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Enhancing the Infrared Response of Carbon Nanotubes from Oligo-Quaterthiophene Interactions Anouar Belhboub, Patrick Hermet, Laurent Alvarez, Rozenn Le Parc, Stephane Rols, Ana Carolina Lopes Selvati, Bruno Jousselme, Yuta Sato, Kazutomo Suenaga, Abdelali Rahmani, and Jean-Louis Bantignies J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b09329 • Publication Date (Web): 30 Nov 2016 Downloaded from http://pubs.acs.org on December 1, 2016

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The Journal of Physical Chemistry

Enhancing the Infrared Response of Carbon Nanotubes From Oligo-Quaterthiophene Interactions A. Belhboub,†,‡ P. Hermet,∗,¶ L. Alvarez,† R. Le Parc,† S. Rols,§ A. C. Lopes Selvati,† B. Jousselme, Y. Sato,⊥ K. Suenaga,⊥ A. Rahmani,‡ and J-L. Bantignies∗,† Laboratoire Charles Coulomb, UMR 5521, Université de Montpellier, CNRS, F-34095 Montpellier, France, Laboratoire d’Etude des Matériaux Avancés et Applications (LEM2A), Université Moulay Ismaïl, Faculté des Sciences, BP 11201, Zitoune, 50000 Meknès, Morocco, Institut Charles Gerhardt Montpellier, UMR 5253 CNRS-UM-ENSCM, Place E. Bataillon, 34095 Montpellier, France, Institut Laue Langevin, 6 Rue Jules Horowitz, B.P. 156, 38042 Grenoble Cédex 9, France, Laboratoire d’Innovation en Chimie des Surfaces et Nanosciences (LICSEN), NIMBE, CEA, CNRS, Université Paris-Saclay, CEA Saclay 91191 Gif-sur-Yvette Cédex, France, and Nanomaterials Research Institute, AIST, Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan E-mail: [email protected]; [email protected]

Abstract ∗ To

whom correspondence should be addressed † Laboratoire Charles Coulomb, UMR 5521, Université de Montpellier, CNRS, F-34095 Montpellier, France ‡ Laboratoire d’Etude des Matériaux Avancés et Applications (LEM2A), Université Moulay Ismaïl, Faculté des Sciences, BP 11201, Zitoune, 50000 Meknès, Morocco ¶ Institut Charles Gerhardt Montpellier, UMR 5253 CNRS-UM-ENSCM, Place E. Bataillon, 34095 Montpellier, France § Institut Laue Langevin, 6 Rue Jules Horowitz, B.P. 156, 38042 Grenoble Cédex 9, France Laboratoire d’Innovation en Chimie des Surfaces et Nanosciences (LICSEN), NIMBE, CEA, CNRS, Université Paris-Saclay, CEA Saclay 91191 Gif-sur-Yvette Cédex, France ⊥ Nanomaterials Research Institute, AIST, Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan

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Infrared response on a carbon nanotube is weak because this homonuclear allotrope of carbon does not bear permanent dipoles. Here, we report the discovery of an exaltation of the infrared absorption response in single-walled carbon nanotubes from dye molecule interactions. Study performed on dimethylquaterthiophene confined into the hollow core of single-walled carbon nanotubes or π-stacked at the outer surface of the latters leads to a symmetry breaking allowing to probe interactions between both sub-systems. The nature of these interactions is discussed taking into account the tube diameter. This new phenomenon opens a new route to detect weak vibrations thanks to confinement effect.

I. Introduction Mid-infrared (MIR) spectroscopy of single-walled carbon nanotubes (SWCNT) has been neglected in the past. Indeed, MIR response on a carbon nanotube is weak (see Fig. S1) because this homonuclear allotrope of carbon does not bear permanent dipoles. 1–6 Nevertheless, a significant number of infrared phonons are predicted by the group theory. Previous MIR investigations of carbon nanotubes after chemical doping have shown that the phonon bands exhibit an asymmetric line shape and that their effective cross section is enhanced upon chemical doping. 1 Encapsulating molecules inside SWCNTs (called hybrid nanotubes in the following) is a common strategy to add new functionalities. The one-dimensional nature of SWCNTs internal channels has been exploited to induce a molecular order that leads to an enhancement of the nonlinear response 7 and give rise to a giant Raman scattering effect. 8 When encapsulated, single molecule magnets inside the nanotube undergo a large degree of orientational ordering and the magnetic guest molecules influence the electrical resistance of the host nanotubes. 9 Here we report the discovery of a strong dependence on the infrared response of the hybrid nanotube (4T@NT) due to confinement effect when dimethylquaterthiophenes (4T) are encapsulated inside SWCNTs. Results are also compared to experiments performed on nanotubes where 4T are π-stacked at the outer surface (4T-π-NT). Surprisingly, a strong infrared band assigned to a radial mode of the nanotubes is exhibited in hybrid nanotubes whereas the intensity of this band 2 ACS Paragon Plus Environment

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is weak in pristine nanotubes. Thanks to the comparison between the experimental spectra and the calculated ones, we elucidate the origin of the large enhancement of this infrared absorption and demonstrate that interactions between conjugated oligomers and nanotubes can be probed. Influence of the endohedral or external non covalent functionalization is also presented. This large absorption is a new phenomenon specific to non covalent functionalization of nanotubes with oligothiophenes. This suggests a means of developing solar absorbers for energy harvesting, sensitive bandpass filters or resonant detectors.

II. Experimental section II.A. Sample preparation Two sources of nanotubes have been used in this study: commercial electric arc single-walled carbon nanotubes (1.2 nm < d < 1.6 nm) provided by Carbon Solution 10 (called NT14 in the following) and CoMoCAT carbon nanotubes enriched in (7,6) chirality (0.6 nm < d < 1 nm) 11 (called NT09 in the following). The nanotube samples were purified by air oxidation and subsequently treated to remove the catalyst. Encapsulation of 4T into carbon nanotubes was performed using the vapor reaction method previously described. 12 Before the encapsulation treatment, carbon nanotubes were outgassed at 300◦ C for 48h. Then, NTs were mixed with 4T in the weight ratio ωNT s /ω4T = 0.5 in the glovebox and outgassed under 2×10−6 mbar at ambient temperature for 1h. Then, NTs with 4T were sealed in glass tube at 2×10−6 mbar and heated to 250◦ C for 72h. The sublimation step was then performed. The sample was then washed with organic solvent and stored in the oven at 120◦ C for 24h. The hybrid material is named 4T@NT in the following. To prove the encapsulation of 4T inside the hollow core of the nanotubes, transmission electron microscopy (TEM) studies were performed on the hybrid nanotubes. High resolution (HR) TEM micrographs display SWCNTs filled with presumably 4T. For 4T@NT14 the contrast is coherent with the presence of two lines of molecules face to face inside the tubes (Fig. S5-left) and for 4T@NT09 only one line of molecules is exhibited (Figs. S5-right and S6-left). These results are 3 ACS Paragon Plus Environment


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in agreement with previous investigation. 13 In order to go further in the analysis of these materials and to know where the 4T molecules are localized, Spatial-Resolved Electron Energy-Loss Spectroscopy (SR-EELS) experiments combined with scanning TEM (STEM) were performed. The marked area in the annular dark field (ADF) STEM image (Fig. S6-left) corresponds to domains where EEL spectrum imaging is performed. Chemical maps of carbon and sulfur have been extracted from intensities of Carbon K edge and L2,3 edge of sulfur. It appears that sulfur (from 4T) is not surrounding the nanotubes but is localized within the hollow core of the tubes giving thus insights on the quality of the encapsulation procedure. Fig. S6-right shows a typical EEL spectrum recorded at the point where sulfur exists in the areas marked in Fig. S6-left. The energy loss near-edge feature (ELNES) of the C-K edge consists of a π ∗ peak at ∼285 eV and a well-defined σ ∗ band starting at ∼292 eV. The S-L2,3 edge consist of a rather large peak around 165-220 eV. Figure S7 displays the Raman spectra of pristine and hybrid nanotubes (4T@NT09 and 4T@NT14) for the 501.7 nm excitation wavelength. The low frequency bands (100-300 cm−1 ) correspond to the radial breathing (RBM) modes whose positions depend on the nanotube diameter. We use the following relationship 14 to derive the mean diameter probed: ωRBM (cm−1 ) = 218/d(nm) + 17. For 4T@NT09 (4T@NT14), the RBM positions are respectively at 262 and 268 cm−1 (163 and 176 cm−1 ) and correspond to mean diameters of 0.89 and 0.94 nm (1.49 and 1.37 nm). Due to resonance effect, characterizations with others laser excitation wavelengths were used and the results lead to the same diameter distributions. The high frequency region displays modes lying in the 1400-1500 cm−1 range and corresponding to the carbon-carbon stretching of the 4T molecules 12 are 1449 and 1481 cm−1 . The Raman G+ -bands of the nanotubes are located around 1590 cm−1 . For the 4T@NT14, the profile corresponds to semiconducting nanotubes. For the 4T@NT09, it corresponds to the response of both semiconducting and metallic nanotubes highlighting the presence of numerous chiralities in the sample. It is worth mentioning that no photoluminescence of the 4T molecules is observed once encapsulated, meaning that all the molecules strongly interact with the nanotubes. This assumption is confirmed by the RBM shifts.


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II.B. Infrared spectroscopy Mid-infrared spectra are performed in transmittance between 830 and 650 cm−1 on a Bruker IFS66V Fourier transform spectrometer working under vacuum. The apparatus is equipped with a KBr beam-splitter and a Deuterated Triglycine Sulfate (DTGS) detector. We used a resolution of 4 cm−1 and 512 scans were co-added for each spectrum. Absorbance is obtained as A = −log(I/I0 ) where I is the sample single beam spectrum and I0 is the reference single beam spectrum. The sample is ground with KBr (0.5 mg/300 mg) and compressed under 8 tons to form isotropic pellets of 13 mm diameter. Baseline is taken between 4000 and 500 cm−1 (see Fig. S2). A fourth order polynomial is fitted through points selected where no band is observed, and subtracted from the original data (see Fig. S4). In the following, the vibrational study focus on the radial vibration region of the tubes (600-900 cm−1 ) as high frequency region is known to be very influenced by carboneous defects 2 and absorbed water vibrations. Spectra of hybrid nanotubes are normalized to the most intense band centered at ∼780 cm−1 (see Fig. S4).

III. Computational details Density functional theory (DFT) based calculations are performed with the SIESTA package 15 and the generalized gradient approximation to the exchange correlation functional as proposed by Perdew, Burke and Ernzerhof. 16 Core electrons are replaced by nonlocal norm-conserving pseudopotentials. 17 The valence electrons are described by a double-ζ singly polarized basis set. 18 The localization of the basis is controlled by an energy shift of 50 meV. Real space integration is performed on a regular grid corresponding to a plane-wave cutoff of 300 Ry. Only the Γ-point is taken into account for the one-dimensional Brillouin zone integrations. Van der Waals corrections (DFT-D) between the nanotube and the molecule are considered using the semi-empirical dispersion potentiel parametrized by Grimme. 19 For the two encapsulated systems, 4T@NT09 and 4T@NT14, we respectively considered in our calculations two model systems: the 4T@(11,0) where only one 4T molecule is placed inside the (11,0) nanotube and the 4T@(17,0) where two 5 ACS Paragon Plus Environment


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molecules are placed inside the (17,0) nanotube. The initial position of the 4T molecule(s) was chosen according to the energy minimization performed by Loi et al. 20 For the π-stacked system, we considered the (17,0) nanotube as model of the experimental 4T-π-NT14. We chose these zigzag nanotubes as model systems because they are semiconducting, their diameters are similar to the mean diameters experimentally observed and their number of atoms is still reasonable for DFT calculations in contrast to chiral tubes. We fixed the nanotube length to 29.82 Å and a vaccum size of 11 Å was used to avoid interactions between adjacent tubes. Thus, the 4T@(11,0), 4T-π-(17,0) and 4T@(17,0) have 344, 512 and 548 atoms in our calculations, respectively. Atomic positions were relaxed using a conjugate gradient until the maximum residual atomic force was smaller than 0.02 eV/Å. Structures and characteristic distances after relaxation of these three model systems are displayed in Fig. 1. The zone-center dynamical matrices are calculated within the harmonic approximation by finite difference of the Hellmann-Feynman forces using an atomic displacement of 0.03 Å. Positive and negative displacements are used to minimize the anharmonic effects. The infrared spectra is calculated as: 21 2π 2 I= 3Ω0 nc ∑ j

qκ ∑ √Mκ e j (κ) κ

2 δ (ω − ω j ),

(1)

where the sum over κ runs over all atoms κ of the unit cell with mass Mκ . Ω0 , n, c and qκ are the unit cell volume, the refractive index, the velocity of light and the Bader charge of atom κ, respectively. Here, Bader static charges have been used instead of the usual Born effective charge tensors because the latter require too high computational time to be calculated using the modern theory of polarization. e j (κ) and ω j are the eigenvectors and the frequencies of the j-th normal mode obtained by diagonalization of the dynamical matrix.

IV. Results and discussion The experimental mid-infrared spectrum of the 4T@NT14, displayed within the region of the radial modes of the tubes (Fig. 2(b)-left), is dominated by two strong bands at 688 and 788 cm−1 . 6 ACS Paragon Plus Environment

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Four weak and broad bands are also observed at 668, 719, 743 and 815 cm−1 . Since the oscillator strengths of the nanotube modes are expected to be weak in this domain (see Fig. S3), all these contributions should come from the 4T molecules. The profile of the experimental 4T spectrum in THF solution is reported in Fig. 2(d)-left. This spectrum indeed shows strong similarities with the one of the 4T@NT14 concerning the number of bands. A simple filiation procedure between the bands of the 4T@NT14 and those of the 4T provides the assignment of all the bands except the one at 719 cm−1 that has not its counterpart in the 4T spectrum. In addition, the two first bands below 690 cm−1 in the 4T spectrum, which should be associated by filiation to the bands at 668 and 688 cm−1 in the 4T@NT14 spectrum, have their relative intensities strongly affected by the encapsulation while those of the other bands are preserved. This change in intensity coupled with the absence of a band at about 720 cm−1 in the 4T spectrum therefore raises some questions on the 4T@NT14 mode assignment considering only the phonon modes of the 4T molecule. At this stage, the understanding of the 4T@NT14 infrared response from only the experimental data seems complex and a theoretical support proves to be necessary. In this context, the infrared spectrum has been calculated on the 4T@(17,0) whose diameter is close to the mean diameter of the 4T@NT14 observed in our measurements. This calculated spectrum, displayed in Fig. 2(b)-right, shows that the number of the bands and their relative intensities are in excellent agreement with the experiment. This correspondence between our calculations and the experimental observations suggests a reliable assignment of the experimental bands. To have a deeper insight on the participation of each sub-system, the sum over κ in Eq. (1) has been decomposed as (with a simplified notation):

∑ κ

2

=

∑

NT

2

+

∑

4T1

2

+

∑

4T2

2

+2

∑∑+∑∑+∑∑

NT 4T1

NT 4T2

,

(2)

4T1 4T2

where the three first terms are respectively the responses of the (17,0) nanotube (NT), the first 4T molecule and the second 4T molecule while the three last terms are the coupling terms which describe the responses associated to the interactions between the (17,0) and the 4T or the interactions



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between the 4T molecules (see Fig. 1(b)). This decomposition, given in Fig. 3-middle, shows that the calculated (17,0) contribution in the hybrid system has more bands between 580 and 900 cm−1 than the single E1u radial band expected in the pure (17,0) nanotube (Fig. 2(h)-right). This single E1u band calculated in pure nanotubes is consistent with the experimental data reported in the literature within this frequency range. 2 The infrared-active additionnal bands of the (17,0) contribution in 4T@(17,0) originate from a symmetry breaking of the infrared selection rules of the nanotube due to the 4T encapsulation as the coupling between the 4T and the nanotube is important for these frequencies (see the NT/4T coupling terms in Fig. 3-middle). In the case of the 4T molecules, this symmetry breaking plays a much minor role. Indeed, we do not observe additional bands with respect to the isolated molecule (see Fig.2(g)-right) and the relative intensity of bands slightly changes. The infrared responses of the two 4T molecules in 4T@(17,0) are similar, suggesting that they cannot be distinguished. The assignment of the experimental bands are performed using the different calculated contributions of each sub-system (Fig. 3-middle) and by analyzing the eigendisplacement vectors obtained from the diagonalization of the dynamical matrix. The experimental band at 688 cm−1 , associated to the calculated band at 631 cm−1 , is assigned to an in-plane breathing of thiophene rings coupled with the deformation of the nanotube. The experimental band at 743 cm−1 , associated to the calculated band at 769 cm−1 , can be mainly assigned to the nanotube (the contribution of the 4T molecules is small). The examination of the calculated eigendisplacement vectors shows that this band is assigned to a radial motion of the nanotube coupled to a C-H wagging of the molecule. The broad experimental band at 788 cm−1 , associated to the calculated band at 823 cm−1 , can be mainly associated to the (17,0) nanotube with a small participation of the 4T molecule. Our calculations show that this band mainly comes from the E1u radial mode in pure (17,0) calculated at 836 cm−1 as their eigendisplacement vectors overlap by ∼ 85 %. The experimental counterpart of this mode is very difficult to detect (see Fig. S3). This band is therefore assigned to an asymmetric radial motion which is slightly different from the perfectly symmetric E1u radial mode in a pure nanotube because of the molecule/nanotube interactions (see Fig. 4). As a consequence, the inten-


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sity of this band is more intense in 4T@(17,0) than in pure (17,0) due to an enhancement of the mode polarity (with respect to the pure (17,0) nanotube) which is not compensated by the renormalization by the volume (see Eq. (1)). Furthermore, this band undergoes a frequency downshift of 13 cm−1 with respect to pure (17,0) which could be explained by hybridization effects between the two sub-systems or by a charge transfer from 4T to the nanotube. The remaining experimental bands involve mainly the 4T molecules and their assignments are listed in Table 1. In the case where the 4T molecule is π-stacked at the outer surface of the nanotube, the experimental infrared response is identical (at least at the first order) to that observed for the encapsulation (see Fig. 2(b)-left and Fig. 2(c)-left). In particular, we do not observe a frequency shift of the radial mode at 788 cm−1 (inset of Fig. 2-left). These experimental observations are in agreement with our calculations. In addition, the calculated decomposition reported in Fig. 3 shows that the infrared response of each sub-system is also quite similar between the 4T@(17,0) and the 4T-π(17,0). Thus, a possible explanation is that the 4T molecule is almost at the same distance from the nanotube wall whether it is π-stacked or inside the (17,0) nanotube (see Fig. 1), resulting in similar intersystem interactions as the curvature effect is weak for the (17,0) SWCNT. When the diameter of the nanotube decreases down to 0.9 nm, a single 4T molecule can be placed inside the nanotube. 12 In this case, the intensity of the 4T infrared bands seems more affected. Indeed, the experimental 4T@NT09 infrared spectrum shows a broad unresolved contribution below 750 cm−1 (see Fig. 2(a)-left). In this range, the calculated spectrum is more resolved as four weak bands are predicted at 633, 673, 715 and 742 cm−1 (see Fig. 2(a)-right). Their positions can be clearly identified with respect to the calculated 4T@(17,0) spectrum. However, their relative intensities are not conserved, especially for the first one that decreases in the 4T@(11,0) in agreement with the experimental behavior. This is due to a negative coupling term which is maximized for small diameters between the 4T and the nanotube (see Fig. 3-left). In this case, the hybrid system exhibits only in-plane breathing of 4T. Moreover, the radial motion coupled to CH wagging is significantly downshifted under confinement. Above 750 cm−1 , the experimental 4T@NT09 spectrum is similar to that of the 4T@NT14 with a single band at 786 cm−1 . This band,



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associated to the radial mode in pure nanotube, shows a weak downshift of 2 cm−1 with respect to the 4T@NT14. This dependence is well reproduced by our calculations although it is slightly overestimated. Our calculations show that the frequency downshift of this band when the tube diameter decreases is purely associated to a diameter effect. Indeed, we observe exactly the same shift in pure nanotubes for the E1u radial mode (see Fig. 2 (h) and (i)). To go further, we evaluated the charge transfer between the nanotube and the molecules as follows: Δρ = ρhybride − ρtube − ρmolecule(s) , where the densities of the nanotube, ρtube , and the molecule(s), ρmolecule(s) , have been computed in the same geometry as that of the hybrid nanotube, ρhybride . This charge density difference is depicted in Fig.5 for the 4T@(11,0) and 4T@(17,0). The electronic exchange occurs mainly in a “face-to-face” configuration between 4T and the nanotube walls in 4T@NT14, which could also explain the identical inter-system interaction between 4T@(17,0) and 4T-π-(17,0). In contrast, for 4T@(11,0), the interactions between 4T and the nanotube wall mainly occur through sulfur atoms due to the confinement effect. Another indication of this confinement effect is given by the comparison of the calculated infrared spectra between 4Tπ-(11,0) and 4T@(11,0) (see Fig. S7). In contrast to the case of large nanotubes, these two spectra show significant differences as the 4T-π-(11,0) spectral profile is closer to that of 4T@(17,0).

V. Conclusions In conclusion, mid-infrared spectra were adressed both theoretically and experimentally in 4T@NT and 4T-π-NT systems. First, the good agreement between the experimental and calculated spectra allows us to assign the main infrared bands of these systems. Then, the contribution of each sub-system to the total infrared response of the hybrid system has been calculated. Our calculations show that both sub-systems are extremely affected by the encapsulation in small hybrid nanotubes (diameter below 1 nm). Indeed, the relative intensities of the encapsulated 4T infrared bands change in comparison to those of the isolated molecule. Moreover, the nanotube exhibits new additional bands in the hybrid system as only the E1u radial mode is expected in pure nan-


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otubes within the 900-580 cm−1 range. This was explained by a symmetry breaking of the infrared selection rules of the nanotube resulting from the interaction with the molecules. In addition, we observe the enhancement of the intense band calculated at 811 cm−1 (786 cm−1 experimentally) which was assigned to a “radial-like” mode. This increase in intensity is correlated to the mode oscillator strength increase relative to pristine nanotubes, suggesting an electronic doping from 4T to nanotubes. This hypothesis will be explored in details in the future. The decomposition of the infrared spectra has also shown that the coupling term becomes less important when the diameter of the nanotube is increased. Finally, no differences were significantly seen in the infrared response of 4T-π-(17,0) in comparison to 4T@(17,0) as the interaction mechanism remains the same. This was also shown from electronic density calculations. However, this similitude tends to vanish when the nanotube diameter decreases because of stronger confinement effects.

Supporting Information Synthesis of 4T and additional experimental spectra (infrared, Raman, HR-TEM, SR-EELS, STEM) of pristine and hybrid compounds are given in supporting information.

Acknowledgment YS and KS acknowledge financial support from JSPS KAKENHI (grant number JP16K05948) and JST Research Acceleration Program.

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(2) Bantignies, J. L.; Sauvajol, J. L.; Rahmani, A.; Flahaut, E. Infrared-Active Phonons in Carbon Nanotubes. Phys. Rev. B 2006, 74, 195425. (3) Kuhlmann, U.; Jantoljak, H.; Pfänder, N.; Bernier, P.; Journet, C. Thomsen, C. Infrared Active Phonons in Single-Walled Carbon Nanotubes. Chem. Phys. Lett. 1998, 294, 237-240. (4) Bermudez, V. M. Adsorption on Carbon Nanotubes Studied Using Polarization-Modulated Infrared Reflection-Absorption Spectroscopy. J. Phys. Chem. B 2005, 109, 9970-9979. (5) Kim, U. J.; Furtado, C. A.; Liu, X.; Chen, G.; Eklund, P. C. Raman and IR Spectroscopy of Chemically Processed Single-Walled Carbon Nanotubes. J. Am. Chem. Soc. 2005, 127, 15437-15445. (6) Pekker, A.; Botos, A.; Rusznyák, A.; Koltai, J.; Kürti, J. Kamarás, K. Vibrational Signatures in the Infrared Spectra of Single- and Double-Walled Carbon Nanotubes and Their Diameter Dependence. Phys. Chem. Lett. 2011, 2, 2079-2082. (7) Cambré, S.; Campo, J. -L.; Beirnaert, C.; Verlackt, C.; Cool, P.; Wenseleers, W. Asymmetric Dyes Align inside Carbon Nanotubes to Yield a Large Nonlinear Optical Response. Nature Nanotechnology 2015, 10, 248-252. (8) Gaufrès, E.; Tang, N. Y. W.; Lapointe, F.; Cabana, J.; Nadon, M. A.; Cottenye, N.; Raymond, F.; Szkopek, T.; Martel, R. Giant Raman Scattering from J-Aggregated Dyes inside Carbon Nanotubes for Multispectral Imaging. Nature Photonics 2013, 8, 72-78. (9) Giménez-López, M. C.; Moro, F.; La Torre, A.; Gómez-Garcia, C. J.; Brown, P. D.; van Slageren, J.; Khlobystov, A. N. Encapsulation of Single-Molecule Magnets in Carbon Nanotubes. Nature Communications 2011, 2, 407. (10) Carbon Solution Inc., http://www.carbonsolution.com. (11) http://www.sigmaaldrich.com.


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(12) Alvarez, L.; Almadori, Y.; Arenal, R.; Babaa, R.; Michel, T.; Le Parc, R.; Bantignies, J. -L.; Jousselme, B.; Palacin, S.; Hermet, P. et al. Charge Transfer Evidence between Carbon Nanotubes and Encapsulated Conjugated Oligomers. J. Phys. Chem. C 2011, 115, 1189811905. (13) Almadori, Y.; Alvarez, L.; Le Parc, R.; Aznar, R.; Fossard, F.; Loiseau, A.; Jousselme, B.; Campidelli, S.; Hermet, P.; Belhboub, A. et al. Chromophore Ordering by Confinement into Carbon Nanotubes. J. Phys. Chem. C 2014, 118, 19462-19468. (14) Araujo, P. T.; Doorn, S. K.; Kilina, S.; Tretiak, S.; Einarsson, E.; Maruyama, S.; Chacham, H.; Pimenta, M. A.; Jorio, A. Third and Fourth Optical Transitions in Semiconducting Carbon Nanotubes. Phys. Rev. Lett. 2007, 98, 067401. (15) Sanchez-Portal, D.; Ordejon, P.; Artacho, E.; Soler, J.M. Density-Functional Method for Very Large Systems with LCAO Basis Sets. Int. J. Quantum Chem. 1997, 65, 453-461. (16) Perdew, J.P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865-3868. (17) Troullier, N.; Martins, J.L. Efficient Pseudopotentials for Plane-Wave Calculations. Phys. Rev. B 1991, 43, 1993-2006. (18) Artacho, E.; Sanchez-Portal, D.; Ordejon, P.; Garcia, A.; Soler, J.M. Linear-Scaling Ab-Initio Calculations for Large and Complex Systems. Phys. Status Solidi B 1999, 215, 809-817. (19) Grimme, S. Semiempirical GGA-type Density Functional constructed with a Long-range Dispersion Correction. J. Comput. Chem. 2006, 27, 1787-1799. (20) Loi, M.A.; Gao, J.; Cordella, F.; Blondeau, P.; Menna, E.; Bartova, B.; Hebert, C.; Lazar, S.; Botton, G.A.; Milko, M. et al. Encapsulation of Conjugated Oligomers in Single-Walled Carbon Nanotubes: Towards Nanohybrids for Photonic Devices. Adv. Mater. 2010, 22, 16351639. 13 ACS Paragon Plus Environment


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(21) Maradudin, A.A.; Montroll, E.W.; Weiss, G.H.; Ipatova, I.P. Theory of Lattice Dynamics in the Harmonic Approximation. Academic Press; New York, 1971. (22) Joung, S.-K.; Okazaki, T.; Kishi, N.; Okada, S., Bandow, S.; Iijima, S. Effect of Fullerene Encapsulation on Radial Vibrational Breathing-Mode Frequencies of Single-wall Carbon Nanotubes. Phys. Rev. Lett. 2009, 103, 027403.


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Table 1: Calculated and experimental frequencies in the 600–900 cm−1 range of the most intense infrared bands (in cm−1 ) in 4T@(11,0), 4T@(17,0) and 4T-π-NT14 with their proposed assignment. 4T@(11,0) Exp. Calc.

4T@(17,0) Exp. Calc.

4T-π-(17,0) Exp. Calc.

687

633

688

631

688

631

722 741 786 820

673 715 742 811 866

719 743 788 815

665 715 769 823 874

719 744 788 815

665 715 769 823 874

Proposed Assignment in-plane breathing of thiophene rings for 4T@(11,0) coupled with NT deformation for 4T@(17,0) and 4T-π-(17,0) in-plane breathing of thiophene rings in-plane deformation of thiophene rings radial motion of NT coupled to C-H wagging asymetric radial motion of the nanotube in-plane deformation of thiophene rings



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(b)

(a)

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(c) ૞Ǥ ૙

૜Ǥ ૝

૜Ǥ ૜ ૝Ǥ ૚

૟Ǥ ૟

૜Ǥ ૝

Figure 1: Calculated relaxed structures of (a) 4T@(11,0), (b) 4T@(17,0) and (c) 4T-π-(17,0). The highlighted distances are given in Å.


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Figure 2: Exprimental (calculated) infrared spectra of (a) 4T@NT09 (4T@(11,0)), (b) 4T@NT14 (4T@(17,0)) and (c) 4T-π-NT14 (4T-π-(17,0)). Insets highlight the frequency shift of the most intense band. The experimental 4T spectrum in THF solution is diplayed in (d). The experimental spectra of pristine NT14 and NT09 are given in (f) and (e), respectively. Calculated infrared spectrum of (h) pristine (17,0), (i) pristine (11,0) and (g) isolated 4T molecule. Calculated spectra are at 0 K and they are displayed using a Lorentzian lineshape with 20 cm−1 linewidth. Experimental spectra have been measured at room temperature.



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Figure 3: (Upper panels) Contribution of each sub-system to the infrared response in 4T@(11,0), 4T@(17,0) and 4T-π-(17,0). Each spectrum has been normalized according to 0∞ I(ω)dω = 1 and displayed using a linewidth of 20 cm−1 . (Bottom panels) Coupling terms associated to the interactions between the nanotube and the 4T molecule(s). In the of 4T@(17,0), we have the additional interaction between the 4T molecules (see text).


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Figure 4: Calculated eigendisplacements vectors for the E1u radial mode at 836 cm−1 in pure (17,0) and the asymmetric radial mode at 823 cm−1 in 4T@(17,0).



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Figure 5: Electronic charge density difference with isovalues of +0.0003 (red) and -0.0003 (blue) electrons per angstrom3 .


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Enhancing the Infrared Response of Carbon ... - ACS Publications

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