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Measuring electronic Raman scattering (ERS) has become an efficient method for structural characterization of metallic single-wall carbon nanotubes (SWCNT). However, applying this method to other types of SWCNT-based structures, e.g., those with strong van der Waals (VDW) coupling, is currently not well studied. In this work, we combine electron diffraction, Rayleigh and Raman spectroscopies to investigate the ERS process near 36 metallic transitions in 21 individual double-wall carbon nanotubes (DWCNTs) with all types of electronic configurations. We observe the partial suppression of ERS intensity in DWCNTs compared to SWCNTs and mainly attribute it to the effect of dielectric screening of Coulomb interactions. We probe ultra-pure macroscopic multi-chirality DWCNT solutions and identify the role of inhomogeneous broadening in observing ERS peaks in Raman spectra. Based on the experimental findings, we propose an adapted method for the structural identification of DWCNT samples from the ERS data. The obtained results can be generalized to the characterization of the emerging 1D VDW heterostructures based on metallic SWCNTs., DL thanks Prof. S. Rochal and D. Chalin for providing MAPLE code for calculating DWCNT transition energy shifts and W. Van Werveke and M. De Clercq for providing MATLAB code for creating chirality distribution maps. A part of the experimental data (i.e., microscopic Rayleigh and Raman spectra, ED patterns) was obtained and preliminary processed within the framework of Russian Foundation for Basic Research grant 18-32-00397 mol_a. Further data analysis (i.e., developing models for ERS, Raman and Rayleigh spectra fitting) was performed by DL with the support of the postdoctoral grant (12ZP720N) of the Fund for Scientific Research Flanders (FWO). The TEM measurements were performed in the Laboratorio de Microscopias Avanzadas (LMA), Universidad de Zaragoza (Spain). R.A. gratefully acknowledges the support from the Spanish MICINN (PID2019-104739 GB-100/AEI/10.13039/501100011033), Government of Aragon (projects DGA E13-20R (FEDER, EU)) and from the European Union H2020 program “ESTEEM3” (Grant number 823717). V.N.P. acknowledges financial support for NTB calculations from the National Science Fund of Bulgaria under grant KP-06-N38/10 from 06.12.2019. T.T.C acknowledges financial support from Vietnam Academy of Science and Technology (grant number: VAST03.06/22-23). H.N.T, E.F., A.A.Z, J.L.S. and M.P. acknowledge financial support by the ANR GAMBIT project, grant ANR-13-BS10-0014 of the French Agence Nationale de la Recherche. The characterization of the macroscopic UP-DWCNT samples was financially supported by a PhD fellowship for M. Erkens of the Research Foundation of Flanders (FWO, grant number: 11C9220N). D.L. acknowledges the financial support from the University of Antwerp Research Fund (grant BOF KP 43770). D.L., M.A., W.W. and S.C. also acknowledge funding from FWO projects (G040011N, G02112N, G035918N and G036618N).

The coaxial stacking of two single-wall carbon nanotubes (SWCNTs) into a double-wall carbon nanotube (DWCNT), forming a so-called one-dimensional van der Waals structure, leads to synergetic effects that dramatically affect the optical and electronic properties of both layers. In this work, we explore these effects in purified DWCNT samples by combining absorption, wavelength-dependent infrared fluorescence–excitation (PLE), and wavelength-dependent resonant Raman scattering (RRS) spectroscopy. Purified DWCNTs are obtained by careful solubilization that strictly avoids ultrasonication or by electronic-type sorting, both followed by a density gradient ultracentrifugation to remove unwanted SWCNTs that could obscure the DWCNT characterization. Chirality-dependent shifts of the radial breathing mode vibrational frequencies and transition energies of the inner and outer DWCNT walls with respect to their SWCNT analogues are determined by advanced two-dimensional fitting of RRS and PLE data of DWCNT and their reference SWCNT samples. This exhaustive data set verifies that fluorescence from the inner DWCNT walls of well-purified samples is severely quenched through efficient energy transfer from the inner to the outer DWCNT walls. Combined analysis of the PLE and RRS results further reveals that this transfer is dependent on the inner and outer wall chirality, and we identify the specific combinations dominant in our DWCNT samples. These obtained results demonstrate the necessity and value of a combined structural characterization approach including PLE and RRS spectroscopy for bulk DWCNT samples.

The excitonic structure of single-wall carbon nanotubes (SWCNTs) is chirality dependent and consists of multiple singlet and triplet excitons (TEs) of which only one singlet exciton (SE) is optically bright. In particular, the dark TEs have a large impact on the integration of SWCNTs in optoelectronic devices, where excitons are created electrically, such as in infrared light-emitting diodes, thereby strongly limiting their quantum efficiency. Here, we report the characterization of TEs in chirality-purified samples of (6,5) and (7,5) SWCNTs, either randomly oriented in a frozen solution or with in-plane preferential orientation in a film, by means of optically detected magnetic resonance (ODMR) spectroscopy. In both chiral structures, the nanotubes are shown to sustain three types of TEs. One TE exhibits axial symmetry with zero-field splitting (ZFS) parameters depending on SWCNT diameter, in good agreement with the tighter confinement expected in narrower-diameter nanotubes. The ZFS of this TE also depends on nanotube environment, pointing to slightly weaker confinement for surfactant-coated than for polymer-wrapped SWCNTs. A second TE type, with much smaller ZFS, does not show the same systematic trends with diameter and environment and has a less well-defined axial symmetry. This most likely corresponds to TEs trapped at defect sites at low temperature, as exemplified by comparing SWCNT samples from different origins and after different treatments. A third triplet has unresolved ZFS, implying it originates from weakly interacting spin pairs. Aside from the diameter dependence, ODMR thus provides insights in both the symmetry, confinement, and nature of TEs on semiconducting SWCNTs.

Being some of the most efficient agents to individually solubilize single-wall carbon nanotubes (SWCNTs), bile salt surfactants (BSS) represent the foundation for the surfactant-based structure sorting and spectroscopic characterization of SWCNTs. In this work, we investigate three BSS in their ability to separate different SWCNT chiral structures by aqueous two-phase extraction (ATPE): sodium deoxycholate (DOC), sodium cholate (SC) and sodium chenodeoxycholate (CDOC). The small difference in their chemical structure (just one hydroxyl group) leads to significant differences in their stacking behavior on SWCNT walls with different diameter and chiral structure that, in turn, has direct consequences for the chiral sorting of SWCNTs using these BSS. By performing several series of systematic ATPE experiments, we reveal that, in general, the stacking of DOC and CDOC is more enantioselective than the stacking of SC on the SWCNT walls, while SC has a clear diameter preference for efficiently solubilizing the SWCNTs in comparison to DOC and CDOC. Moreover, combining sodium dodecylsulfate with SC allows for resolving the ATPE sorting transitions of empty and water-filled SWCNTs for a number of SWCNT chiralities. We also show that addition of SC to combinations of DOC and sodium dodecylbenzenesulfonate can enhance separations of particular chiralities.

Aqueous two-phase (ATP) extraction has been demonstrated as a fast, scalable, and effective separationtechnique to sort single-wall carbon nanotubes (SWCNTs) according to their diameter and chiral structure.The exact mechanism behind the chirality-dependent migration of SWCNTs between the twophases is however not completely understood, and depends on many parameters (e.g., choice of surfactantsand their concentration, pH, temperature, …), making it difficult to optimize the multivariableparameter space. In this work, we present a systematic study of the choice and concentration of specificsurfactants on the ATP sorting, by performing a series of single-step ATP separations in which each timeonly one parameter is systematically varied, while monitoring the structure-specific migration of everySWCNT chirality between both phases with detailed wavelength-dependent spectroscopy. These systematicstudies reveal that the diameter-dependent stacking of a discrete number of sodium deoxycholatemolecules fitting around the SWCNT circumference determines the separation order in the formof a periodically modulated pattern as a function of SWCNT diameter. Addition of cosurfactants can beused to compete with the bile salt surfactant to enhance the separation yields, but does not affect thesorting order. The results are afterwards directly applied to predict the parameters required to separatespecific chiral structures in just two ATP steps.

The filling of single-wall carbon nanotubes (SWCNTs) with dye molecules has become a novel path toadd new functionalities through the mutual interaction of confined dyes and host SWCNTs. In particularcases, the encapsulated dye molecules form strongly interacting molecular arrays and these result inseverely altered optical properties of the dye molecules. Here, we present the encapsulation of a squarainedye inside semiconducting chirality-sorted SWCNTs with diameters ranging from ∼1.15 nm, in whichthe dye molecules can only be encapsulated in a single-file molecular arrangement, up to ∼1.5 nm, inwhich two or three molecular files can fit side-by-side. Through the chirality-selective observation ofenergy transfer from the dye molecules to the surrounding SWCNTs, we find that the absorption wavelengthof the dye follows a peculiar SWCNT diameter dependence, originating from the specific stackingof the dye inside the host SWCNTs. Corroborated by a theoretical model, we find that for each SWCNTdiameter, the dye molecules adopt a close packing geometry, resulting in tunable optical properties ofthe hybrid when selecting a specific SWCNT chirality.

The unusually chiral-structure-dependent properties of single-wall carbon nanotubes (SWCNTs) are also strongly influenced by their internal and external environment, which can therefore be investigated through optical spectroscopy.[1,2] In order to study this influence in detail, we developed a hyperspectral IR fluorescence imaging setup based on a microscope with a liquid crystal tunable filter. By resolving the spectra of individual SWCNTs, and even along the length of SWCNTs, the effect of inhomogeneous broadening is largely eliminated, and spectral details can be resolved which are inaccessible in bulk spectroscopy. An automated image processing scheme is used to obtain statistics on large numbers of individual SWCNTs. In particular, we show that not only the spectral shift in emission between empty and water-filled[1] chirality sorted SWCNTs can be resolved, but even separate emission peaks are observed for the left- and right-handed enantiomers, which interact slightly differently with the chiral surfactant with which they are coated. The approach is particularly promising for the quantification of enantio-selective separation results. [1] W. Wenseleers et al., Adv. Mater. 19, 2274 (2007); S. Cambré and W. Wenseleers, Angew. Chem. 50, 2764 (2011); S. Cambré et al., ACS Nano 6, 2649 (2012). [2] J. Campo et al., ACS Nano 2021, 15, 2301−2317.

Single-wall carbon nanotubes (SWCNTs) possess unique electronic and optical properties, strongly depending on their exact chiral structure. Their quasi one-dimensional character results in the formation of strongly bound electron-hole pairs (excitons) that can even be observed at room temperature (i.e. binding energies of the order of several hundred meV).[1] The exciton fine structure of SWCNTs is quite complex, with multiple singlet and triplet excitonic states, of which only one is optically allowed, thereby resulting in extremely low fluorescence (PL) quantum yields. While the singlet excitons have already been investigated thoroughly, little is known about the longer-living triplet excitons. In this work, we report the characterization of triplet excitons in chirality-purified samples of (7,5) and (6,5) SWCNTs by means of optically detected magnetic resonance spectroscopy (ODMR), a technique that measures the influence on the emission of CNTs when making transitions between the spin levels of the triplet excitons. In both chiralities the nanotubes are shown to sustain two types of triplet exciton states, as shown by the symmetry and magnitude of their zero-field splitting parameters in the spin Hamiltonian, which are determined by careful fitting of magnetic-field orientation-dependent ODMR spectra of in-plane aligned SWCNTs. While the triplet excitons only weakly depend on the nanotube environment, an increase in zero-field splitting is found for (6,5) with respect to (7,5) nanotubes, in good agreement with the tighter confinement expected in the narrower-diameter nanotubes. [1] M.S. Dresselhaus et al, Ann. Rev. Phys. Chem. 2007, 58, 719 [2] D. Stich et al, Nature Photon. 2014 , 8,139; J. Palotás et al, ACS Nano 2020, 14, 11254

Specific and tunable modification to the opticalproperties of single-wall carbon nanotubes (SWCNTs) isdemonstrated through direct encapsulation into the nanotubeinterior of guest molecules with widely varying static dielectricconstants. Filled through simpleingestion of the guestmolecule, each SWCNT population is demonstrated to displaya robust modification to absorbance, fluorescence, and Ramanspectra. Over 30 distinct compounds, covering static dielectricconstants from 1.8 to 109, are inserted in large diameterSWCNTs (d = 1.104−1.524 nm) and more than 10 compoundsin small diameter SWCNTs (d = 0.747−1.153 nm), demonstratingthat the general effect of filler dielectric on thenanotube optical properties is a monotonic energy reduction(red-shifting) of the optical transitions with increased magnitude of the dielectric constant. Systematic fitting of the twodimensionalfluorescence−excitation and Raman spectra additionally enables determination of the critical filling diameter foreach molecule and distinguishing of overall trends from specific guest−host interactions. Comparisons to predictions fromexisting theory are presented, and specific guest molecule/SWCNT chirality combinations that disobey the general trend andtheory are identified. A general increase of the fluorescence intensity and line narrowing is observed for low dielectricconstants, with long linear alkane filled SWCNTs exhibiting emission intensities approaching those of empty SWCNTs. Theseresults demonstrate an exploitable modulation in the optical properties of SWCNTs and provide a foundation for examininghigher-order effects, such as due to nonbulk-like molecule stacking, in host−guest interactions in well-controlled nanoporesize materials.

Graphene nanoribbons with sub-nanometer widths are extremely interesting for nanoscale electronics and devices as they combine the unusual transport properties of graphene with the opening of a band gap due to quantum confinement in the lateral dimension. Strong research efforts are presently paid to grow such nanoribbons. Here we show the synthesis of 6- and 7-armchair graphene nanoribbons, with widths of 0.61 and 0.74 nm, and excitonic gaps of 1.83 and 2.18 eV, by high-temperature vacuum annealing of ferrocene molecules inside single-walled carbon nanotubes. The encapsulation of the so-obtained graphene nanoribbons is proved by atomic resolution electron microscopy, while their assignment is provided by a combination of an extensive wavelength-dependent Raman scattering characterization and quantum-chemical calculations. These findings enable a facile and scalable approach leading to the controlled growth and detailed analysis of well-defined sub-nanometer graphene nanoribbons., Comment: 35 pages, 4 figures

The hollow cores and well-defined diameters of single-walled carbon nanotubes (SWCNTs) allow for creation of one-dimensional hybrid structures by encapsulation of various molecules. Absorption and near-infrared photoluminescence-excitation (PLE) spectroscopy reveal that the absorption spectrum of encapsulated 1,3-bis[4-(dimethylamino)phenyl]-squaraine dye molecules inside SWCNTs is modulated by the SWCNT diameter, as observed through excitation energy transfer (EET) from the encapsulated molecules to the SWCNTs, implying a strongly diameter dependent stacking of the molecules inside the SWCNTs. Transient absorption spectroscopy, simultaneously probing the encapsulated dyes and the host SWCNTs, demonstrates this EET, which can be used as a route to diameter-dependent photosensitization, to be fast (sub-picosecond). A wide series of SWCNT samples is systematically characterized by absorption, PLE, and resonant Raman scattering (RRS), also identifying the critical diameter for squaraine filling. In addition, we find that SWCNT filling does not limit the selectivity of subsequent separation protocols (including polyfluorene polymers for isolating only semiconducting SWCNTs and aqueous two-phase separation for enrichment of specific SWCNT chiralities). The design of these functional hybrid systems, with tunable dye absorption, fast and efficient EET, and the ability to remove all metallic SWCNTs by subsequent separation, demonstrates potential for implementation in photoconversion devices.

We show that ultrasonication extracts inner tubes from double-wall carbon nanotubes (DWCNT), and characterize the process by density gradient ultracentrifugation (DGU) combined with in situ spectroscopic characterization in the density gradient. Our observations also cast new light on the question whether or not the inner tubes of DWCNTs fluoresce, which has been the subject of a long-standing debate, even though single‐DWCNT experiments have already shown drastic PL‐quenching for the inner CNT [1]. Indeed, in previous studies to characterise the PL from DWCNTs, they were typically solubilised using sonication, while here we see that upon sonication, the extraction of the inner tubes from the DWCNTs leads to much more, efficiently fluorescing SWCNTs. First, the DWCNTs were purified from SWCNTs and bundles using density gradient ultracentrifugation (DGU). Then, sonication is applied, after which the extracted inner tubes were separated from the DWCNTs by DGU and characterised by in situ resonant Raman and PL‐spectroscopy as a function of height in the centrifuge tube [2]. These subsequent in situ DGU experiments unambiguously prove the extraction of inner SWCNTs from DWCNTs, even by very brief sonication, and sonication-time-dependent measurements show that the process quickly saturates. [1] D. Levshov, R. Parret, H.-N. Tran, T. Michel, T.T. Cao, V.C. Nguyen, R. Arenal, V.N. Popov, S.B. Rochal, J.-L. Sauvajol, A.-A. Zahab, M. Paillet, Phys. Rev. B 96, 195410 (2017). [2] S. Cambré, P. Muyshondt, R. Federicci, W. Wenseleers, Nanoscale 7, 20015 (2015).

Single-wall carbon nanotubes (SWCNTs) possess unique electronic and optical properties that depend strongly on their exact chiral structure. Recent progress in the structure sorting of specific SWCNT chiralities, with increasing chiral purity[1], demands an effective characterization methodology to be developed to accurately determine the chiral composition of any SWCNT chirality. Very often, optical spectroscopy is used to assess the chiral composition of a sample, but absorption cross-sections, PL quantum efficiencies and Raman cross-sections are all depending on the exact chiral structure,[2] and can be strongly influenced by other factors such as the specific internal and external environment of the SWCNTs.[3] In this work, we systematically compare the chirality distribution obtained from 3 different optical spectroscopic techniques, i.e. absorption, wavelength-dependent Raman and fluorescence-excitation spectroscopy with the chirality distribution obtained from high-resolution transmission electron microscopy for both chirality-sorted and unsorted SWCNT samples. This combined approach demonstrates the importance of using a multi-technique characterization strategy for a reliable determination of SWCNT chirality distribution.[4] [1] J.A. Fagan, Nanoscale Adv. 1, 3307 (2019) and references therein [2] V.N. Popov, Nano Lett. 4, 1795 (2004) [3] S. Cambré et al, Angew. Chem. – Int Ed. 50, 2764 (2011); ACS nano 6, 2649 (2012) [4] A. Castan et al, Carbon 171, 968 (2021)

We show that ultrasonication readily extracts inner tubes from double-wall carbon nanotubes (DWCNT), and characterize the process by density gradient ultracentrifugation (DGU) combined with in situ spectroscopic characterization in the density gradient. Our observations also cast new light on the question whether or not the inner tubes of DWCNTs fluoresce, which has been the subject of a long-standing debate, even though single‐DWCNT experiments have already shown drastic PL‐quenching for the inner CNT [1]. Indeed, in previous studies to characterise the PL from DWCNTs, they were typically solubilised using sonication, while here we see that upon sonication, the extraction of the inner tubes from the DWCNTs leads to much more efficiently fluorescing SWCNTs. First, the DWCNTs were purified from SWCNTs and bundles using density gradient ultracentrifugation (DGU). Then, sonication is applied, after which the extracted inner tubes were separated from the DWCNTs by DGU and characterised by in situ resonant Raman and PL‐spectroscopy as a function of height in the centrifuge tube [2]. These subsequent in situ DGU experiments unambiguously prove the extraction of inner SWCNTs from DWCNTs, even by very brief sonication, and sonication-time-dependent measurements show that the process quickly saturates. [1] D. Levshov, R. Parret, H.-N. Tran, T. Michel, T.T. Cao, V.C. Nguyen, R. Arenal, V.N. Popov, S.B. Rochal, J.-L. Sauvajol, A.-A. Zahab, M. Paillet, Phys. Rev. B 96, 195410 (2017). [2] S. Cambré, P. Muyshondt, R. Federicci, W. Wenseleers, Nanoscale 7, 20015 (2015).

Three-stage pH-switchable organic second-order nonlinear optical (SO NLO) chromophores are synthesized and characterized by wavelengthdependent linear and nonlinear spectroscopy. The chromophores exhibit huge SO NLO responses in their ‘‘on’’ stages, and large switching contrasts between adjacent stages in both SO NLO response and fluorescence quantum yield, with moreover different ‘‘on/off’’ sequences for closely related compounds

Asymmetric dye molecules encapsulated inside single-walled carbon nanotubes align in a head-to-tail fashion to obtain a large cooperative nonlinear optical response. Asymmetric dye molecules have unusual optical and electronic properties1,2,3. For instance, they show a strong second-order nonlinear optical (NLO) response that has attracted great interest for potential applications in electro-optic modulators for optical telecommunications and in wavelength conversion of lasers2,3. However, the strong Coulombic interaction between the large dipole moments of these molecules favours a pairwise antiparallel alignment that cancels out the NLO response when incorporated into bulk materials. Here, we show that by including an elongated dipolar dye (p,p′-dimethylaminonitrostilbene, DANS, a prototypical asymmetric dye with a strong NLO response4) inside single-walled carbon nanotubes (SWCNTs)5,6, an ideal head-to-tail alignment in which all electric dipoles point in the same sense is naturally created. We have applied this concept to synthesize solution-processible DANS-filled SWCNTs that show an extremely large total dipole moment and static hyperpolarizability (β0 = 9,800 × 10−30 e.s.u.), resulting from the coherent alignment of arrays of ∼70 DANS molecules.

Ultra long linear carbon chains of more than 6000 carbon atoms have recently been synthesized within double-walled carbon nanotubes, and they show a promising new route to one--atom--wide semiconductors with a direct band gap. Theoretical studies predicted that this band gap can be tuned by the length of the chains, the end groups, and their interactions with the environment. However, different density functionals lead to very different values of the band gap of infinitely long carbyne. In this work, we applied resonant Raman excitation spectroscopy with more than 50 laser wavelengths to determine for the first time the band gap of long carbon chains encapsulated inside DWCNTs. The experimentally determined band gaps ranging from 2.253 to 1.848 eV follow a linear relation with Raman frequency. This lower bound is the smallest band gap of linear carbon chains observed so far. The comparison with experimental data obtained for short chains in gas phase or in solution demonstrates the effect of the DWCNT encapsulation, leading to an essential downshift of the band gap. This is explained by the interaction between the carbon chain and the host tube, which greatly modifies the chain's bond length alternation., Comment: 7 pages, 5 figures

The hollow core and well-defined diameters of carbon nanotubes (CNTs) make them the ideal template for ordering one-dimensional (1D) arrays of molecules and for the controlled synthesis of 1D carbon nanostructures from suitable precursor molecules. For instance, we previously demonstrated that in this way dipolar dye molecules can be naturally aligned in an ideal head-to-tail arrangement to create assemblies with a giant total nonlinear optical response,[1] and that the optical properties of dye molecules encapsulated in SWCNTs can be strongly modulated by the SWCNT diameter, indicating very specific diameter-dependent stacking and interactions of the molecules.[2] By thermal conversion also well-defined carbon structures such as long 1D carbon chains (carbyne) or graphene nanoribbons can be synthesized inside the hollow core of CNTs. Here we show that the structure and properties of such 1D carbon chains are strongly modulated by the interaction with the host tube, which greatly modifies the chains’ bond-length alternation.[3] We also show how the band-gap and electronic spectrum of the encapsulated carbon structures can be measured in detail, even in heterogeneous mixtures, through extensive wavelength dependent resonance Raman (excitation) spectroscopy, disentangling the vibrational and electronic spectra of the different structures. [1] S. Cambré, J. Campo et al., Nature Nanotechnol. 10, 248 (2015). [2] S. van Bezouw, D. H. Arias et al., ACS Nano 12, 6881 (2018). [3] L. Shi et al., Phys. Rev. Mater. 1, 075601 (2017).

The optical properties of single-wall carbon nanotubes (SWCNTs) are extremely sensitive to their external and internal environment. For example, filling the endohedral cavity with water molecules results in characteristic shifts and broadening of both the SWCNTs’ radial breathing mode vibrational frequency and their optical (electronic) transitions, as well as a quenching of their emission.[1] Although mostly ignored in literature, solvent ingestion effects are substantial, and can also be used to passivate the nanotube interior, by controlled manipulation of the endohedral environment prior to dispersion.[2] In this work, specific and tunable modification of the optical properties of SWCNTs is demonstrated through the direct encapsulation of guest molecules with widely varying dielectric constants. Over 30 different compounds with varying static dielectric constant have been encapsulated inside the SWCNTs and their spectroscopic analysis, in comparison to unfilled (empty) SWCNTs, demonstrates experimentally that the general effect of filler static dielectric constant on the SWCNTs’ optical properties corresponds to a monotonic energy reduction (red-shifting) of the optical transitions with increased magnitude for higher dielectric constants. In addition to these spectral shifts, the filling also reveals a general increase of fluorescence intensity with lower dielectric constants. Our investigation hence demonstrates a new degree of modulation of the SWCNTs’ optical properties by simple endohedral ingestion of various guest molecules. [1] S. Cambré et al. Phys. Rev. Lett. 104, 207401 (2010); W. Wenseleers et al. Adv. Mater. 19, 2274 (2007); S. Cambré et al. ACS Nano 6, 2649 (2012) [2] J. Campo et al Nanoscale Horizons 1, 317 (2016)

Molecules confined inside single-walled carbon nanotubes (SWCNTs) behave quite differently from their bulk analogues. In this Letter we present temperature-dependent (4.2 K up to room temperature) photoluminescence (PL) spectra of water-filled and empty single-chirality (6,5) SWCNTs. Superimposed on a linear temperature-dependent PL spectral shift of the empty SWCNTs, an additional stepwise PL spectral shift of the water-filled SWCNTs is observed at ∼150 K. With the empty SWCNTs serving as an ideal reference system, we assign this shift to temperature-induced changes occurring in the single-file chain of water molecules encapsulated in the tubes. Our molecular dynamics simulations further support the occurrence of a quasiphase transition of the orientational order of the water dipoles in the single-file chain.

A simple and quantitative, self-calibrating spectroscopic technique for the determination of the ratio of metallic to semiconducting single-wall carbon nanotubes (SWCNTs) in a bulk sample is presented. The technique is based on the measurement of the electron paramagnetic resonance (EPR) spectrum of the SWCNT sample to which cobalt(II)octaethylporphyrin (CoOEP) probe molecules have been added. This yields signals from both CoOEP molecules on metallic and on semiconducting tubes, which are easily distinguished and accurately characterized in this work. By applying this technique to a variety of SWCNT samples produced by different synthesis methods, it is shown that these signals for metallic and semiconducting tubes are independent of other factors such as tube length, defect density, and diameter, allowing the intensities of both signals for arbitrary samples to be retrieved by a straightforward least-squares regression. The technique is self-calibrating in that the EPR intensity can be directly related to the number of spins (number of CoOEP probe molecules), and as the adsorption of the CoOEP molecules is itself found to be unbiased toward metallic or semiconducting tubes, the measured intensities can be directly related to the mass percentage of metallic and semiconducting tubes in the bulk SWCNT sample. With the use of this method it was found that for some samples the metallic/semiconducting ratios strongly differed from the usual 1:2 ratio.

Aqueous two-phase (ATP) separation has been demonstrated as a fast, highly-scalable separation technique to sort single-wall carbon nanotubes (SWCNTs) by diameter, chirality, metallicity, etc.[1-2] In ATP, two water-soluble, yet immiscible polymers are mixed together at sufficiently high concentration after which they spontaneously form two phases with different hydrophilicity. In a typical separation protocol, SWCNTs are added to this two-polymer mixture with a combination of different surfactants, resulting in separation of different chiral species among both phases. While very promising separations have been achieved, the separation mechanism is not well understood In this paper, we present a series of ATP separations, in which surfactant combinations and concentrations are systematically varied. Absorption spectroscopy, multi-wavelength resonant Raman scattering and wavelength-dependent photoluminescence-excitation spectroscopy, combined with detailed two-dimensional spectral analysis, is applied to characterize the full composition of the resulting separated fractions and as such study the underlying separation mechanism. These systematic studies reveal that chirality-dependent surfactant interactions determine the separation order. [1]. C.Y. Khripin et al., J. Am. Chem. Soc. 2013, 135, 6822 [2]. N.K. Subbaiyan et al., ACS Nano 2014, 8, 1619

The hollow core and well-defined diameters of single-walled carbon nanotubes (SWCNTs) allow for creation of unique one-dimensional hybrid structures by encapsulation of various molecules. For instance, we previously demonstrated that in this way dipolar dye molecules can be naturally aligned in an ideal head-to-tail arrangement to create assemblies with a giant total nonlinear optical response.[1] Here, we show that the optical properties of dye molecules encapsulated in SWCNTs can be strongly modulated by the SWCNT diameter, indicating very specific diameter-dependent stacking and interactions of the molecules. The filling is thoroughly characterized by optical absorption, resonant Raman, and two-dimensional infrared photoluminescence excitation (PLE) spectroscopy. Energy transfer probed by PLE spectroscopy shows the absorption spectrum of the dyes to be strongly diameter-dependent, and transient absorption spectroscopy, simultaneously probing the encapsulated dyes and the host SWCNTs, demonstrates sub-picosecond EET from encapsulated molecules to the host SWCNTs. The design of these functional hybrid systems, with tuneable dye absorption, EET depending on the SWCNT diameter and the ability to remove all metallic SWCNTs by subsequent separation, demonstrates potential for implementation in dedicated photo-conversion devices. [1] S. Cambré, J. Campo et al., Nature Nanotechnol. 10, 248 (2015).

A simple one-pot method produces silver nanoparticles coated with aryl thiols that show intense, broad nonplasmonic optical properties. The synthesis works with many aryl-thiol capping ligands, including water-soluble 4-mercaptobenzoic acid. The nanoparticles produced show linear absorption that is broader, stronger, and more structured than most conventional organic and inorganic dyes.

The encapsulation of an organometallic paramagnetic molecule, copper(II) acetylacetonate (Cu(acac)2), inside single-walled carbon nanotubes (SW CNTs) is studied using continuous wave electron paramagnetic resonance (EPR). By preparing samples from fully opened as well as from closed SW CNTs, the EPR spectra of encapsulated and nonencapsulated molecules can be clearly identified. The EPR spectrum originating from the encapsulated molecules is unchanged by dispersion of the endohedral nanohybrids in a solvent or by solubilization of the nanohybrids in water using bile salt surfactants, demonstrating that the CNTs protect them from changes in their external environment. The EPR parameters obtained for the encapsulated molecules show that they experience an extremely apolar environment. From the dipolar broadening of the EPR lines of the nanohybrids, the distances between the encapsulated molecules inside the CNTs can be estimated by adapting Van Vlecks method of moments for the case of a one-dimensional array of molecules. Furthermore, a combination of orientation dependent EPR experiments and polarized Raman scattering on preferentially aligned CNT hybrids in stretched polymer film samples yields information on the orientational distribution of the encapsulated molecules inside the SW CNTs.

A new family of three-legged piano stool structured organometallic compounds containing the ¦Ç5-cyclopentadienylruthenium(II)/iron(II) fragments {M(¦Ç5-C5H5) (DPPE)}+, {Ru(¦Ç5-C5H5)(PPh3)2}+ and {Ru(¦Ç5-C5H5)(TMEDA)}+ with coordinated thiophene based chromophores, namely 5-(2-thiophen-2-yl-vinyl)-thiophene-2-carbonitrile (L1) and 5-[2-(5-Nitro-thiophen-2-yl)-vinyl]-thiophene-2-carbonitrile (L2) has been synthesized and fully characterized by 1H, 13C, 31P NMR, IR and UV¨CVis spectroscopies. Also, electrochemical studies were carried out by cyclic voltammetry and all experimental data are interpreted and compared with related compounds under the scope of NLO properties. Compounds [Ru(¦Ç5-C5H5)(DPPE)(NC(C4H2S)C(H)C(H)(C4H3S))][CF3SO3] (1¡äRu) [Fe(¦Ç5-C5H5)(DPPE)(NC(C4H2S)C(H)C(H)(C4H3S))] [PF6] (1Fe) and [Ru(¦Ç5-C5H5)(DPPE)(NC(C4H2S)C(H)C(H)(C4H2S)NO2)][CF3SO3] (4¡äRu) were also crystallographically characterized.

Insertion of various compounds into single-walled carbon nanotubes (SWCNTs) is a challenging approach for the design of one-dimensional nanostructures with novel functionalities. It has already been shown that fullerenes as well as other organic and inorganic compounds can be introduced in SWCNTs. [1] Molecular dynamics simulations have suggested that water can also enter the SWCNTs despite the hydrophobic nature of the CNT wall, and that even very fast transport can take place. [2] Very recently, remarkably efficient water transport through nanotube membranes was observed, [3] and also the use of water-filled CNTs as nanovalves to control gas flow inside CNTs was demonstrated. [4] Monitoring and optimization of the accessibility of the nanotubes are of prime importance in these different applications. In spite of the many reports concerning the opening/filling of CNTs, a quantitative evaluation of the tube opening for the different processes is still not available. SWCNT opening has been shown to occur as a side effect in various acid-based purification methods and has been intensively studied with electron microscopy. [5] A series of experimental studies including nuclear magnetic resonance (NMR), [6] X-ray diffraction (XRD), [7] IR spectroscopy, [8] and neutron scattering, [9] have demonstrated that water can enter SWCNTs, by probing the encapsulation induced changes in the water. Raman scattering of H2O vibrations and the tangential modes of CNTs indicate adsorption/desorption of water on CNTs, however no quantitative information on the CNTs could be obtained. [10] Very recently, Longhurst and Quirke [11] calculated that filling of CNTs with water would lead to an upshift of the radial breathing mode (RBM) of the CNTs by 2–6 cm –1 . Here, we show that the RBM resonant Raman features of empty and water-filled SWCNTs can be very well resolved, even in measurements on bulk solutions, provided the nanotubes are solubilized using bile salt surfactants. [12] Furthermore, the vibrational and electronic shifts and damping upon filling are accurately determined for a series of SWCNTs. With this knowledge we show that resonant Raman spectroscopy can be used as a quantitative ratiometric technique to monitor the opening and closing of CNTs under different treatments. The electronic properties of CNTs depend critically on their structure, [13] which is uniquely defined by the chiral indices (n,m). Resonance Raman scattering (RRS) is a powerful technique to study CNTs, because the RBM frequency (xvib )o f the CNTs is directly related to the diameter of the tube: xvib= c1/D+c2, where D is the nanotube diameter. Different values for the constants have been reported, among which c1=223.5 nmcm –1 and c2=12.5 cm –1 are the most commonly used. [14] RRS was applied to bundles or individual nanotubes

We hereby report on the design of a set-up combining micro-resonance Raman and absorption spectroscopy with a microfluidic system. The set-up enabled us to study the nerve globin of Aphrodite aculeata in the functional isolated nerve cord under varying physiological conditions for extended periods of time. The oxygenation cycle of the organism was triggered by utilizing the microfluidic system that allowed for a fast switch between aerobic and anaerobic conditions. The nerve globin was found to very easily shift from a penta-coordinated high spin ferrous form to the oxy state upon a change from anaerobic to aerobic conditions. The observed fast reaction to varying O2 concentrations supports an oxygencarrying and/or -storing function of the nerve globin. In addition, by combining resonance Raman and absorption spectroscopy, the physiological response could be distinguished from light-induced effects. © 2007 Elsevier B.V. All rights reserved.

Density gradient ultracentrifugation (DGU) becomes increasingly important for the sorting of nanomaterials according to the particles' density, hence structure and dimensions, which determine their unique properties, but the further development of this separation technique is hindered by the limited precision with which the densities could be characterized. In this work, we determine these densities by position-dependent 2D wavelength-dependent IR fluorescence-excitation and resonant Raman spectroscopy measured directly in the density gradient after ultracentrifugation. We apply this method to study the diameter and chirality-dependent sorting of empty and water-filled single-walled carbon nanotubes coated with two different surfactants, sodium cholate (SC) and sodium deoxycholate (DOC). The results elucidate the long standing contradiction that SC would provide better diameter sorting, while DOC is the most efficient surfactant to solubilise the nanotubes. A more predictable separation is obtained for empty DOC-coated nanotubes since their density is found to vary very smoothly with diameter. The accurate and chirality-dependent densities furthermore provide information on the surfactant coating, which is also important for other separation techniques, and allow to determine the mass percentage of water encapsulated inside the nanotubes.

A practical yet accurate dispersion model for the molecular first hyperpolarizability beta is presented, incorporating both homogeneous and inhomogeneous line broadening because these affect the beta dispersion differently, even if they are indistinguishable in linear absorption. Consequently, combining the absorption spectrum with one free shape-determining parameter G(inhom), the inhomogeneous line width, turns out to be. necessary and sufficient to obtain a reliable description of the beta dispersion, requiring no information on the homogeneous (including vibronic) and inhomogeneous line broadening mechanisms involved, providing an ideal model for practical use in extrapolating experimental nonlinear optical (NLO) data. The model is applied to the efficient NLO chromophore picolinium quinodimethane, yielding an excellent fit of the two photon resonant wavelength dependent data and a dependable static, value beta(0) = 316 x 10(-30) esu. Furthermore, we show that including a second electronic excited state in the model does yield an improved description of the NLO data at shorter wavelengths but has only limited influence on beta(0).

A series of pi-conjugated styryl quinolinium push-pull chromophores have been designed and synthesized in order to examine the electron-withdrawing strength of various quinolinium electron acceptor groups, and their influence on the photophysical properties and in particular on the second-order nonlinear optical response. The static molecular first hyperpolarizabilities measured by long-wavelength hyper-Rayleigh scattering are found to follow the order of the electron withdrawing strength of their acceptor groups as determined by NMR analysis. The quinolinium chromophores based on the strongest electron acceptor groups (1,2- and 1,4-dimethylquinolinium) exhibit remarkably large first hyperpolarizability values of 233 and 256 x 10(-30) esu respectively, which is higher than that of the well-known and widely-used pyridinium analogue 4-(4-(dimethylamino)styryl)-1-methylpyridinium 4-methylbenzenesulfonate with first hyperpolarizability = 183 x 10(-30) esu. The dimethylquinolinium electron acceptor groups exhibit increased electron-withdrawing strength compared to the dimethylpyridinium group used in 4-(4-(dimethylamino) styryl)-1-methylpyridinium 4-methylbenzenesulfonate, and therefore have a high potential for photonic applications. (C) 2014 Elsevier Ltd. All rights reserved.

Measurements of the nonlinear optical (NLO) response (molecular first hyperpolarizability, beta) of two pH-switchable dyes were performed by means of hyper-Rayleigh scattering (HRS) over a wide range of laser wavelengths and pH values. The extensive wavelength-dependent NLO data combined with linear optical spectroscopy allow the results to be related to the electronic structures of the push-pull systems and the NLO switching contrast to be optimized. The results are modeled theoretically using a vibronic beta dispersion model including both homogeneous and inhomogeneous broadening, yielding a full wavelength dependence of beta, as well as of its switching contrast. The hyperpolarizabilities measured for the basic "on"-states are the highest ever reported for such compounds, reaching over 200 X 10(-30) esu in the static limit and over 2700 X 10(-30) esu at resonance. By combining a high intrinsic contrast in the static hyperpolarizability beta(0) with a large shift in resonance, an extremely large range in contrasts of the HRS signal is reached of more than 2 orders of magnitude at wavelengths accessible with the widely used Ti:sapphire laser and moreover within a biologically compatible pH range.

The mechanical stability of single-wall carbon nanotubes (SWCNTs) at high pressure was studied by high-resolution resonant Raman and wavelength-dependent fluorescence-excitation (PLE) spectroscopy resolving the vibrational and electronic resonances of 18 individual chiralities and furthermore even resolving the different behaviour of empty (closed, pristine) and water-filled (opened) SWCNTs (diameter range = 0.61.42 nm). We find that water-filling exerts a stabilizing counter-pressure on the SWCNT walls, leading to an increasing difference between the radial breathing mode frequencies of water-filled and empty SWCNTs at elevated pressures. For small diameter SWCNTs (d < 1 nm) with a chiral angle of ∼12°, in particular for the (7,2) chirality, an anomalous behaviour is observed, revealing an increased mechanical instability for these SWCNTs. We furthermore ascribe the longstanding contradiction between experiments and theory on the collapse pressure of SWCNTs to the presence of filling in most experiments to date, while empty SWCNTs follow the theoretically predicted collapse behaviour.

A series of ionic pseudo-octahedral trans-hydrido(nitrile)iron(II) complexes with the general formula [Fe(H)(dppe)2(4NCR)][PF6] [dppe = 1,2-bis(diphenylphosphanyl)ethane; R = acceptor-substituted conjugated ligand] have been synthesised by chloride abstraction from the starting compound trans-[FeHCl(dppe)2] and fully characterised. First hyperpolarisabilities (β) have been determined by hyper-Rayleigh scattering (HRS) at the fundamental wavelength of 1072 nm and the high near-resonant values obtained (up to 1130 × 10 – 30 esu) are interpreted in terms of the two-level model (TLM) and are correlated with IR and NMR spectroscopic data. Wavelength-dependent HRS has been performed in the

We have investigated a wide variety of surfactants for their efficiency in dissolving isolated single-walled carbon nanotubes (SWNTs) in water. In doing so, we have completely avoided the harsh chemical or mechanical conditions, such as acid or ultrasonic treatments, that are known to damage SWNTs. Bile salts in particular are found to be exceptionally effective in dissolving individual tubes, as evidenced by highly resolved optical absorption spectra, bright bandgap fluorescence, and the unprecedented resolution (∼ 2.5 cm - 1 ) of the radial breathing modes in Raman spectra. This is attributed to the formation of very regular and stable micelles around the nanotubes providing an unusually homogeneous environment. Quantitative information concerning the degree of solubilization is obtained from absorption spectroscopy.

SummaryandConclusions Wehavestudiedthetwo-photonabsorptionpropertiesoftwoacceptor-p-acceptor systems with dioxaborine acceptor unitsusing highly correlated quantum-mechanical simulations, andfoundexcellentagreementwithnanosecondandfemtosecondspectroscopicdata.Intheaccessiblespectralregion,therearetwo significant TPA features. The calculations show that thelarge difference in the nonlinear absorption response of thetwo states involved is a consequence of correlation-inducedoscillatorstrengthredistribution;thisemphasizesthatelectroncorrelation is the key to understanding the factors governingtheTPAresponseinp-conjugatedorganicchromophores.Con-figuration mixing also affects the lowest one-photon excitedstate and, in this way, reduces the overall TPA response thatcanbeachieved.Moreover,wefindstrongindicationsthatTPAintotheone-photonallowedstate(S 1 )ismediatedbychannelsinvolving vibrational sublevels of the ground state, therebysupportingthetheoreticalpredictionsinref.[18] Methodology Detailsregardingthesynthesisofthecompoundsandtheirspec-troscopic investigations are contained in the Supporting Informa-tion.Thespecificvaluesofthefluorescencequantumyieldsdeter-minedforIandIIare68and72%,respectively.Quantum-Chemical Modeling: To calculate the TPA cross-sections,westartfrommoleculargeometriesoptimizedwiththesemiempir-icalAM1Hamiltonian.

The molecular first hyperpolarizability, β, and the X-ray crystal structure of the complex [Fe(η5-C5H5)((R)–PROPHOS)(p-NCC6H4NO2)][PF6] ((R)–PROPHOS=(R)–(+)-bis-(1,2-diphenylphosphino)propane) were determined. A near-resonant enhanced β value as high as 545×10−30 esu was obtained from hyper-Rayleigh scattering measurements. In addition, the compound crystallizes in the space group P1 with a perfect alignment of the dipolar molecules (only a single chromophore per unit cell), thus maximizing the macroscopic nonlinearity for electro-optic or parametric frequency conversion applications. The molecular packing in the crystal is analyzed in order to understand the factors leading to the perfect alignment.

A photoresponsive polymeric hydrogel cantilever that deflects under illumination has been fabricated by using two-photon three-dimensional lithography. The hydrogel was prepared from a comonomer solution containing acryloylacetone, acrylamide, and N,N′-methylene bisacrylamide. The photoresponse of the cantilever was activated by photoexcitation of acetylacetone groups at 244 nm. Deflection of the cantilever by ∼ 45° was effected upon UV irradiation for 20 min.

A comparative study of the two-photon absorption (TPA) properties of octupolar compounds and their dipolar one-dimensional counterparts is presented on the basis of correlated quantum-chemical calculations. The roles of dimensionality and symmetry are first discussed on the basis of a simple exciton picture where the ground-state and excited-state wavefunctions of three-arm octupolar systems are built from a linear combination of the corresponding single-arm wavefunctions. This model predicts a factor of 3 increase in the TPA cross section in the limiting case of three independent charge-transfer pathways. When taking into account the full chemical structures of representative octupolar molecules, the results of the calculations indicate that a much larger enhancement associated with an increase in dimensionality and delocalization can be achieved when the core of the chromophore allows significant electronic coupling among the individual arms. These theoretical predictions are in agreement with the experimental determination of the TPA cross sections for crystal violet and the related compound, brilliant green, and suggest new strategies for the design of conjugated materials with large TPA cross sections.

A series of new acetylide complexes of the type [Fe(η5-C5H5)(P⌒P)(p-C⋮CC6H4R)] (P⌒P = DPPE (=1,2-bis(diphenylphosphino)ethane), (R)-PROPHOS (=(R)-(+)-1,2-bis(diphenylphosphino)propane), R = NO2, C6...

Specific and tunable modification to the optical properties of single-wall carbon nanotubes is demonstrated through the direct encapsulation into the nanotube interior of guest molecules with measured static dielectric constants. Optical measurements on SWCNT populations containing over thirty distinct simple compounds of varying static dielectric from 1.8 to 109 in large diameter nanotubes, and 15 compounds in small diameter nanotubes demonstrate for the first time experimentally the general effect of filler static dielectric on the nanotube optical properties. Comparison to effective medium theory predictions is presented, and guest molecules are identified that lead to effects disobeying the general trend and theory. These results both demonstrate a new degree of exploitable modulation in the optical properties of SWCNTs, and provide a foundation for examining higher order effects in host-guest interactions in well controlled pore size materials.

Tremendous progress and innovation has ushered the incorporation of semiconducting single-walled carbon nanotubes (s-SWCNTs) as active components into organic/inorganic/hybrid solar cells and thermoelectrics. For solar photoconversion, strong and tunable absorption is necessitated, suggesting that s-SWCNTs can play a role as light-harvesting components, however the narrow and distinct excitonic optical transitions found in s-SWCNT systems limit broad-band absorption. As such, we introduce encapsulation of small molecules within the endohedral volume of s-SWCNTs as a route to increase and extend light absorption in regions outside s-SWCNT excitonic transitions. Creation of this self-assembled supra-molecular system can strongly modify the opto-electronic properties of both the s-SWCNT and encapsulated molecule. We investigate excitation energy transfer occurring from encapsulated dye molecules to s-SWCNTs, which results in luminescent SWCNT excitons. We exploit the high-throughput and chiral selectivity of polyfluorene wrapping methods to generate dispersions of s-SWCNTs with dye encapsulation. We demonstrate that the selectivity of the polyfluorene polymer for semiconducting chiral distributions is not affected by the presence of encapsulated molecules. Tracking the excited state transient absorption signatures of excitation energy transfer provides detailed information regarding dynamics of both the encapsulated dye and s-SWCNTs. We observe sub-picosecond excitation energy transfer of excitons generated in dye molecules to the surrounding s-SWCNTs. Photoluminescence excitation maps reveal that the absorption of encapsulated dye molecules depends sensitively on the diameter of the s-SWCNT in which they are encapsulated. We consider a simple molecular exciton model to describe aggregate formation within the s-SWCNT endohedral volume, which reveals that the dye molecules adopt unique aggregate structures that are defined both by a competition between intermolecular interactions between the dye molecules and confinement effects due to the s-SWCNT diameter. Small molecule encapsulation in s-SWCNTs serves as a strong platform to control intermolecular interactions in small molecule systems through confinement, which opens up the possibility of enhancing photo-induced extraction of energy and charge in s-SWCNTs solar photoconversion systems.

The confinement of water molecules in one-dimensional channels leads to fascinating new properties which are of critical importance for many processes in biology, geology, catalysis and nanofluidics. Single-walled carbon nanotubes (SWCNTs) are one of the most promising model systems to investigate molecules under confinement. They combined atomically-precise diameters that deliver the necessary level of confinement with a weak interaction of the water molecules with their smooth inner walls. Despite significant efforts, theoretical predictions of the behavior and peculiar properties of a single-file chain of water water molecules (e.g. interesting for ultrafast proton transport) have proven to be very hard to validate experimentally. In this work, we present temperature-dependent (4.2K up to room temperature) photoluminescence (PL) spectra of water-filled and empty chirality-sorted (6,5) SWCNTs. Superimposed on a linear temperature-depenent PL spectral shift of the empty tubes, an additional stepwise PL shift of the water-filled SWCNTs is observed at around 150K. With the empty SWCNTs serving as the ideal reference system, we can assign this observation to temperature-induced changes occuring within the single file molecular chain. Supported by new Molecular Dynamics simulations, we obtain the first experimental evidence of a quasi phase transition of the orientation of the molecular dipoles within such a one-dimensional single file chain of water molecules.

New complexes of the type [FeCp(P_P)(p-NCR)][PF6] (P_P=(S)-PROLOPHOS, DPPE and (R)-PROPHOS ((S)-PROLOPHOS=(S)-N-(diphenylphosphino)-2-diphenylphosphinooxymethylpyrrolidine; DPPE=1,2-bis(diphenylphosphino)ethane; (R)-PROPHOS=(R)-(+)-1,2-bis(diphenylphosphino)propane); R=C6H4N(CH3)2, C6H4NO2, (E)-C(H)C(H)C6H4NO2, C6H4C6H4NO2) have been synthesized and characterized. Spectroscopic data were evaluated in order to correlate the tuning of the electronic density at the metal center with the first molecular hyperpolarizabilities (β) determined by hyper-Rayleigh scattering at 1064 nm. Experimental β values increase with chain length and with the enhancement of the donor ability of the bidentate phosphine. [FeCp(DPPE)((E)-p-NCC(H)C(H)C6H4NO2)][PF6] is found to have the highest β value (570×10−30 esu) in the series. Molecular orbital calculations were carried out to understand the geometric and electronic factors involved and also to compute the static hyperpolarizabilities, β0. These results are consistent with the trend observed in the β0 values derived from experiment on the basis of the two-level model. The complex [FeCp(DPPE)(p-NCC6H4NO2)][PF6] was crystallographically characterized. The compound crystallizes in the centrosymmetric space group Pbcn. Bond distances within the nitrile ligand were discussed in order to evaluate the extension of π-backdonation suggested by spectroscopic data.

A new family of organometallic Ni(II) benzonitrile derivatives bearing strong donor substituents of general formula [Ni(η5-C5H5){P(C6H5)3}NCC6H4R][PF6] (R=NH2, N(CH3)2, C6H5, OCH3, H, F) has been synthesized. A structural study by X-ray diffraction of the compound with R=NH2 showed crystallization on the centrosymmetric monoclinic space group, P21/n, with a quasi planar structure of the coordinated nitrile. First and second hyperpolarizabilities evaluated by hyper-Rayleigh scattering and Maker fringe techniques showed essentially the same values for the complexes and the uncoordinated chromophores. Theoretical studies by the extended Huckel method found a small amount of π delocalization due to the cancelling effects on the interaction of the metal fragment orbitals with π and π* nitrile orbitals.

The synthesis strategy for the preparation of novel platinum acetylide homometallic and heterobimetallic dendrimers (containing Fe as the other metal fragment) based on a 2,4,6-tris(4-ethynyl)phenyl-1,3,5-triazine core (3) is reported. All the dendrimer generations (G0G2) were synthesized under copper-free conditions following a divergent route. The G0-Pt dendrimer (4) was synthesized using the 1,3,5-triazine core (3) and cis-[Pt(PEt3)2Cl2] with a molar ratio of 1/4. The advantage of the current method is that different dendrimers can be prepared by following the same procedure with only changes in the molar ratios of the reactants involved. For instance, when 3 reacts with 4 in a 4/1 molar ratio, the G1 dendrimer 7 is afforded without the peripheral Pt moiety, but the G1 dendrimer with the peripheral Pt moiety (8) is formed when 3 reacts with 4 in a 1/3 molar ratio. On the other hand, the G2 dendrimer with a peripheral Pt moiety (9) is synthesized when 7 reacts with 4 in a 1/6 molar ratio. The heterobimetallic dendrimers were synthesized up to generation 1 by capping the corresponding Pt dendrimers with the ethynylferrocenyl group (EFC). The respective G0 (6)- and G1-capped (10) dendrimers were synthesized when EFC reacted with 4 and 8 in molar ratios of 9/1 and 18/1, respectively. Nonlinear optical (NLO) polarizabilities measured by hyper-Rayleigh scattering (HRS) have been evaluated for the core 3, for the G0 dendrimer 4, and for the G0 dendrimer capped with EFC (6). In spite of the fact that the stability of the higher generations in chloroform is too low to allow HRS measurements, the reported NLO results show a remarkable enhancement (plus 50%) upon capping the zero dendrimer generation (6), reflecting the importance of the introduction of electron donor organometallic capping groups in the hyperpolarizabilities of the resulting dendrimers.

The discovery that natural bile salt surfactants are extraordinarily efficient at solubilizing individual, intact single-wall carbon nanotubes (SWCNTs) in water[1], soon enabled the separation of different SWCNT structures for the first time by density gradient ultracentrifugation (DGU),[2] and more recently also by aqueous two-phase extraction (ATP).[3,4] Despite very nice results for a limited number of small diameter SWCNT chiralities that have been isolated as individual species by DGU and ATP, the underlying mechanisms are not fully understood and the number of variables to be explored and optimized is enormous, preventing a systematic extension to other chiralities. Based on the unique capabilities of optical spectroscopy for characterizing SWCNTs, we present a systematic study of the structure sorting of DGU and ATP. We combine a direct in situ optical characterization of the centrifuge tubes after DGU[5] with systematic concentration-dependent ATP separations for different (mixed) surfactants and as such obtain a more detailed understanding of and control over both separation mechanisms. These systematic studies reveal that chirality-dependent surfactant interactions determine the separation order. [1] W. Wenseleers et al., Adv. Fucnt. Mater. 2004, 14, 1105 [2]. M.S. Arnold et al., Nature Nanotechnol. 2006, 1, 60 [3]. C.Y. Khripin et al., J. Am. Chem. Soc. 2013, 135, 6822 [4]. N.K. Subbaiyan et al., ACS Nano 2014, 8, 1619 [5]. S. Cambré et al., Nanoscale 2015 , 7, 20015

International audience; The influence of water-filling on the photoluminescence (PL) properties of SWCNTs is studied by ensemble and single-molecule PL spectroscopy. Red-shifted PL and PL excitation spectra are observed upon water filling for 16 chiralities and can be used to unambiguously distinguish empty SWCNTs from filled ones. The effect of water-filling on the optical transitions is well reproduced by a continuum dielectric constant model previously developed to describe the influence of the nanotube outer environment. Empty nanotubes display narrower luminescence lines and lower inhomogeneous broadening, signatures of reduced extrinsic perturbations. The radial breathing mode (RBM) phonon side band is clearly observed in the PL spectrum of small diameter empty tubes and a strong exciton-phonon coupling is measured for this vibration. Biexponential PL decays are observed for empty and water filled tubes, and only the short living component is influenced by the water-filling. This may be attributed to a shortening of the radiative lifetime of the bright state by the inner dielectric environment.