJ/cm2. After the sample, the probe pulse was split with a 950 nm dichroic mirror (Thorlabs). The visible part (520 – 950 nm) is then imaged with a Silicon photodiode array camera (Entwicklunsbüro Stresing; visible monochromator 550 nm blazed grating). Measurements were carried out with a time step size of 6 fs out to 1.5 ps, in order to minimize exposure time of the sample to the beam.



Unless otherwise stated all measurements were carried out with the probe polarization set at ‘magic angle’ (54.7°) with respect to that of the pump to avoid photoselection effects53. For polarization-resolved spectroscopy (solutions only), nanotube solutions were continuously flowed through a 0.1 mm path length flow cell (Starna: 48/UTWA2/Q/0.1). The pump and probe pulses were then adjusted by means of a half-waveplate (Eksma) such that their polarization could be set either parallel or perpendicular to that of the alignment of nanotubes.

Steady-State Raman Spectroscopy Off-resonance Raman spectra of the samples were measured using a confocal microscope coupled to the Horiba T64000 Raman system, equipped with an achromatic water immersion objective with 100x magnification and 1.2 numerical aperture. A continuous-wave diode laser of 785 nm wavelength (Toptica Photonics Xtra 785 nm) was used as the excitation source. Spectra were acquired on a liquid-N2 cooled CCD detector after dispersing the Raman signal through a 800 mm focal length spectrometer equipped with a 600 lines/mm grating. To maximize the collected signal, the confocal pinhole was set to 300 µm and for optimal spectral resolution, the slit width was set to 200 µm. Each spectrum was recorded with an exposure time of 30 s and averaged over 4 cycles.

Transient Photoluminescence Spectroscopy Ultrafast photoluminescence (PL) spectroscopy was carried out using the transient grating technique developed by Chen et al.54. Briefly, a Ti:Sapphire amplifier system (SpectraPhysics Solstice Ace) operating at 1 kHz generating 80-fs 800 nm pulses is split into the pump and gate beam arms. The pump beam (400 nm) was generated by second harmonic generation in a BBO crystal and focused onto the sample. The gate beams are focused onto the gate medium (fused silica), crossing at an angle of ∼5° and overlapping with the focused PL. The two gate beams interfere and create a transient grating in the gate medium due to a modulation of the refractive index via the optical Kerr effect. Temporal overlap between the two gate beams is achieved via a manual delay stage. The PL is then deflected on the transient grating, causing a spatial separation of the gated signal from the PL background. The gated signal is focused onto a spectrometer entrance (Princeton Instruments SP 2150)


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after long- and short-pass filters to remove scattered pump and gate light, respectively. Gated PL spectra are measured using an intensified CCD camera (Princeton Instruments, PIMAX4).

Confocal Photoluminescence Microscopy PL microscopic images were taken using a WITec alpha 300 RAS confocal microscope. A fiber-coupled 405nm CW laser (Coherent LaserCUBE) was used to excite the sample (Excitation power = 0.5 µW). The sample was rested on an X-Y piezo-scanning stage. The laser was focused using 100x (Nikon lens, NA = 0.9) objective with an effective excitation beam diameter of ~0.5 µm. The PL was collected in reflection mode from the same 100x objective. A 435nm long pass filter was used in the detection line to block the excitation component of reflected laser (405nm). The PL spectrum was acquired using a spectrometer fitted with a CCD array detector (Andor IDus). The movement of stage and acquisition of PL spectrum was controlled by WITecScanCtr Plus spectroscopy software. All the data were analyzed and plotted with the WITecProject FOUR software.

Transmission Electron Microscopy (TEM) Approximately 10 µl of dilute nanotube/sugar matrix solution was drop casted onto a TEM copper grid with a Holey carbon support film in an inert atmosphere from dilute solution. Once dried bright field TEM was carried out in a FEI Tecnai Osiris TEM operated at 200 kV.

Data Analysis Data analysis was carried out with custom codes written using MATLAB and Origin software. The details of specific algorithms used in the analysis are discussed in the Supporting Information.

Acknowledgments R.P thanks F. Auras and J. Gorman (Cambridge) for assistance and advice with preparation of C8S3 nanotube films and Q. Gu for assistance with pulse compression. The authors thank the EPSRC and Winton Program for Physics of Sustainability for financial support.



Supporting Information Summary Sample characterization and photochemical stability analysis, cryogenic absorption and photoluminescence, transient photoluminescence spectroscopy, pump energy, polarization and bandwidth dependent fs-transient absorption spectroscopy, extraction of vibrational modes.

References (1)

Moroney, J. V; Ynalvez, R. A. Algal Photosynthesis. In Encyclopedia of Life Sciences; 2009.

(2)

Bowyer, J. R.; Leegood, R. C. Photosynthesis. In Plant Biochemistry; 1997; pp 49– 110.

(3)

Pawlik, A.; Ouart, A.; Kirstein, S.; Abraham, H.-W.; Daehne, S. Synthesis and UV/Vis Spectra of J-Aggregating 5,5′,6,6′-Tetrachlorobenzimidacarbocyanine Dyes for Artificial Light-Harvesting Systems and for Asymmetrical Generation of Supramolecular Helices. European J. Org. Chem. 2003, 2003 (16), 3065–3080.

(4)

De Rossi, U.; Moll, J.; Spieles, M.; Bach, G.; Dähne, S.; Kriwanek, J.; Lisk, M. Control of the J‐Aggregation Phenomenon by Variation of the N‐alkyl‐substituents. J.

für Prakt. Chemie/Chemiker‐Zeitung 1995, 337 (1), 203–208. (5)

Orf, G. S.; Blankenship, R. E. Chlorosome Antenna Complexes from Green Photosynthetic Bacteria. Photosynthesis Research. 2013, pp 315–331.

(6)

Adolphs, J.; Renger, T. How Proteins Trigger Excitation Energy Transfer in the FMO Complex of Green Sulfur Bacteria. Biophys. J. 2006, 91 (8), 2778–2797.

(7)

Qiao, Y.; Polzer, F.; Kirmse, H.; Kirstein, S.; Rabe, J. P. Nanohybrids from Nanotubular J-Aggregates and Transparent Silica Nanoshells. Chem. Commun. 2015,

51 (60), 11980–11982. 16 ACS Paragon Plus Environment

Page 16 of 21

Page 17 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(8)

Qiao, Y.; Polzer, F.; Kirmse, H.; Steeg, E.; Kühn, S.; Friede, S.; Kirstein, S.; Rabe, J. P. Nanotubular J-Aggregates and Quantum Dots Coupled for Efficient Resonance Excitation Energy Transfer. ACS Nano 2015, 9 (2), 1552–1560.

(9)

Doria, S.; Sinclair, T.; Klein, N.; Bennet, D.; Chuang, C.; Freyria, F.; Steiner, C.; Foggi, P.; Nelson, K.; Cao, J.; et al. Photochemical Control of Exciton Superradiance in Light-Harvesting Nanotubes. ACS Nano 2018, 12 (5), 4556–4564.

(10)

Eisele, D. M.; Arias, D. H.; Fu, X.; Bloemsma, E. A.; Steiner, C. P.; Jensen, R. A.; Rebentrost, P.; Eisele, H.; Tokmakoff, A.; Lloyd, S.; et al. Robust Excitons Inhabit Soft Supramolecular Nanotubes. Proc. Natl. Acad. Sci. 2014, 111 (33), E3367–E3375.

(11)

Yuen-Zhou, J.; Arias, D. H.; Eisele, D. M.; Steiner, C. P.; Krich, J. J.; Bawendi, M. G.; Nelson, K. A.; Aspuru-Guzik, A. Coherent Exciton Dynamics in Supramolecular Light-Harvesting Nanotubes Revealed by Ultrafast Quantum Process Tomography.

ACS Nano 2014, 8 (6), 5527–5534. (12)

Kriete, B.; Bondarenko, A. S.; Jumde, V. R.; Franken, L. E.; Minnaard, A. J.; Jansen, T. L. C.; Knoester, J.; Pshenichnikov, M. S. Steering Self-Assembly of Amphiphilic Molecular Nanostructures via Halogen Exchange. J. Phys. Chem. Lett. 2017, 8 (13), 2895–2901.

(13)

Eisele, D. M.; Knoester, J.; Kirstein, S.; Rabe, J. P.; Vanden Bout, D. A. Uniform Exciton Fluorescence from Individual Molecular Nanotubes Immobilized on Solid Substrates. Nat. Nanotechnol. 2009, 4 (10), 658–663.

(14)

Abramavicius, D.; Nemeth, A.; Milota, F.; Sperling, J.; Mukamel, S.; Kauffmann, H. F. Weak Exciton Scattering in Molecular Nanotubes Revealed by Double-Quantum Two-Dimensional Electronic Spectroscopy. Phys. Rev. Lett. 2012, 108 (6).

(15)

Pugžlys, A.; Augulis, R.; Van Loosdrecht, P. H. M.; Didraga, C.; Malyshev, V. A.; Knoester, J. Temperature-Dependent Relaxation of Excitons in Tubular Molecular Aggregates: Fluorescence Decay and Stokes Shift. J. Phys. Chem. B 2006, 110 (41), 20268–20276.

(16)

Sperling, J.; Nemeth, A.; Hauer, J.; Abramavicius, D.; Mukamel, S.; Kauffmann, H. F.; Milota, F. Excitons and Disorder in Molecular Nanotubes: A 2D Electronic Spectroscopy Study and First Comparison to a Microscopic Model. J. Phys. Chem. A

2010, 114 (32), 8179–8189. (17)

Clark, K. A.; Krueger, E. L.; Vanden Bout, D. A. Direct Measurement of Energy Migration in Supramolecular Carbocyanine Dye Nanotubes. J. Phys. Chem. Lett. 2014,

5 (13), 2274–2282. 17 ACS Paragon Plus Environment


(18)

Caram, J. R.; Doria, S.; Eisele, D. M.; Freyria, F. S.; Sinclair, T. S.; Rebentrost, P.; Lloyd, S.; Bawendi, M. G. Room-Temperature Micron-Scale Exciton Migration in a Stabilized Emissive Molecular Aggregate. Nano Lett. 2016, 16 (11), 6808–6815.

(19)

Hasegawa, D.; Nakata, K.; Tokunaga, E.; Okamura, K.; Du, J.; Kobayashi, T. Vibrational Energy Flow between Modes by Dynamic Mode Coupling in THIATS JAggregates. J. Phys. Chem. A 2013, 117 (45), 11441–11448.

(20)

Engel, G. S.; Calhoun, T. R.; Read, E. L.; Ahn, T. K.; Man\v{c}al, T.; Cheng, Y. C.; Blankenship, R. E.; Fleming, G. R. Evidence for Wavelike Energy Transfer through Quantum Coherence in Photosynthetic Systems. Nature 2007, 446 (7137), 782–786.

(21)

Lee, H.; Cheng, Y. C.; Fleming, G. R. Coherence Dynamics in Photosynthesis: Protein Protection of Excitonic Coherence. Science (80-. ). 2007, 316 (5830), 1462–1465.

(22)

Oostergetel, G. T.; van Amerongen, H.; Boekema, E. J. The Chlorosome: A Prototype for Efficient Light Harvesting in Photosynthesis. Photosynthesis Research. 2010, pp 245–255.

(23)

Ganapathy, S.; Oostergetel, G. T.; Wawrzyniak, P. K.; Reus, M.; Gomez Maqueo Chew, A.; Buda, F.; Boekema, E. J.; Bryant, D. A.; Holzwarth, A. R.; de Groot, H. J. M. Alternating Syn-Anti Bacteriochlorophylls Form Concentric Helical Nanotubes in Chlorosomes. Proc. Natl. Acad. Sci. 2009, 106 (21), 8525–8530.

(24)

Abdel-Mottaleb, M. S. A.; Abdel-Mottaleb, M. M. S.; Hafez, H. S.; Saif, M. JAggregates of Amphiphilic Cyanine Dyes for Dye-Sensitized Solar Cells: A Combination between Computational Chemistry and Experimental Device Physics.

Int. J. Photoenergy 2014, 2014, 1–6. (25)

Chang, J.-F.; Chien, F.-C.; Cheng, C.-W.; Lin, C.-C.; Lu, Y.-H.; Wei, H.-S.; Jaing, C.C.; Lee, C.-C. Process Dependence of Morphology and Microstructure of Cyanine Dye J-Aggregate Film: Correlation with Absorption, Photo- and Electroluminescence Properties. Opt. Express 2014, 22 (24), 29388–29397.

(26)

Cui, Q. H.; Peng, Q.; Luo, Y.; Jiang, Y.; Yan, Y.; Wei, C.; Shuai, Z.; Sun, C.; Yao, J.; Zhao, Y. S. Asymmetric Photon Transport in Organic Semiconductor Nanowires through Electrically Controlled Exciton Diffusion. Sci. Adv. 2018, 4 (3).

(27)

Boulais, E.; Sawaya, N. P. D.; Veneziano, R.; Andreoni, A.; Banal, J. L.; Kondo, T.; Mandal, S.; Lin, S.; Schlau-Cohen, G. S.; Woodbury, N. W.; et al. Programmed Coherent Coupling in a Synthetic DNA-Based Excitonic Circuit. Nat. Mater. 2018, 17 (2), 159–166.

(28)

Von Berlepsch, H.; Kirstein, S.; Hania, R.; Pugžlys, A.; Böttcher, C. Modification of


Page 18 of 21

Page 19 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the Nanoscale Structure of the J-Aggregate of a Sulfonate-Substituted Amphiphilic Carbocyanine Dye through Incorporation of Surface-Active Additives. J. Phys. Chem.

B 2007, 111 (7), 1701–1711. (29)

Megow, J.; Röhr, M.; Schmidt am Busch, M.; Renger, T.; Mitrić, R.; Kirstein, S.; Rabe, J.; May, V. Site-Dependence of van Der Waals Interaction Explains Exciton Spectra of Double-Walled Tubular J-Aggregates. Phys. Chem. Chem. Phys. 2015, 17, 6741–6747.

(30)

Eisele, D. M.; Cone, C. W.; Bloemsma, E. A.; Vlaming, S. M.; Van Der Kwaak, C. G. F.; Silbey, R. J.; Bawendi, M. G.; Knoester, J.; Rabe, J. P.; Vanden Bout, D. A. Utilizing Redox-Chemistry to Elucidate the Nature of Exciton Transitions in Supramolecular Dye Nanotubes. Nat. Chem. 2012, 4 (8), 655–662.

(31)

Wright, W. W.; Carlos Baez, J.; Vanderkooi, J. M. Mixed Trehalose/sucrose Glasses Used for Protein Incorporation as Studied by Infrared and Optical Spectroscopy. Anal.

Biochem. 2002, 307 (1), 167–172. (32)

Steeg, E.; Polzer, F.; Kirmse, H.; Qiao, Y.; Rabe, J. P.; Kirstein, S. Nucleation, Growth, and Dissolution of Silver Nanostructures Formed in Nanotubular JAggregates of Amphiphilic Cyanine Dyes. J. Colloid Interface Sci. 2016, 472, 187– 194.

(33)

Clark, K. A.; Cone, C. W.; Vanden Bout, D. A. Quantifying the Polarization of Exciton Transitions in Double-Walled Nanotubular J-Aggregates. J. Phys. Chem. C

2013, 117 (50), 26473–26481. (34)

Augulis, R.; Pugžlys, A.; Van Loosdrecht, P. H. M. Exciton Dynamics in Molecular Aggregates. Phys. Status Solidi 2006, 3 (10), 3400–3403.

(35)

Liebel, M.; Schnedermann, C.; Wende, T.; Kukura, P. Principles and Applications of Broadband Impulsive Vibrational Spectroscopy. J. Phys. Chem. A 2015, 119 (36), 9506–9517.

(36)

Liebel, M.; Kukura, P. Broad-Band Impulsive Vibrational Spectroscopy of Excited Electronic States in the Time Domain. J. Phys. Chem. Lett. 2013, 4 (8), 1358–1364.

(37)

Knoester, J. Modeling the Optical Properties of Excitons in Linear and Tubular JAggregates. International Journal of Photoenergy. 2006.

(38)

Coles, D. M.; Meijer, A. J. H. M.; Tsoi, W. C.; Charlton, M. D. B.; Kim, J.; Lidzey, D. G. A Characterization of the Raman Modes Ina J-Aggregate-Forming Dye: A Comparison between Theory and Experiment. J. Phys. Chem. A 2010, 114, 11920– 11927.



(39)

Rosca, F.; Kumar, A. T. N.; Ye, X.; Sjodin, T.; Demidov, A. A.; Champion, P. M. Investigations of Coherent Vibrational Oscillations in Myoglobin. J. Phys. Chem. A

2000, 104 (18), 4280–4290. (40)

Liebel, M.; Schnedermann, C.; Kukura, P. Vibrationally Coherent Crossing and Coupling of Electronic States during Internal Conversion in β-Carotene. Phys. Rev.

Lett. 2014, 112 (19). (41)

Schnedermann, C.; Liebel, M.; Kukura, P. Mode-Specificity of Vibrationally Coherent Internal Conversion in Rhodopsin during the Primary Visual Event. J. Am. Chem. Soc.

2015, 137 (8), 2886–2891. (42)

Milota, F.; Prokhorenko, V. I.; Mancal, T.; Von Berlepsch, H.; Bixner, O.; Kauffmann, H. F.; Hauer, J. Vibronic and Vibrational Coherences in Two-Dimensional Electronic Spectra of Supramolecular J-Aggregates. J. Phys. Chem. A 2013, 117 (29), 6007– 6014.

(43)

Sagar, D. M.; Cooney, R. R.; Sewall, S. L.; Kambhampati, P. State-Resolved ExcitonPhonon Couplings in CdSe Semiconductor Quantum Dots. J. Phys. Chem. C 2008, 112 (25), 9124–9127.

(44)

Lin, C.; Gong, K.; Kelley, D. F.; Kelley, A. M. Electron-Phonon Coupling in CdSe/CdS Core/Shell Quantum Dots. ACS Nano 2015, 9 (8), 8131–8141.

(45)

Cederbaum, L. S.; Köppel, H.; Domcke, W. Multimode Vibronic Coupling Effects in Molecules. Int. J. Quantum Chem. 1981, 20 (15 S), 251–267.

(46)

Kumar, A. T. N.; Rosca, F.; Widom, A.; Champion, P. M. Investigations of Amplitude and Phase Excitation Profiles in Femtosecond Coherence Spectroscopy. J. Chem.

Phys. 2001, 114 (2), 701–724. (47)

Rudin, S.; Reinecke, T. L. Temperature-Dependent Exciton Linewidths in Semiconductor Quantum Wells. Phys. Rev. B 1990, 41 (5), 3017–3027.

(48)

Collini, E.; Wong, C. Y.; Wilk, K. E.; Curmi, P. M. G.; Brumer, P.; Scholes, G. D. Coherently Wired Light-Harvesting in Photosynthetic Marine Algae at Ambient Temperature. Nature 2010, 463 (7281), 644–647.

(49)

Malý, P.; Gardiner, A. T.; Cogdell, R. J.; van Grondelle, R.; Mančal, T. Robust Light Harvesting by a Noisy Antenna. Phys. Chem. Chem. Phys. 2018.

(50)

Kirstein, S.; Von Berlepsch, H.; Böttcher, C. Photo-Induced Reduction of Noble Metal Ions to Metal Nanoparticles on Tubular J-Aggregates. Int. J. Photoenergy 2006, 2006.

(51)

Liebel, M.; Schnedermann, C.; Kukura, P. Sub-10-Fs Pulses Tunable from 480 to 980 Nm from a NOPA Pumped by an Yb:KGW Source. Opt. Express 2014, 39 (14), 4112–


Page 20 of 21

Page 21 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4115. (52)

DeLong, K. W.; Trebino, R.; Hunter, J.; White, W. E. Frequency-Resolved Optical Gating with the Use of Second-Harmonic Generation. J. Opt. Soc. Am. B 1994, 11 (11), 2206.

(53)

Schott, S.; Steinbacher, A.; Buback, J.; Nuernberger, P.; Brixner, T. Generalized Magic Angle for Time-Resolved Spectroscopy with Laser Pulses of Arbitrary Ellipticity. J. Phys. B At. Mol. Opt. Phys. 2014, 47 (12).

(54)

Chen, K.; Gallaher, J. K.; Barker, A. J.; Hodgkiss, J. M. Transient Grating Photoluminescence Spectroscopy: An Ultrafast Method of Gating Broadband Spectra.

J. Phys. Chem. Lett. 2014, 5 (10), 1732–1737.


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