58 research outputs found
Nanoplasmonic Colloidal Suspensions for the Enhancement of the Single Walled Carbon Nanotubes Luminescent Emission
Aiming to enhance the luminescence yield of carbon nanotubes, we introduce a
new class of hybrid nanoplasmonic colloidal systems (Ï-hybrids). Nanotubes
dispersed in gold nanorod colloidal suspensions yield hybrid structures
exhibiting enhanced luminescence up to a factor of 20. The novelty of the
proposed enhancement mechanism relies on including metal proximity effects in
addition to its localized surface plasmons. This simple, robust and flexible
technique enhances the luminescence of nanotubes with chiralities whose
enhancement has never reported before, for example the (8,4) tube
Carbon nanotubes for the optical far-field readout of processes that are mediated by plasmonic near-fields
As science progresses at the nanoscopic level, it becomes more and more important to comprehend the interactions taking place at the nanoscale, where optical near-fields play a key role. Their phenomenology differs significantly from the propagative light we experience at the macroscopic level. This is particularly important in applications such as surface-enhanced spectroscopies for single-molecule detection, where often the optimization of the plasmonic structures and surfaces relies on far-field characterizations. The processes dominating in the far-field picture, though, are not the same dominating in the near-field. To highlight this, we resort to very simple metallic systems: isolated gold nanorods in solution. We show how single-walled nanotubes can be exploited to read out processes occurring at the near-field level around metallic nanoparticles and make the information accessible in the far-field region. This is implemented by monitoring the spectral profile of the enhancement of the photoluminescence and Raman signal of the nanotubes for several excitation wavelengths. Through this excitation-resolved study, we show that the far-field optical readout detects the transversal and longitudinal dipolar plasmonic oscillations of gold nanorods, whereas the near-field readout through the nanotubes reveals other mechanisms to dominate. The spectral position of the maximum enhancement of the optical near-field mediated signals are located elsewhere than the far-field bands. This dichotomy between near-field and far-field response should be taken into account when optimizing plasmonic nanostructures for applications such as surface-enhanced spectroscopies
Carbon nanotubes for the optical far-field readout of processes that are mediated by plasmonic near-fields
As science progresses at the nanoscopic level, it becomes more and more important to comprehend the interactions taking place at the nanoscale, where optical near-fields play a key role. Their phenomenology differs significantly from the propagative light we experience at the macroscopic level. This is particularly important in applications such as surface-enhanced spectroscopies for single-molecule detection, where often the optimization of the plasmonic structures and surfaces relies on far-field characterizations. The processes dominating in the far-field picture, though, are not the same dominating in the near-field. To highlight this, we resort to very simple metallic systems: isolated gold nanorods in solution. We show how single-walled nanotubes can be exploited to read out processes occurring at the near-field level around metallic nanoparticles and make the information accessible in the far-field region. This is implemented by monitoring the spectral profile of the enhancement of the photoluminescence and Raman signal of the nanotubes for several excitation wavelengths. Through this excitation-resolved study, we show that the far-field optical readout detects the transversal and longitudinal dipolar plasmonic oscillations of gold nanorods, whereas the near-field readout through the nanotubes reveals other mechanisms to dominate. The spectral position of the maximum enhancement of the optical near-field mediated signals are located elsewhere than the far-field bands. This dichotomy between near-field and far-field response should be taken into account when optimizing plasmonic nanostructures for applications such as surface-enhanced spectroscopies
Effects of Design
Surfactants are needed to create stable suspensions of carbon nanotubes.
Increasingly, these surfactants are given additional functionalities,
resulting in bigger and more complex molecules with several subunits. We
investigate the effect of assembly of these subunits for a class of perylene-
based functional surfactants. The subunits that all surfactants are based on
are a perylene core, hydrophilic polyglycerol dendrons, and alkyl chains of
different orientations and lengths. The assembly of these subunits affects
both the molecules' performance as a surfactant and the efficiency of the
energy-transfer complexes formed by the nanotube and surfactant through a ÏâÏ
stacking mechanism. This results in a best practice guide for designing
functional surfactants with ÏâÏ stacking cores, and affords more general
insights that are applicable to non ÏâÏ stacking systems as well
Excitation characteristics of different energy transfer in nanotube-perylene complexes
We report the properties of perylene-nanotube complexes that form efficient
energy transfer systems. Most perylene-derivatives yield similar ratios
between transfer and direct luminescence (0.66â±â0.04). The photoluminescence
spectra of the free compounds and the transfer complex are similar indicating
that perylene and nanotubes act as separate systems. A further increase in
interaction yields 40% higher transfer rates and luminescence excitation
spectra that indicate a change in stacking of the perylene on the nanotube
wall. All measurements are consistent with a transfer mechanism based on a
dipole-dipole interaction at a distance much smaller than the Förster radius
Controlled reversible debundling of single-walled carbon nanotubes by photo- switchable dendritic surfactants
Stimulus responsive surfactants based on dendritic glycerol azobenzene
conjugates were used to solubilize and debundle single-walled carbon nanotubes
in aqueous media. Their debundling property as well as their reaggregation
behavior upon irradiation with light was examined and light triggered
reversible bundling and precipitation are shown
PlasmonâAssisted Energy Transfer in Hybrid Nanosystems
While direct optical excitation of carbon nanotubes activates only the tube species strictly matching the excitation source, excitation energy transfer processes provide a single excitation channel for all the nanotubes species in a sample. The requirement of an overlap between donor emission and acceptor absorption limits the poll of donors able to trasfer their excitation to the tubes, leaving the highâenergy part of the solar spectrum excluded from such processes. Here it is shown that the grafting of small metal nanoparticles to the tubes alters those rules, enabling energy transfer process from molecules for which the standard energy transfer process is strongly suppressed. The onset of an energy transfer band in the UV/blue spectral region is demonstrated for an hybrid goldâpyreneânanotube system, yielding collective emission from all the tubes present in our samples upon excitation of pyrene
Carbon nanotubes as substrates for molecular spiropyran-based switches
We present a joint theoryâexperiment study investigating the excitonic
absorption of spiropyran-functionalized carbon nanotubes. The
functionalization is promising for engineering switches on a molecular level,
since spiropyrans can be reversibly switched between two different
conformations, inducing a distinguishable and measurable change of optical
transition energies in the substrate nanotube. Here, we address the question
of whether an optical read-out of such a molecular switch is possible.
Combining density matrix and density functional theory, we first calculate the
excitonic absorption of pristine and functionalized nanotubes. Depending on
the switching state of the attached molecule, we observe a red-shift of
transition energies by about 15 meV due to the coupling of excitons with the
molecular dipole moment. Then we perform experiments measuring the absorption
spectrum of functionalized carbon nanotubes for both conformations of the
spiropyran molecule. We find good qualitative agreement between the
theoretically predicted and experimentally measured red-shift, confirming the
possibility for an optical read-out of the nanotube-based molecular switch
Photoswitchable single-walled carbon nanotubes for super-resolution microscopy in the near-infrared
The design of single-molecule photoswitchable emitters was the first milestone toward the advent of single-molecule localization microscopy, setting a new paradigm in the field of optical imaging. Several photoswitchable emitters have been developed, but they all fluoresce in the visible or far-red ranges, missing the desirable near-infrared window where biological tissues are most transparent. Moreover, photocontrol of individual emitters in the near-infrared would be highly desirable for elementary optical molecular switches or information storage elements since most communication data transfer protocols are established in this spectral range. Here, we introduce a type of hybrid nanomaterials consisting of single-wall carbon nanotubes covalently functionalized with photoswitching molecules that are used to control the intrinsic luminescence of the single nanotubes in the near-infrared (beyond 1 ÎŒm). Through the control of photoswitching, we demonstrate super-localization imaging of nanotubes unresolved by diffraction-limited microscopy
Relaxation lifetimes of plasmonically enhanced hybrid gold-carbon nanotubes systems
Recently, we introduced a novel hybridization route for carbon nanotubes using
gold nanoparticles, whose close proximity neatly enhances their radiative
emission. Here we investigate the mechanisms behind the enhancement by
monitoring the de-excitation dynamics of our Ï-hybrids through two-color pump-
probe time-resolved spectroscopy. The de-excitation process reveals a fast
component and a slow component. We find that the presence of gold prominently
affects the fast processes, indicating a stronger influence of the gold
nanoparticle on the intra-band non-radiative relaxation than on the inter-band
recombination of the single-walled carbon nanotube. By evaluating the de-
excitation times, we estimate the balance between near-field pumping and the
faster metal-induced de-excitation contributions, proving the enhanced pumping
to be the leading mechanism
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