Sp2 Carbon Network Research Articles

Vibrationally resolved deep–red circularly polarised luminescence spectra of C70 derivative through Gaussian curvature analysis of ground and excited states

Over the last years, the interaction of fullerene with circularly polarized light has attracted growing attention for potential electronic and optical applications. However, in literature there is only one example of fullerene derivative capable of emitting circularly polarized light, showing an active circularly polarized luminescence (CPL) signal in the deep-red visible region. This unique luminophore offered us the possibility to study the connection between the topological features of C70 spheroid and its chiral emission properties. In light of these considerations, we proposed a theoretical protocol that combines three different step: (1) The Ball Pivoting Algorithm for C70 surface reconstruction. (2) The discrete gaussian curvature analysis in the ground (S0) and excited states (S1). (3) The computation of the vibrationally-resolved CPL spectrum. The first step allowed us to extract useful information that linked the topological shape of C70 to the sp2 carbon network chemistry. The DFT benchmark in the second step guided us in grasping the best functional for the C70 curvature simulation in the ground state, spotlighting how B97D3 excellently succeed for this task. The curvature investigation in the first excited state showed that (for all the twenty exchange–correlation functional tested) the C70 fragment is more curved in S1 than in S0. The final step collected the topological information from the previous sections to provide a detailed overview of the theoretical factors (such as the quantum formalism, the potential energy surface description and the transition dipole moment approximation) impacting on the C70 vibrationally resolved CPL spectrum. We found that the adiabatic hessian model coupled with the Franck-Condon Herzberg-Teller approximation computed at PW6B95D3/6-311G(d,p) level provides excellent results in emulating the band-shape and position of the experimental CPL spectrum.

Nitrogen-Doped Single-Walled Carbon Nanotubes by Floating-Catalyst CVD Process

Due to the properties of single-walled carbon nanotube (SWCNT), thin film SWCNTs have been used for many versatile applications. Direct synthesis of the nanotube films with desired electronic structures without prerequisite of post treatment process then becomes one important step. Here, we present the synthesis of nitrogen-doped SWCNTs by floating-catalyst chemical vapor deposition process. With low nitrogen level incorporated into the sp2 carbon network, substitutional and pyridinic nitrogens become predominance. The electronic structure of N-doped SWCNT film could be changed into n-type doping. The localized structures of carbon and nitrogen bonding environments were also revealed by x-ray absorption spectroscopy. The formation of p-n junction was also obtained from the I-V characteristic of N-doped SWCNT heterojunction diode revealing n-type behavior of the sample.

(Invited) Microenvironment Responsiveness of Defect Photoluminescence of Locally Functionalized Single-Walled Carbon Nanotubes and Its Sensing Applications

Photoluminescence (PL) of single-walled carbon nanotubes (SWCNTs) in the near infrared (NIR) region is applicable to advanced optical applications such as bio-imaging and sensing. Local chemical functionalization (slight amount of chemical modification) of SWCNTs has been developed to introduce sp3 carbon defects in the sp2 carbon network of the tube walls for the luminescent defect formation.[1-3] The resultant locally functionalized SWCNTs (lf-SWCNTs) show defect PL (E 11* PL) with red-shifted wavelengths and increased quantum yields compared to original E 11 PL of pristine SWCNTs. For lf-SWCNTs, molecularly designed modifier molecules have enabled the defect PL wavelength modulation[4] and the sensing function creation.[5,6]Recently, we have reported the unique microenvironment responsiveness of defect PL of lf-SWCNTs; namely, the greater wavelength shifts of E 11* PL than E 11 PL by dielectric effects[7] and the PL shifting behavior modulation based on the chemical structure difference of the functionalized sites and the exciton localization effects[8] were observed. The microenvironment responsiveness of the defect PL was applied to the biological sensing application development.[9] To investigate protein detection/recognition functions of lf-SWCNTs, we introduced an avidin-biotin interaction with a selective and strong binding fashion at the functionalized sites of lf-SWCNTs. The lf-SWCNTs tethering biotin groups (lf-SWCNTs-b) were synthesized through diazonium chemistry, followed by its subsequent-modification. When neutravidin was mixed with a lf-SWCNTs-b solution, E 11* PL peak was red-shifted, indicating the higher polarity environment formation by the neutravidin adsorption on lf-SWCNTs-b. When avidin or streptavidin was used, wavelength shifting behaviors of E 11* PL of lf-SWCNTs-b were clearly changed depending on the used avidin derivatives. The results indicate the different polarity environment formation deriving from structural differences of each avidin derivative. Moreover, the detection signal enhancement was observed in a film device using lf-SWCNTs-b. Therefore, lf-SWCNTs have a high potential for development of advanced protein detection/recognition systems using NIR PL.[1] T. Shiraki et al. Acc. Chem. Res., 53, 1846 (2020). [2] S. Tretiak et al., Acc. Chem. Res., 53, 1791(2020) [3] Y. Wang et al. Nat. Rev. Chem., 3, 375 (2019). [4] T. Shiraki et al. ACS Nano, DOI: 10.1021/acsnano.2c09897 (2022). [5] T. Shiraki et al. Chem. Commun., 52, 12972 (2016). [6] S. Kruss et al, Angew. Chem. Int. Ed., 59, 17732 (2020). [7] T. Shiraki et al. Chem. Commun., 55, 3662 (2019). [8] T. Shiraki et al. J. Phys. Chem. C, 125, 12758 (2021). [9] T. Shiraki et al. Nanoscale, 14, 13090 (2022). Figure 1

The photophysics of distorted nanographenes: Ultra-slow relaxation dynamics, memory effects, and delayed fluorescence

The controlled deformation and engineering of the sp2 carbon network in atomically-precise nanographenes, and their substantially larger size as compared to typical optical dyes, opens new opportunities for the modulation of optical and electronic properties, but the peculiar photophysics of these systems is still poorly understood. Here, through a detailed comparative study of two well-defined distorted nanographenes, we show that they can exhibit interesting photophysical features, such as triplet-triplet annihilation delayed fluorescence, ultra-slow excited state dynamics, and excitation-wavelength memory effects on the nanosecond and sub-nanosecond relaxation cascades. Some of these behaviours are highly unexpected and strongly deviate from the archetypal behaviour of typical optical dyes. The distortion of the sp2 network was obtained by means of a non-hexagonal ring and a helicene unit, introduced by taking advantage of the high control provided by specific bottom-up organic synthesis. We believe the rich conformational landscape provided by the combination of the saddle-shaped curvature due to the heptagon ring and the helicene edge is at the heart of the uncommon photophysics.

Chemistry of zipping reactions in mesoporous carbon consisting of minimally stacked graphene layers.

The structural evolution of highly mesoporous templated carbons is examined from temperatures of 1173 to 2873 K to elucidate the optimal conditions for facilitating graphene-zipping reactions whilst minimizing graphene stacking processes. Mesoporous carbons comprising a few-layer graphene wall display excellent thermal stability up to 2073 K coupled with a nanoporous structure and three-dimensional framework. Nevertheless, advanced temperature-programmed desorption (TPD), X-ray diffraction, and Raman spectroscopy show graphene-zipping reactions occur at temperatures between 1173 and 1873 K. TPD analysis estimates zipping reactions lead to a 1100 fold increase in the average graphene-domain, affording the structure a superior chemical stability, electrochemical stability, and electrical conductivity, while increasing the bulk modulus of the framework. At above 2073 K, the carbon framework shows a loss of porosity due to the development of graphene-stacking structures. Thus, a temperature range between 1873 and 2073 K is preferable to balance the developed graphene domain size and high porosity. Utilizing a neutron pair distribution function and soft X-ray emission spectra, we prove that these highly mesoporous carbons already consist of a well-developed sp2-carbon network, and the property evolution is governed by the changes in the edge sites and stacked structures.

(Digital Presentation) Excitonic Photoluminescence Properties of Locally Functionalized Single-Walled Carbon Nanotubes Using Molecular Modifiers

Excitons in single-walled carbon nanotubes (SWCNTs) show unique properties due to strong quantum confinement and weak dielectric screening effects which give rise to high binding energies based on strong Coulombic interactions. By this feature, stable and mobile excitons are generated in SWCNTs and its radiative recombination produces photoluminescence (PL) in the near infrared (NIR) region. Recently, local chemical functionalization of SWCNTs has attracted great attention because of enhancement of their NIR PL properties.[1-5] This functionalization dopes local defects such as sp3 carbon to the semiconducting sp2 carbon networks of SWCNTs based on the covalent bond formation between the tube walls and modifier molecules. As a result, emissive doped sites that have narrower band gaps and exciton trapping features are created in the locally functionalized SWCNTs (lf-SWCNTs). For lf-SWCNTs, E 11* PL newly appears with red-shifted wavelengths and increased PL quantum yields compared with original E 11 PL of pristine SWCNTs. Currently, chemical functionalization methods and E 11* PL wavelength modulation techniques are being developed for further functionalization of lf-SWCNTs. [1-5] In this presentation, E 11* PL properties of lf-SWCNTs synthesized using newly designed chemical modifiers are discussed. For example, an azide compound is found to produce the emissive doped sites in lf-SWCNTs via a [2+1] cycloaddition reaction. The E 11* PL peak was observed at 1118 nm and N1s peak in X-ray photoelectron spectroscopy was detected around 400 eV regions based on the chemical bond formation. Moreover, solvatochromic PL energy shifts of the E 11* PL showed a different trend from those observed for typical lf-SWCNTs synthesized using diazonium chemistry. This result indicates that the chemical structures of the doped sites could be a key factor to modulate excitonic properties of localized excitons in lf-SWCNTs. Therefore, the molecular chemistry approach would provide unique exciton engineering tools for lf-SWCNTs and develop advanced excitonic NIR materials applicable to quantum cryptography technologies and high-performance bio/medical imaging and sensing.[1] T. Shiraki, Chem. Lett., 50, 397 (2021); [2] T. Shiraki et al., Acc. Chem. Res., 53, 1846 (2020); [3] S. Tretiak et al., Acc. Chem. Res., 53, 1791 (2020); [4] Y. Wang et al., Nat. Rev. Chem., 3, 375 (2019); [5] J. Zaumseil, Adv. Optical Mater. 2101576 (2021).

(Invited, Digital Presentation) Ortho-Substituent Structure Design in Aryldiazonium Salts for Defect Photoluminescence Modulation of Locally Functionalized Single-Walled Carbon Nanotubes

Photoluminescence (PL) of single-walled carbon nanotubes (SWCNTs) appears in the near infrared (NIR) region, which is applicable to advanced optical applications such as bioimaging and telecommunication devices. Local chemical functionalization of SWCNTs has been gathering great attention because of the enhancement of their NIR PL properties. Therein, defects such as sp3 carbon are locally doped to the crystalline sp2 carbon network of the tube walls by the chemical functionalization process.[1-4] As a result, the locally functionalized SWCNTs (lf-SWCNTs) emit new PL with red-shifted wavelengths and increased quantum yields from the doped sites (E 11* PL) compared to original E 11 PL of pristine SWCNTs. It is due to the doping effects to change electronic structures for narrower bandgap formation, by which mobile excitons in the tubes are trapped at the doped sites to be localized states for efficient PL conversion.The chemical functionalization approach allows us to use various chemical reactants for the doped site formation in lf-SWCNTs. The molecular effects including structural differences and molecular binding functions have resulted in versatile NIR PL wavelength modulation of lf-SWCNTs.[1-4] We have reported that E 11* PL generation phenomena were significantly varied depending on isomeric structures of substituted aryldiazonium salts (AD) used for lf-SWCNT synthesis.[5] Especially, ortho-substituted ADs (oADs) produced two PL around 1100 and 1250 nm-regions, respectively for the resulting lf-SWCNTs with (6,5) chirality. Here, we apply various substituent design for oADs and examine the substituent structure effects in terms of modulation of the PL emission properties of lf-SWCNTs. For example, oAD having a phenyl substituent resulted in enhancement of the ~1250 nm PL contribution. Other substituent effects are observed depending on substituent structures of oADs, from which interactions between the substituents and the tubes are considered to induce the observed PL spectral changes. The result indicates that local chemical functionalization using oAD has a high potential to largely modulate NIR PL wavelengths of lf-SWCNTs beyond 1000 nm regions.[1] T. Shiraki et al. Acc. Chem. Res., 53, 1846 (2020). [2] S. Tretiak et al., Acc. Chem. Res., 53, 1791(2020) [3] Y. Wang et al. Nat. Rev. Chem., 3, 375 (2019). [4] T. Shiraki, Chem. Lett., 50, 397 (2021). [5] T. Shiraki et al. Chem. Commun., 53, 12544 (2017).

Van der Waals Epitaxy of Organic Semiconductor Thin Films on Atomically Thin Graphene Templates for Optoelectronic Applications.

ConspectusOrganic semiconductors (OSCs) offer unique advantages with respect to mechanical flexibility, low-cost processing, and tunable properties. The optical and electrical properties of devices based on OSCs can be greatly improved when an OSC is coupled with graphene in a certain manner. Our research group has focused on using graphene as a growth template for OSCs and incorporating such high-quality heterostructures into optoelectronic devices. The idea is that graphene's atomically flat surface with a uniform sp2 carbon network can serve as a perfect quasi-epitaxial template for the growth of OSCs. In addition, OSC-graphene heterostructures benefit from graphene's unique characteristics, such as its high charge-carrier mobility, excellent optical transparency, and fascinating mechanical durability and flexibility.However, we have often found that OSC molecules assemble on graphene in unpredictable manners that vary from batch to batch. From observations of numerous research systems, we elucidated the mechanism underlying such poor repeatability and set out a framework to actually control the template effect of graphene on OSCs. In this Account, we not only present our scientific findings in this spectrum of areas but also convey our research scheme to the readers so that similar heterostructure complexes can be systematically studied.We began with experiments showing that the growth of OSCs on a graphene surface was driven by van der Waals interactions and is therefore sensitive to the cleanliness of the graphene surface. Nonetheless, we noted that, even on similarly clean graphene surfaces, the OSC thin film still varied with the underlying substrate. Thanks to the graphene-transfer method and in situ gating methods that we developed, we discovered that the decisive parameter for molecule-graphene interaction (and, hence, for the growth of OSCs on graphene) is the charge density in the graphene. Thus, to prepare a graphene template for high-quality graphene-OSC heterostructures, we controlled the charge density in the graphene to minimize the molecule-graphene interaction. Moreover, the possible charge transfer between OSC molecules and graphene, which induces additional molecule-graphene interactions, should also be taken into account. Eventually, we demonstrated a wide range of optoelectronic applications that benefitted from high-quality OSC-graphene heterostructures fabricated using our proof-of-concept systems.

Achieving superlubricity using selected tribo-pairs lubricated by castor oil and unsaturated fatty acids

Systematic friction tests have been performed to unveil the key factors for reaching superlubricity (CoF < 0.01) in the presence of unsaturated fatty acid-based lubricants under boundary lubrication regime. The impact of different tribo-pairs and lubricants has been investigated. When the counterpart is steel, results show that a hydrogen-free DLC coating is indispensable to achieve superlubricity in castor oil. Among pure unsaturated fatty acids as lubricants, oleic and ricinoleic acid gave superlow friction but linoleic acid is not recommended to lubricate steel/a-C contact due to the occurrence of high friction and wear. X-ray photoelectron spectroscopy (XPS) and X-Ray-Excited Auger Electron Spectroscopy (XAES) analyses reveal that hydrogen-free carbon can activate two pathways to passivate surface and to achieve superlubricity with fatty acid-based lubricants (i) carbon re-hybridization by forming a high-density sp2 carbon network and (ii) –(CH2-CH2)n– oligomers formation on top surface. At the opposite, linoleic acid hinders the formation of –(CH2-CH2)n– oligomers and oxidizes carbon surfaces.

Successive Free-Radical C(sp 2 )–C(sp 2 ) Coupling Reactions to Form Graphene

Successive Free-Radical C(sp ² )–C(sp ² ) Coupling Reactions to Form Graphene

Novel Graphene Wool Gas Adsorbent for Volatile and Semivolatile Organic Compounds.

Volatile and semivolatile organic compounds in ambient air and occupational settings are of great concern due to their associated adverse human health and environmental impacts. Novel graphene wool samplers have been developed and tested to overcome limitations of commercially available sorbents that can only be used once and typically require solvent extraction. Graphene wool (GW) was synthesized by non-catalytic chemical vapor deposition with optimized conditions, resulting in a novel fibrous graphene wool that is very easy to manage and less rigid than other forms of graphene, lending itself to a wide range of potential applications. Here, the air pollutant sampling capabilities of the GW were of interest. The optimal packing weight of GW inside a glass tube (length 178 mm, i.d. 4 mm, o.d. 6 mm) was investigated by the adsorption of vaporized alkane standards on the GW, using a condensation aerosol generator in a temperature-controlled chamber and subsequent detection using a flame ionization detector. The optimized GW packing density was found to be 0.19 mg mm–3 at a flow rate of 500 mL min–1, which provided a gas collection efficiency of >90% for octane, decane, and hexadecane. The humidity uptake of the sampler is less than 1% (m/m) for ambient humidities <70%. Breakthrough studies showed the favorable adsorption of polar molecules, which is attributed to the defective nature of the graphene and the inhomogeneous coating of the graphene layers on the quartz wool, suggesting that the polar versus non-polar uptake potential of the GW can be tuned by varying the graphene layering on the quartz wool substrate during synthesis. Oxidized domains at the irregular edges of the graphene layers, due to a broken, non-pristine sp2 carbon network, allow for adsorption of polar molecules. The GW was applied and used in a combustion sampling campaign where the samplers proved to be comparable to frequently used polydimethylsiloxane sorbents in terms of sampling and thermal desorption of non-polar semivolatile organic compounds. The total alkane concentrations detected after thermal desorption of GW and PDMS samplers were found to be 17.96 ± 13.27 and 18.30 ± 16.42 μg m–3, respectively; thus, the difference in the alkane sampling concentration between the two sorbent systems was negligible. GW provides a new, exciting possibility for the monitoring of organic air pollutants with numerous advantages, including high sampling efficiencies, simple and cost-effective synthesis of the thermally stable GW, solvent-free and environmentally friendly analysis, and, importantly, the reusability of samplers.

A hybrid molecular peapod of sp2- and sp3-nanocarbons enabling ultrafast terahertz rotations

The internal hollow space of carbon nanotubes provides a unique nanometre-sized space to capture various molecular entities. The inner space circumfused by sp2-carbon networks can also encapsulate diamondoid molecules to afford sp2/sp3-hybrid nanocarbon peapods that have recently emerged as unique nanostructures. In this study, the sp2/sp3-hybrid peapods have been mimicked by adopting a cylindrical molecule and the smallest diamondoid, i.e., adamantane, to demonstrate the existence of ultrafast rotational motion. The solid-state rotational frequency is measured by NMR spectroscopy to record 1.06 THz that is, to the best of our knowledge, the largest value recorded for solid-state rotations of molecules. Theoretical calculations reveal that multivalent CH-π hydrogen bonds anchored the diamondoid guest on the π-wall of the cylindrical host. The weak hydrogen bonds are prone not only to cleave but also to regenerate at the interfaces, which give freedom to the guest for ultrafast isotropic rotations in the inertial regime.

(Invited) Molecular Structure-Based Photoluminescence Modulation of Locally Functionalized Single-Walled Carbon Nanotubes Using Bis-Aryl Functionalization

Single-walled carbon nanotubes (SWCNTs) show photoluminescence (PL) in the near infrared (NIR) region, which is applicable to bioimaging and telecommunication devices. Recently, local chemical functionalization of SWCNTs has been developed to enhance their NIR PL properties, in which defects such as sp3 carbon are locally doped to the crystalline sp2 carbon network of the tube walls by the functionalization.[1-3] Actually, E 11* PL of the locally functionalized SWCNTs (lf-SWCNTs) is observed with red-shifted wavelengths and increased quantum yields compared to original E 11 PL of pristine SWCNTs. It is due to formation of new emissive sites with narrower band gaps and exciton trapping features in the tube structures.In the local chemical functionalization, doped site structures of the lf-SWCNTs can be changed depending on modifier molecules, which results in effective modulation of the NIR PL wavelengths of the lf-SWCNTs beyond 1000 nm-region. Previously, we have developed bis-aryldiazonium salts (bAs) that have two reactive aryldiazonium groups connected with a methylene linker and observed E 11 2* PL over 1200 nm regions from the lf-SWCNTs with (6,5) chirality based on its proximal aryl functionalization.[4]Here, we synthesize new modifier molecules with the bis-aryldiazonium motif and modify the geometry of the proximal aryl-functionalized sites of the lf-SWCNTs. As a result, for example, methylene linker positions on the aryldiazonium groups of bAs clearly changed the trend of methylene length-dependent wavelength shifts of E 11 2* PL. [5] Moreover, bAs having rigid linker structures changed peak positions of E 11 2* PL, indicating that the control of the proximal defect configuration would be an effective way for the PL property modulation of lf-SWCNTs. As another aspect of the proximal aryl functionalization, we found that E 11 2* PL showed unique wavelength shift behaviors by microenvironment changes using various organic solvents. The observed trend was different from those of E 11 PL and E 11* PL[6], in which proximal defect distances could be an important factor for their microenvironment responsiveness.Therefore, molecularly designed bis-aryldiazonium modifiers become promising tools to create structurally controlled bis-aryl functionalized sites of lf-SWCNTs and precisely modulate their NIR PL wavelengths (> 1000 nm).[1] T. Shiraki et al. Acc. Chem. Res., 53, 1846 (2020). [2] S. Tretiak et al., Acc. Chem. Res., 53, 1791(2020) [3] Y. Wang et al. Nat. Rev. Chem., 3, 375 (2019). [4] T. Shiraki et al. Sci. Rep., 6, 28393 (2016). [5] T. Shiraki et al. Chem. Lett., 48, 791 (2019). [6] T. Shiraki et al. Chem. Commun., 55, 3662 (2019). Figure 1

Biopolymer Derived Thin Carbon Film As a Novel Sensing Material for Low-Cost Resistive and Fast-Response Humidity Sensors

Introduction Recently, fast response humidity sensors are an active area of research for applications such as industrial, agricultural and point of care devices. Among various types of humidity sensor materials, thin film based resistive humidity sensors have been actively studied because those exhibit high surface area and the sensor configuration is simple. However, most of these sensors are relatively slow with long response time (over 60 seconds) and narrow detection limits (30-50 RH%), making them difficult to use in many applications [1-2]. Besides, the need of an external heater for fast response increases power consumption and complicates the manufacturing process of the sensor. Functionalized graphene, the most popular humidity sensor material, offers significant advantages due to its unique 2D structure and oxygen-containing functional groups, providing a large surface reaction site. However, it also has limitations such as poor stability in a moist environment due to its hydrophilic nature and weak adhesion with the substrate, complex synthesis procedure, makes it difficult to develop practical sensing devices.Here, we developed the low-cost and fast-response humidity sensors by integration of thermally decomposed carbon (TDC) thin film and carbon nano-sized interdigitated electrodes (IDEs). Carbon IDEs were used as a sensor platform due to its excellent thermal compatibility with TDC films and it provides low-cost wafer-level fabrication of three-dimensional nanoelectrodes [3], resulting in the miniaturized sensor configuration at a wafer level. Shellac, a low-cost biopolymer, was used as a precursor for synthesizing TDC films via single-step pyrolysis. The obtained film showed conformal coating with no grain boundaries or defects and formed high sp2 hybridized carbon network on the carbon nano-sized IDEs, thus providing excellent stability, rapid response/recovery and low power consumption as a room temperature humidity sensor. Our results demonstrate the potential application of TDC film as an alternative sensing material for environmental humidity, instant calibration for gas sensing measurements and human respiration in real time. Methods We integrated a nanometer-thick TDC film onto the carbon nano-IDEs, using two-step process, to facilitate a simple and cost-effective humidity sensor. Firstly, microscale interdigitated polymer patterns were fabricated using photolithography and then pyrolyzed into nanoscale carbon IDEs due to volume reduction in pyrolysis. The interdigitated carbon nanoelectrodes were annealed at 1000 °C using a rapid thermal annealing process to enhance the electrical conductivity. The next step is the integration of a TDC film on the carbon IDEs. For that, shellac solution (4 wt.%) was uniformly spray-coated on the carbon IDEs and air-dried (1 hour). This shellac film was pyrolyzed at 600 °C to obtain a uniform TDC thin film. Results and Conclusions Figure a shows a scanning electron microscopy (SEM) image of the TDC coated nano-sized carbon IDEs (width = 800 nm, height = 300 nm, gap = 2.5 μm). The film displays a conformal coating with no signature of defects or grain boundaries. The electrical properties of TDC film were evaluated using a two-probe I-V technique (Figure b), which indicated the excellent ohmic contact with carbon IDEs. Raman spectra of the TDC film (Figure c) indicated the presence of local intrinsic defects and disorder (intense D band) due to the presence of oxygen functional groups, especially at the edges and basal plane of the TDC film. X-ray photoelectron spectroscopy (XPS) for carbon (Figure d) also confirmed the presence of oxygen-containing functional groups (C-OH and C=O) and a high sp2 hybridized carbon network. Higher dynamic response (40 %) is attributed to the presence of oxygen functional groups (Figure e), whereas sp2 carbon network induce hydrophobicity, which lowers the condensation of water molecules without using any external heating source, resulted in fast response (37s) and recovery time (8s) (Figure f), compared to previously reported rGO-based sensors [4]. The obtained thin film humidity sensor also displayed the linear response over the wide humidity range (10-90 RH%), with high sensitivity > 0.7/RH%. The dynamic response of the sensor revealed that the protonic conduction mechanism is dominant in TDC film.

Protonic acid catalysis to generate fast electronic transport channels in O-functionalized carbon textile with enhanced energy storage capability

Oxygen (O) functionalized carbon materials can provide high charge storage because of their enrichment in redox-active sites, but they do not display fast charge transfer kinetics, which is caused by the loss of electrical conductivity from the disruption of sp2 carbon networks. To address this challenge, we develop a novel two-step protonic acid catalysis method that partially re-establishes a π-π conjugated system for engineering fast electronic transport channels in an O-functionalized carbon textile. This method largely maintains the sp2 carbon network integrity with abundant active O-functional groups embedded into a graphitic carbon host. The resultant functionalized carbon textile features both high O-content and high electrical conductivity. When incorporated in flexible electrodes for supercapacitors, the material exhibits ultrahigh areal capacitance of 2580 mF cm−2 and excellent rate performance, outperforming other reported carbon-based flexible electrodes. The constructed flexible supercapacitor also delivers excellent electrochemical performance and mechanical stability under flexible deformations. Such a system might shed light on the design of O-functionalized carbon materials with both high O-content and high electrical conductivity for energy storage/conversion.

Carbon Nanotube Photoluminescence Modulation by Local Chemical and Supramolecular Chemical Functionalization.

ConspectusCarbon nanotubes (CNTs) have been central materials in nanoscience and nanotechnologies. Single-walled CNTs (SWCNTs) consisting of a cylindrical graphene show a metallic (met) or semiconducting (sc) property depending on their rolling up manner (chirality). The sc-SWCNTs show characteristic chirality-dependent optical properties of their absorption and photoluminescence (PL) in the near-infrared (NIR) region. These are derived from their highly π-conjugated structures having semiconducting crystalline sp2 carbon networks with defined nanoarchitectures that afford a strong quantum confinement and weak dielectric screening. Consequently, photoirradiation of the SWCNTs produces a stable and mobile exciton (excited electron-hole pair) even at room temperature, and the exciton properties dominate such optical phenomena in the SWCNTs. However, the mobile excitons decrease the PL efficiency due to nonradiative relaxation including collision with tube edges and relaxation to lower-lying dark states. A breakthrough regarding the efficient use of the mobile exciton for PL has recently been achieved by local chemical functionalization of the SWCNTs, in which the chemical reactions introduce local defects of oxygen and sp3 carbon atoms in the tube structures. The defect doping creates new emissive doped sites that have narrower band gaps and trap the mobile excitons, which provides locally functionalized SWCNTs (lf-SWCNTs). As a result, the localized exciton produces E11* PL with red-shifted wavelengths and enhanced PL quantum yields compared to the original E11 PL of the nonmodified SWCNTs.In this Account, we describe recently revealed fundamental properties of the lf-SWCNTs based on the analyses by photophysics, theoretical calculations, and electrochemistry combined with in situ PL spectroscopy. The new insight allows us to expand the wavelength regions of the NIR E11* PL derived from the localized exciton, in which upconversion generates a higher energy PL through thermal activation and proximal doped site formation using bis-aryldiazonium modifiers provides a much lower energy PL than typical E11* PL. Moreover, owing to the chemical reaction-dominant doping process, the molecular structure design of modifiers succeeds in producing functionalized lf-SWCNTs; namely, molecular functions are incorporated into the doped sites for their PL modulation. The wavelength changes/switching in the E11* PL selectively occurs by a supramolecular approach using molecular recognition and imine chemistry. Therefore, the local chemical functionalization of the SWCNTs is a key to designing the properties and creating their new functions of the lf-SWCNTs. Fundamental understanding of the doped site properties of the lf-SWCNTs and molecularly driven approaches for exciton and defect engineering would unveil the intrinsic natures of these materials, which is crucial for elevating the SWCNT-based nanotechnologies to the next stage. The resulting materials are of interest in the fields of high performance NIR-II imaging and sensing for bio/medical analyses and single-photon emitters in quantum information technology.

Multistage Self-Assembly Strategy: Designed Synthesis of N-doped Mesoporous Carbon with High and Controllable Pyridine N Content for Ultrahigh Surface-Area-Normalized Capacitance

Nitrogen doping could improve the performance of carbon materials in electrocatalysis, CO2 adsorption, and energy storage. [1]However, the control of the doping type and the amount of nitrogen (N)-...

Temperature and environment effects on the graphene oxide reduction via electrical conductivity studies

In this article, we report a study carried out to understand how changes in environment and temperature, in which the graphene oxide (GO) film reduction occurs, alter the electrical properties of the resulting films. In fact, it is possible to improve the GO reduction efficiency by choosing suitable environment and temperature. To this purpose, three different environments (high vacuum, air and nitrogen) and three dissimilar temperatures (177 °C, 300 °C and 600 °C) have been chosen, as suggested by differential scanning calorimetry (DSC) measurements. Among the investigated thermally reduced graphene oxide films, the ones treated at 600 °C in nitrogen have shown to possess higher electrical conductivity. Such an enhanced electrical conductivity can be attributed to reduction of oxygen functional groups and restoration of sp2 carbon network, as confirmed by Raman spectra.

(Invited) Photoinduced Donor-Acceptor Interaction in Nanocarbon-Based Systems

Nanographenes, characterized by well-defined planar structures of sp2 carbon network with sizes over 1 nm, have attracted tremendous attention, as their extended π-conjugation offers intriguing characteristics in optical and electronic properties, such as large extinction coefficients, high photoluminescence quantum yields, and excellent charge transport abilities. These properties suggest their potential utility as basic components in various electronic devices including light-emitting diodes, solar cells, and field-effect transistors. Along this line, nanographenes with different sizes and edge configurations have been prepared, demonstrating the possibility of fine-tuning their electronic and optoelectronic properties through the structural modulation. Among them, hexa-peri-hexabenzocoronenes (HBCs) consisting of 42 sp2 carbons in the π-conjugated core can be regarded as the minimum unit of nanographenes. In contrast with nanographene molecules, other two-dimensional (2D) nanocarbons such as graphenes, graphene oxides (GOs), chemically-converted graphenes (CCGs), and graphene quantum dots (GQDs) are structurally inhomogeneous at the molecular level, containing different π-conjugation sizes, edge structures, and defect sites. Nanographenes can be regarded as a part of the larger 2D nanocarbons, and therefore, π-extended HBC derivatives with well-defined structures are ideal model units to understand the intrinsic structure–property correlations of the 2D nanocarbons.Covalent linking of nanographenes and photoactive molecules is an effective strategy to endow them with new functions, as well as to examine their optical and photophysical properties, without changing the nanographene core structures. Various HBC linked systems with photoactive molecules including porphyrins, perylene diimides, and fullerenes were prepared and their basic optical properties such as steady-state absorption and fluorescence spectra were investigated. Nevertheless, so far such covalent functionalization of nanographenes has been limited to HBCs solely, and, to the best of our knowledge, covalently linked systems of photoactive molecule–nanographenes larger than HBC have never been reported. Therefore, the size and shape effects of nanographenes on the optical and photophysical properties of nanographene–photoactive molecule linked systems have yet to be studied systematically.To this end, we employed two nanographenes as the model: the symmetrical HBC and its π-extended rectangular strip-shaped nanographene consisting of 114 sp2 carbons, which is a short graphene nanoribbon (GNR). They were linked with two zincporphyrin (ZnP) units through a p-phenylene bridge at the periphery positions for the better understanding of their intrinsic properties. The short, rigid phenylene spacer ensures a well-defined geometry between the nanographene and the attached porphyrins. The HBC core was selected as a typical, basic example of nanographenes. Although various linked systems of HBC with photoactive molecules including porphyrins have already been reported, ZnP–HBC linked systems with the p-phenylene spacer have yet to be synthesized. Meanwhile the GNR core was chosen because of its closely related structure to HBC. GNR possesses the same size on the short axis, but the large size on the long axis compared to HBC. Furthermore, GNR and HBC have the same edge structures, which provides an opportunity to focus on the size effect of nanographenes.In this talk, I will give an overview of photoinduced donor-acceptor interaction in nanocarbon-based systems. For instance, photoexcitation of the porphyrin–HBC linked system led to exclusive energy transfer (EnT) from the first singlet excited state (S1) of the nanographene to the porphyrin, whereas opposite selective EnT occurred from the first and second singlet excited states (S1 and S2) of the porphyrin to the nanographene in the porphyrin–GNR linked system. In particular, ultrafast efficient EnTs from both the S2 and S1 states of the porphyrin to GNR mimic the corresponding ultrafast EnTs from the S2 and S1 states of carotenoids to chlorophylls in light-harvesting systems of natural photosynthesis. Such unique photophysical properties will be useful for the rational design of carbon-based photofunctional nanomaterials in optoelectronics and solar energy conversion devices.[1] X. Liu, M. Kozlowska,T. Okkali, D. Wagner,T. Higashino, G. Brenner-Weiß, S. Marschner, Z. Fu, Q. Zhang, H. Imahori, S. Bräse, W. Wenzel,C. Wöll, L. Heinke, Angew. Chem. Int. Ed., 58, 9590 (2019).[2] T. Umeyama, T. Hanaoka, H. Yamada, Y. Namura, S. Mizuno, T. Ohara, J. Baek, J. Park, Y. Takano, K. Stranius, N. V. Tkachenko, H. Imahori, Chem. Sci., 10, 6642 (2019).

Biopolymer Derived Thin Carbon Film As a Novel Sensing Material for Low-Cost Resistive and Fast-Response Humidity Sensors

Introduction Recently, fast response humidity sensors are an active area of research for applications such as industrial, agricultural and point of care devices. Among various types of humidity sensor materials, thin film based resistive humidity sensors have been actively studied because those exhibit high surface area and the sensor configuration is simple. However, most of these sensors are relatively slow with long response time (over 60 seconds) and narrow detection limits (30-50 RH%), making them difficult to use in many applications [1-2]. Besides, the need of an external heater for fast response increases power consumption and complicates the manufacturing process of the sensor. Functionalized graphene, the most popular humidity sensor material, offers significant advantages due to its unique 2D structure and oxygen-containing functional groups, providing a large surface reaction site. However, it also has limitations such as poor stability in a moist environment due to its hydrophilic nature and weak adhesion with the substrate, complex synthesis procedure, makes it difficult to develop practical sensing devices.Here, we developed the low-cost and fast-response humidity sensors by integration of thermally decomposed carbon (TDC) thin film and carbon nano-sized interdigitated electrodes (IDEs). Carbon IDEs were used as a sensor platform due to its excellent thermal compatibility with TDC films and it provides low-cost wafer-level fabrication of three-dimensional nanoelectrodes [3], resulting in the miniaturized sensor configuration at a wafer level. Shellac, a low-cost biopolymer, was used as a precursor for synthesizing TDC films via single-step pyrolysis. The obtained film showed conformal coating with no grain boundaries or defects and formed high sp2 hybridized carbon network on the carbon nano-sized IDEs, thus providing excellent stability, rapid response/recovery and low power consumption as a room temperature humidity sensor. Our results demonstrate the potential application of TDC film as an alternative sensing material for environmental humidity, instant calibration for gas sensing measurements and human respiration in real time. Methods We integrated a nanometer-thick TDC film onto the carbon nano-IDEs, using two-step process, to facilitate a simple and cost-effective humidity sensor. Firstly, microscale interdigitated polymer patterns were fabricated using photolithography and then pyrolyzed into nanoscale carbon IDEs due to volume reduction in pyrolysis. The interdigitated carbon nanoelectrodes were annealed at 1000 °C using a rapid thermal annealing process to enhance the electrical conductivity. The next step is the integration of a TDC film on the carbon IDEs. For that, shellac solution (4 wt.%) was uniformly spray-coated on the carbon IDEs and air-dried (1 hour). This shellac film was pyrolyzed at 600 °C to obtain a uniform TDC thin film. Results and Conclusions Figure a shows a scanning electron microscopy (SEM) image of the TDC coated nano-sized carbon IDEs (width = 800 nm, height = 300 nm, gap = 2.5 μm). The film displays a conformal coating with no signature of defects or grain boundaries. The electrical properties of TDC film were evaluated using a two-probe I-V technique (Figure b), which indicated the excellent ohmic contact with carbon IDEs. Raman spectra of the TDC film (Figure c) indicated the presence of local intrinsic defects and disorder (intense D band) due to the presence of oxygen functional groups, especially at the edges and basal plane of the TDC film. X-ray photoelectron spectroscopy (XPS) for carbon (Figure d) also confirmed the presence of oxygen-containing functional groups (C-OH and C=O) and a high sp2 hybridized carbon network. Higher dynamic response (40 %) is attributed to the presence of oxygen functional groups (Figure e), whereas sp2 carbon network induce hydrophobicity, which lowers the condensation of water molecules without using any external heating source, resulted in fast response (37s) and recovery time (8s) (Figure f), compared to previously reported rGO-based sensors [4]. The obtained thin film humidity sensor also displayed the linear response over the wide humidity range (10-90 RH%), with high sensitivity > 0.7/RH%. The dynamic response of the sensor revealed that the protonic conduction mechanism is dominant in TDC film.