Ever since the discovery of carbon nanotubes (CNTs), many groups have endeavored to understand the fundamental properties of the CNTs. The redox properties (i.e. electronic densities, the Fermi levels, redox potentials) of single-walled carbon nanotubes (SWNTs) are related to the structures of SWNTs that have a specified diameter and chirality angle uniquely related to a pair of integers (n,m); the so-called chiral indices. [1,2] Many attempts have been made to determine the electronic properties of SWNTs using scanning tunneling spectroscopy, [3] redox titrimetry, [4] photoluminescence (PL) measurements, [5][6][7] and spectroelectrochemistry; [8][9][10][11][12][13] however, the success in the determination of the redox properties as already reported has been low. Recently, Paolucci et al. [12] employed Vis-near-IR absorption spectroelectrochemistry to estimate the redox potentials of the SWNTs dissolved in an ultradry dimethylsulfoxide (DMSO) solution; however, it is not easy to determine the redox potentials of isolated (n,m)SWNTs using this method because SWNTs with several different chiral indices have band gaps in the near-IR region that overlap one another. We now describe a simple method for the determination of the redox potentials of many (in this study, fifteen) individual (n,m)SWNTs using near-IR PL spectroelectrochemistry in an aqueous medium.Strategic approaches toward the solubilization of CNTs are essential for many applications of CNTs [14] and numerous dispersants including carboxymethylcellulose sodium salt (CMC, Figure S1a in the Supporting Information) [15] have been used to individually dissolve SWNTs. In this study, we fabricated a non-fluorescent transparent indium tin oxide (ITO) electrode modified with a cast film of CMC/poly-(diallyldimethylammonium chloride) (PDDA; Figure S1b in the Supporting Information) that contained isolated SWNTs (for details, see Experimental Section in the Supporting Information).We have discovered that we can determine the redox potentials of isolated SWNTs having their own chirality indices by in situ near-IR PL spectroelectrochemistry at the fabricated modified ITO electrode. This modified film retains the isolated SWNTs and the spectroelectrochemical results are analyzed with the Nernst equation.Externally applied potentials were changed in the range of ) and oxidized form (SWNT n+ ) when the external potential was applied to the electrode in arbitrary steps from 0.0 V to À1.0 V and from 0.0 V to + 1.1 V, respectively. After each potential step, the applied potential was returned to 0.0 V and it was confirmed that no significant spectral change in the SWNT had occurred, namely, the SWNTs in the film are stable during these electrochemically driven redox processes. This behavior of the SWNTs is consistent with those in Visnear-IR absorption [8b] and Raman [10b] spectroelectrochemical studies.We carried out in situ near-IR absorption spectroelectrochemistry using the modified electrode. The near-IR absorption spectra of the individually solubilized SWNTs wer...

Understanding of electronic and optical features of single-walled carbon nanotubes (SWNTs) has been a central issue in science and nanotechnology of carbon nanotubes. We describe the detection of both the positive trion (positively charged exciton) and negative trion (negatively charged exciton) as a three-particle bound state in the SWNTs at room temperature by an in situ photoluminescence spectroelectrochemistry method for an isolated SWNT film cast on an ITO electrode. The electrochemical hole and electron dopings enable us to detect such trions on the SWNTs. The large energy difference between the singlet bright exciton and the negative and positive trions showing a tube diameter dependence is determined by both the exchange splitting energy and the trion binding energy. In contrast to conventional compound semiconductors, on the SWNTs, the negative trion has almost the same binding energy to the positive trion, which is attributed to nearly identical effective masses of the holes and electrons.

The electronic states of carbon nanotubes are one of the most fundamental properties of the nanotubes. We now describe the finding that the band gaps of (n,m)SWNTs are strongly affected by the change in microdielectric environments around the isolated nanotubes. In situ photoluminescence (PL) spectroelectrochemistry of the films containing 15 isolated (n,m)single-walled carbon nanotubes (SWNTs) cast on ITO electrodes in organic solvents including DMSO, acetonitirile, DMF, THF, and chloroform was completed and then the oxidation and reduction potentials, and band gaps (ΔE(electr)) of the (n,m)SWNTs in the solvents were determined. We have discovered that the ΔE(electr) of the (n,m)SWNTs become greater as the solvent dielectric constants decreased, which is in sharp contrast to the optical band gaps (ΔE(opt)) that show virtually no solvent dependence. Such a strong solvent dependence of the electrochemical band gaps is due to the difference in the solvation energy of the charged SWNTs produced during the electrochemical processes. The ΔE(electr) of both mod types of the SWNTs, mod = 1 and mod = 2, linearly increased versus the reciprocal of the tube diameter, which agrees with the theory. Moreover, the states of the π-electrons in the SWNTs were evaluated from the dependence of the band gaps on the diameter of the SWNTs. Furthermore, the states of the π-electrons on the sidewalls of the SWNTs were evaluated using the γ(0) values, a parameter representing the measure of the stability or the degree of delocalization of π-electrons in the sidewall of the SWNTs, and revealed that the γ(0) values of the mod = 1 and mod = 2 SWNTs increased with a decrease in the dielectric constants of the solvents in the range of 38-79. This study has enabled us to understand the essential electronic properties of the carbon nanotubes.

Ever since the discovery of carbon nanotubes (CNTs), many groups have endeavored to understand the fundamental properties of the CNTs. The redox properties (i.e. electronic densities, the Fermi levels, redox potentials) of single-walled carbon nanotubes (SWNTs) are related to the structures of SWNTs that have a specified diameter and chirality angle uniquely related to a pair of integers (n,m); the so-called chiral indices. [1,2] Many attempts have been made to determine the electronic properties of SWNTs using scanning tunneling spectroscopy, [3] redox titrimetry, [4] photoluminescence (PL) measurements, [5][6][7] and spectroelectrochemistry; [8][9][10][11][12][13] however, the success in the determination of the redox properties as already reported has been low. Recently, Paolucci et al. [12] employed Vis-near-IR absorption spectroelectrochemistry to estimate the redox potentials of the SWNTs dissolved in an ultradry dimethylsulfoxide (DMSO) solution; however, it is not easy to determine the redox potentials of isolated (n,m)SWNTs using this method because SWNTs with several different chiral indices have band gaps in the near-IR region that overlap one another. We now describe a simple method for the determination of the redox potentials of many (in this study, fifteen) individual (n,m)SWNTs using near-IR PL spectroelectrochemistry in an aqueous medium.Strategic approaches toward the solubilization of CNTs are essential for many applications of CNTs [14] and numerous dispersants including carboxymethylcellulose sodium salt (CMC, Figure S1a in the Supporting Information) [15] have been used to individually dissolve SWNTs. In this study, we fabricated a non-fluorescent transparent indium tin oxide (ITO) electrode modified with a cast film of CMC/poly-(diallyldimethylammonium chloride) (PDDA; Figure S1b in the Supporting Information) that contained isolated SWNTs (for details, see Experimental Section in the Supporting Information).We have discovered that we can determine the redox potentials of isolated SWNTs having their own chirality indices by in situ near-IR PL spectroelectrochemistry at the fabricated modified ITO electrode. This modified film retains the isolated SWNTs and the spectroelectrochemical results are analyzed with the Nernst equation.Externally applied potentials were changed in the range of À1.0-+ 1.1 V versus Ag j AgCl (saturated KCl) in 0.3 m aqueous NaCl containing 30 mm Na 2 HPO 4 (pH 8) because in this potential range, both CMC and PDDA are electroinactive. The open circuit potential (OCP) of the modified electrode was around 0.0 V, which is almost identical with the OCP value [8b] of a bundled SWNT film on an electrode. Herein, neutral SWNTs are denoted as SWNT 0 . The SWNT 0 were changed into reduced form (denoted as SWNT nÀ ) and oxidized form (SWNT n+ ) when the external potential was applied to the electrode in arbitrary steps from 0.0 V to À1.0 V and from 0.0 V to + 1.1 V, respectively. After each potential step, the applied potential was returned to 0.0 V and it was confirmed that n...

The determination of the electronic states of single-walled carbon nanotubes (SWNTs) with a specific chirality has been a central issue in the science of SWNTs. Here we present the empirical equations with fitting parameters for the determination of the reduction and oxidation potentials of SWNTs for a wide range of diameters and chiral angles. In these equations, a distinct chirality family dependence of the reduction potentials is observed, while the oxidation potentials show a simple diameter dependence nearly proportional to the inversed nanotube diameter. Based on observations of the asymmetric chirality dependence between the reduction and oxidation potentials, the Fermi levels of the SWNTs were revealed to have a definite chirality family dependence, which indicates that the work functions of the SWNTs with small diameters deviate from the values for the large diameter SWNTs and graphene. We also performed quantum chemical calculations to compare the experiment to the calculations.

Understanding the doping mechanism that involves substantial charge transfer between carbon nanotubes and chemical adsorbent is of critical importance for both basic scientific knowledge and nanodevice applications. Nevertheless, it is difficult to estimate the modification of electronic structures of the doped carbon nanotubes. Here we report measurements of electrochemical potentials of n-doped single-walled carbon nanotubes (SWCNTs) by using photoluminescence (PL) measurement. The change of the measured PL intensity before and after n-type doping was used to extract the electrochemical potential using the Nernst equation. The measured electrochemical potentials of SWCNTs approached the theoretical reduction potential of SWCNTs as the mole concentration of the dopant increased. The doping effect was also confirmed by the change of absorption spectroscopy. The quenching of the PL and absorption intensity was strongly correlated to the standard reduction potential of the dopant and its concentration. This investigation could be a cornerstone for SWCNTs-based electronic device applications such as solar cells, light-emitting diodes, and nanogenerators.

The determination of electronic states of single-walled carbon nanotubes (SWNTs) has been a central issue in science and nanotechnology of carbon nanotubes. Previously, we reported the electronic states of (n,m)SWNTs that were embedded in an anionic polymer, carboxymethylcellulose sodium salt (CMC). It is important to reveal how the electronic properties of individual (n,m)SWNTs are affected by the surrounding microenvironment. In this study, we focused on the effect of charge of the SWNT solubilizers. We used a cationic polymer, hydroxyethylcellulose ethoxylate (quaternized) (HEQ) as the SWNT solubilizer in place of CMC, and the isolated (n,m)SWNTs were embedded in a film of HEQ (matrix polymer) on an electrode. We found that the charge of HEQ virtually does not affect the electronic parameters, i.e., oxidation/reduction potentials, Fermi levels, and band gaps of the (n,m)SWNTs, indicating that the presented electronic parameters are the parameters of the intrinsic (n,m)SWNTs.Single-walled carbon nanotubes (SWNTs) are a group of nanomaterials that have a cylindrical shape, but different chiralities. The structures of the SWNTs are identified by a "chiral index" denoted (n,m) that specifies the diameter and chiral angle. The chiral index (n,m) is a dominant factor in determining the electronic properties of the SWNTs (i.e., electronic structure, Fermi levels, band gaps, and redox potentials). 810 Particularly, in situ Raman spectroelectrochemistry is a well-established method. Doping of SWNTs can be controlled precisely and the doping effect to Raman spectra has been discussed intensively.11,12 However, the achieved success in the determination of the redox properties as already reported has been low. It is not easy to determine the redox potentials of isolated (n,m)SWNTs using these methods since SWNTs with several different chiral indices have band gaps in the near-IR region that overlap one another.Photoluminescence (PL) spectroscopy is one of the most effective methods to investigate the optical properties of semiconducting SWNTs. 13 Chiralities of semiconducting SWNTs in a sample and their electronic interband transition energy can be identified by this method. SWNTs are synthesized as bundles containing many different chiralities of semiconducting and metallic SWNTs. Bundles of the SWNTs do not exhibit PL due to the presence of metallic SWNTs that quench the PL of the semiconducting SWNTs. Therefore, SWNTs should be solubilized in individually isolated states by the aid of dispersants 14 in order to detect their PL spectra.We have previously reported a PL spectroelectrochemical method that determines the redox potentials of the individual (n,m) SWNTs,15 in which the SWNTs were individually solubilized in a cast film of carboxymethylcellulose sodium salt (CMC, Figure 1a), an anionic cellulose polymer, 16 on an ITO electrode. Based on the redox potentials of SWNTs obtained by this method, chirality selective reactions of SWNTs 17 can be described quantitatively. During the redox reactions, electrons are wit...