Reconfiguring Organic Color Centers on the sp2 Carbon Lattice of Single-Walled Carbon Nanotubes

Correlation Measurements for Carbon Nanotubes with Quantum Defects

Single-photon sources are essential building blocks for the development of photonic quantum technology. Regarding potential practical application, an on-demand electrically driven quantum-light emitter on a chip is notably crucial for photonic integrated circuits. Here, we propose functionalized single-walled carbon nanotube field-effect transistors as a promising solid-state quantum-light source by demonstrating photon antibunching behavior via electrical excitation. The sp3 quantum defects were formed on the surface of (7, 5) carbon nanotubes by 3,5-dichlorophenyl functionalization, and individual carbon nanotubes were wired to graphene electrode pairs. Filtered electroluminescent defect-state emission at 77 K was coupled into a Hanbury Brown and Twiss experiment setup, and single-photon emission was observed by performing second-order correlation function measurements. We discuss the dependence of the intensity correlation measurement on electrical power and emission wavelength, highlighting the challenges of performing such measurements while simultaneously analyzing acquired data. Our results indicate a route toward room-temperature electrically triggered single-photon emission.

Solvent Isotope Effects on the Creation of Fluorescent Quantum Defects in Carbon Nanotubes by Aryl Diazonium Chemistry

The integration of aryl diazonium and carbon nanotube chemistries has offered rich and versatile tools for creating nanomaterials of unique optical and electronic properties in a controllable fashion. The diazonium reaction with single-wall carbon nanotubes (SWCNTs) is known to proceed through a radical or carbocation mechanism in aqueous solutions, with deuterated water (D2O) being the frequently used solvent. Here, we show strong water solvent isotope effects on the aryl diazonium reaction with SWCNTs for creating fluorescent quantum defects using water (H2O) and D2O. We found a deduced reaction constant of ∼18.2 times larger value in D2O than in H2O, potentially due to their different chemical properties. We also observed the generation of new defect photoluminescence over a broad concentration range of diazonium reactants in H2O, as opposed to a narrow window of reaction conditions in D2O under UV excitation. Without UV light, the physical adsorption of diazonium on the surface of SWCNTs led to the fluorescence quenching of nanotubes. These findings provide important insights into the aryl diazonium chemistry with carbon nanotubes for creating promising material platforms for optical sensing, imaging, and quantum communication technologies.

Control of functionalized single-walled carbon nanotube photoluminescence via competition between thermal rearrangement and elimination

We conducted the chiral separation of functionalized single-walled carbon nanotubes (SWNTs) with dibromopropane derivatives. Depending on their chirality and diameter, the thermal treatment of functionalized SWNTs leads to a shift in the emission radiation to longer wavelengths owing to rearrangement reaction in competition with elimination reaction.

Can armchair nanotubes host organic color centers?

We use time-dependent density functional theory to investigate the possibility of hosting organic color centers in (6, 6) armchair single-walled carbon nanotubes, which are known to be metallic. Our calculations show that in short segments of (6, 6) nanotubes∼5nm in length there is a dipole-allowed singlet transition related to the quantum confinement of charge carriers in the smaller segments. The introduction ofsp3defects to the surface of (6, 6) nanotubes results in new dipole-allowed excited states. Some of these states are redshifted from the native confinement state of the defect-free (6, 6) segments; this is similar behavior to what is observed withsp3defects to exciton transitions in semiconducting carbon nanotubes. This result suggests the possibility of electrically wiring organic color centers directly through armchair carbon nanotube hosts.

Electroluminescence from Single-Walled Carbon Nanotubes with Quantum Defects

Individual single-walled carbon nanotubes with covalent sidewall defects have emerged as a class of photon sources whose photoluminescence spectra can be tailored by the carbon nanotube chirality and the attached functional group/molecule. Here we present electroluminescence spectroscopy data from single-tube devices based on (7, 5) carbon nanotubes, functionalized with dichlorobenzene molecules, and wired to graphene electrodes. We observe electrically generated, defect-induced emissions that are controllable by electrostatic gating and strongly red-shifted compared to emissions from pristine nanotubes. The defect-induced emissions are assigned to excitonic and trionic recombination processes by correlating electroluminescence excitation maps with electrical transport and photoluminescence data. At cryogenic conditions, additional gate-dependent emission lines appear, which are assigned to phonon-assisted hot-exciton electroluminescence from quasi-levels. Similar results were obtained with functionalized (6, 5) nanotubes. We also compare functionalized (7, 5) electroluminescence data with photoluminescence of pristine and functionalized (7, 5) nanotubes redox-doped using gold(III) chloride solution. This work shows that electroluminescence excitation is selective toward neutral defect-state configurations with the lowest transition energy, which in combination with gate-control over neutral versus charged defect-state emission leads to high spectral purity.

Engineering defects with DNA

Single-walled carbon nanotubes are structurally modified by using a genetic sequence.

Quantum Defects: What Pairs with the Aryl Group When Bonding to the sp2 Carbon Lattice of Single-Wall Carbon Nanotubes?

Aryl diazonium reactions are widely used to covalently modify graphitic electrodes and low-dimensional carbon materials, including the recent creation of organic color centers (OCCs) on single-wall carbon nanotube semiconductors. However, due to the experimental difficulties in resolving small functional groups over extensive carbon lattices, a basic question until now remains unanswered: what group, if any, is pairing with the aryl sp³ defect when breaking a C═C bond on the sp² carbon lattice? Here, we show that water plays an unexpected role in completing the diazonium reaction with carbon nanotubes involving chlorosulfonic acid, acting as a nucleophilic agent that contributes -OH as the pairing group. By simply replacing water with other nucleophilic solvents, we find it is possible to create OCCs that feature an entirely new series of pairing groups, including -OCH₃, -OC₂H₅, -OC₃H₇, -i-OC₃H₇, and -NH₂, which allows us to systematically tailor the defect pairs and the optical properties of the resulting color centers. Enabled by these pairing groups, we further achieved the synthesis of OCCs with sterically bulky pairs that exhibit high purity defect photoluminescence effectively covering both the second near-infrared window and the telecom wavelengths. Our studies further suggest that these diazonium reactions proceed through the formation of carbocations in chlorosulfonic acid, rather than a radical mechanism that typically occurs in aqueous solutions. These findings uncover the unknown half of the sp³ defect pairs and provide a synthetic approach to control these defect color centers for quantum information, imaging, and sensing.

Polyoxometalate steric hindrance driven chirality-selective separation of subnanometer carbon nanotubes

Subnanometer single-chirality single-walled carbon nanotubes (SWCNTs) are of particular interest in multiple applications. Inspired by the interdisciplinary combination of redox active polyoxometalates and SWCNTs, here we report a cluster steric hindrance strategy by assembling polyoxometalates on the outer surface of subnanometer SWCNTs via electron transfer and demonstrate the selective separation of monochiral (6,5) SWCNTs with a diameter of 0.75 nm by a commercially available conjugated polymer. The combined use of DFT calculations, TEM, and XPS unveils the mechanism that selective separation is associated with tube diameter-dependent interactions between the tube and clusters. Sonication drives the preferential detachment of polyoxometalate clusters from small-diameter (6,5) SWCNTs, attributable to weak tube–cluster interactions, which enables the polymer wrapping and separation of the released SWCNTs, while strong binding clusters with large-diameter SWCNTs provide steric hindrance and block the polymer wrapping. The polyoxometalate-assisted modulation, which can be rationally customized, provides a universal and robust pathway for the separation of SWCNTs.

We develop a cluster steric hindrance strategy by assembling polyoxometalates on subnanometer single-walled carbon nanotubes (SWCNTs) and demonstrate the selective separation of single-chirality (6,5) SWCNTs via polymer extraction.