Solvatochromism of near infrared photoluminescence from doped sites of locally functionalized single-walled carbon nanotubes

Ratiometric fluorescent sensing of pyrophosphate with sp³-functionalized single-walled carbon nanotubes

Inorganic pyrophosphate is a key molecule in many biological processes from DNA synthesis to cell metabolism. Here we introduce sp3-functionalized (6,5) single-walled carbon nanotubes (SWNTs) with red-shifted defect emission as near-infrared luminescent probes for the optical detection and quantification of inorganic pyrophosphate. The sensing scheme is based on the immobilization of Cu2+ ions on the SWNT surface promoted by coordination to covalently attached aryl alkyne groups and a triazole complex. The presence of Cu2+ ions on the SWNT surface causes fluorescence quenching via photoinduced electron transfer, which is reversed by copper-complexing analytes such as pyrophosphate. The differences in the fluorescence response of sp3-defect to pristine nanotube emission enables reproducible ratiometric measurements in a wide concentration window. Biocompatible, phospholipid-polyethylene glycol-coated SWNTs with such sp3 defects are employed for the detection of pyrophosphate in cell lysate and for monitoring the progress of DNA synthesis in a polymerase chain reaction. This robust ratiometric and near-infrared luminescent probe for pyrophosphate may serve as a starting point for the rational design of nanotube-based biosensors.

Mixed-Solvent Engineering as a Way around the Trade-Off between Yield and Purity of (7,3) Single-Walled Carbon Nanotubes Obtained Using Conjugated Polymer Extraction

The inability to purify nanomaterials such as single-walled carbon nanotubes (SWCNTs) to the desired extent hampers the progress in nanoscience. Various SWCNT types can be purified by extraction, but it is challenging to establish conditions giving rise to the isolation of high-purity fractions. The problem stems from the fact that common organic solvents or water cannot provide an optimal environment for purification. Consequently, one must often decide between the separation yield and purity of the product. This article reports how through the self-synthesis of poly(9,9-dioctylfluorene-alt-benzothiadiazole) with tailored characteristics, in-depth elucidation of the extraction process, and mixed-solvent engineering, a high-yield isolation of monochiral (7,3) SWCNTs is developed. The combination of toluene and tetralin affords a separation medium of unique properties, wherein both high yield and exceptional purity can be attained simultaneously. The reported results pave the way for further research on this rare chirality, which, as illustrated herein, is much more reactive than any of the previously separated SWCNTs.

Functionalization of Carbon Nanotubes Surface by Aryl Groups: A Review

The review is devoted to the methods of introducing aryl functional groups to the CNT surface. Arylated nanotubes are characterized by extended solubility, and are widely used in photoelectronics, semiconductor technology, and bioelectrocatalysis. The main emphasis is on arylation methods according to the radical mechanism, such as the Gomberg-Bachmann and Billups reactions, and the decomposition of peroxides. At the same time, less common approaches are also considered. For each of the described reactions, a mechanism is presented in the context of the effect on the properties of functionalized nanotubes and their application. As a result, this will allow us to choose the optimal modification method for specific practical tasks.

Impact of Dielectric Environment on Trion Emission from Single-Walled Carbon Nanotube Networks

Trions are charged excitons that form upon optical or electrical excitation of low-dimensional semiconductors in the presence of charge carriers (holes or electrons). Trion emission from semiconducting single-walled carbon nanotubes (SWCNTs) occurs in the near-infrared and at lower energies compared to the respective exciton. It can be used as an indicator for the presence of excess charge carriers in SWCNT samples and devices. Both excitons and trions are highly sensitive to the surrounding dielectric medium of the nanotubes, having an impact on their application in optoelectronic devices. Here, the influence of different dielectric materials on exciton and trion emission from electrostatically doped networks of polymer-sorted (6,5) SWCNTs in top-gate field-effect transistors is investigated. The observed differences of trion and exciton emission energies and intensities for hole and electron accumulation cannot be explained with the polarizability or screening characteristics of the different dielectric materials, but they show a clear dependence on the charge trapping properties of the dielectrics. Charge localization (trapping of holes or electrons by the dielectric) reduces exciton quenching, emission blue-shift and trion formation. Based on the observed carrier type and dielectric material dependent variations, the ratio of trion to exciton emission and the exciton blue-shift are not suitable as quantitative metrics for doping levels of carbon nanotubes.

Hybrid, dual visible and near-infrared fluorescence emission of (6,5) single-walled carbon nanotubes modified with fluorescein through aryl diazonium salt chemistry

The aryl diazonium salt chemistry offers enhancement of near-infrared (NIR) emission of single-walled carbon nanotubes (SWCNTs), although, the attachment of functional molecules which could bring hybrid properties through the process is underdeveloped. In this work, we utilize aryl diazonium salt of fluorescein to createsp³defects on (6,5) SWCNTs. We study the influence of pH on the grafting process identifying that pH 5-6 is necessary for a successful reaction. The fluorescein-modified (6,5) SWCNTs (F-(6,5) SWCNTs) exhibit red-shiftedE₁₁* emission in the NIR region attributed to luminescentsp³defects, but also visible (Vis) fluorescence at 515 nm from surface-attached fluorescein molecules. The fluorescence in both Vis and NIR regions of F-(6,5) SWCNTs exhibit strong pH-dependency associated with the dissociation of fluorescein molecules with an indication of photoinduced-electron transfer quenching the Vis emission of fluorescein dianion. The F-(6,5) SWCNTs could potentially be used for dual-channel medical imaging as indicated by our preliminary experiments. We hope that our research will encourage new, bold modifications of SWCNTs with functional molecules introducing new, unique hybrid properties.

Azide modification forming luminescent sp2 defects on single-walled carbon nanotubes for near-infrared defect photoluminescence

Azide functionalization produced luminescent sp²-type defects on single-walled carbon nanotubes, by which defect photoluminescence appeared in near infrared regions (1116 nm). Changes in exciton properties were induced by localization effects at the defect sites, creating exciton-engineered nanomaterials based on the defect structure design.

Protein-structure-dependent spectral shifts of near-infrared photoluminescence from locally functionalized single-walled carbon nanotubes based on avidin-biotin interactions

Single-walled carbon nanotubes (SWCNTs) emit photoluminescence (PL) in the near-infrared (NIR) region (>900 nm). To enhance their PL properties, defect doping via local chemical functionalization has been developed. The locally functionalized SWCNTs (lf-SWCNTs) emit red-shifted and bright E₁₁* PL originating from the excitons localized at the defect-doped sites. Here, we observe the E₁₁* PL energy shifts induced by protein adsorption via the avidin-biotin interactions at the doped sites of lf-SWCNTs. We establish that the difference in the structures of the avidin derivatives notably influences the energy shifts. First, lf-SWCNT-tethering biotin groups (lf-SWCNTs-b) are synthesized based on diazonium chemistry, followed by post-modification. The responsiveness of the lf-SWCNTs-b to different microenvironments is investigated, and a correlation between the E₁₁* PL energy shift and the induction-polarity parameters of surrounding solvents is established. The adsorption of neutravidin onto the lf-SWCNTs-b induces an increase in the induction-polarity parameters around the biotin-doped sites, resulting in the red-shift of the E₁₁* PL peak. The E₁₁* PL shift behaviors of the lf-SWCNTs-b change noticeably when avidin and streptavidin are introduced compared to the case with neutravidin. This is due to the different microenvironments formed at the biotin-doped sites, attributed to the difference in the structural features of the introduced avidin derivatives. Moreover, we successfully enhance the detection signals of lf-SWCNTs-b (>three fold) for streptavidin detection using a fabricated film device. Therefore, lf-SWCNTs exhibit significant promise for application in advanced protein detection/recognition devices based on NIR PL.

Quantum Defects as a Toolbox for the Covalent Functionalization of Carbon Nanotubes with Peptides and Proteins

Single-walled carbon nanotubes (SWCNTs) are a 1D nanomaterial that shows fluorescence in the near-infrared (NIR, >800 nm). In the past, covalent chemistry was less explored to functionalize SWCNTs as it impairs NIR emission. However, certain sp3 defects (quantum defects) in the carbon lattice have emerged that preserve NIR fluorescence and even introduce a new, red-shifted emission peak. Here, we report on quantum defects, introduced using light-driven diazonium chemistry, that serve as anchor points for peptides and proteins. We show that maleimide anchors allow conjugation of cysteine-containing proteins such as a GFP-binding nanobody. In addition, an Fmoc-protected phenylalanine defect serves as a starting point for conjugation of visible fluorophores to create multicolor SWCNTs and in situ peptide synthesis directly on the nanotube. Therefore, these quantum defects are a versatile platform to tailor both the nanotube's photophysical properties as well as their surface chemistry.

Brightening of Long, Polymer-Wrapped Carbon Nanotubes by sp3 Functionalization in Organic Solvents

The functionalization of semiconducting single-walled carbon nanotubes (SWNTs) with sp3 defects that act as luminescent exciton traps is a powerful means to enhance their photoluminescence quantum yield (PLQY) and to add optical properties. However, the synthetic methods employed to introduce these defects are currently limited to aqueous dispersions of surfactant-coated SWNTs, often with short tube lengths, residual metallic nanotubes, and poor film-formation properties. In contrast to that, dispersions of polymer-wrapped SWNTs in organic solvents feature unrivaled purity, higher PLQY, and are easily processed into thin films for device applications. Here, we introduce a simple and scalable phase-transfer method to solubilize diazonium salts in organic nonhalogenated solvents for the controlled reaction with polymer-wrapped SWNTs to create luminescent aryl defects. Absolute PLQY measurements are applied to reliably quantify the defect-induced brightening. The optimization of defect density and trap depth results in PLQYs of up to 4% with 90% of photons emitted through the defect channel. We further reveal the strong impact of initial SWNT quality and length on the relative brightening by sp3 defects. The efficient and simple production of large quantities of defect-tailored polymer-sorted SWNTs enables aerosol-jet printing and spin-coating of thin films with bright and nearly reabsorption-free defect emission, which are desired for carbon nanotube-based near-infrared light-emitting devices.

One-Pot, Large-Scale Synthesis of Organic Color Center-Tailored Semiconducting Carbon Nanotubes

Organic color center-tailored semiconducting single-walled carbon nanotubes are a rising family of synthetic quantum emitters that display bright defect photoluminescence molecularly tunable for imaging, sensing, and quantum information processing. A major advance in this area would be the development of a high-yield synthetic route that is capable of producing these materials well exceeding the current μg/mL scale. Here, we demonstrate that adding a chlorosulfonic acid solution of raw carbon nanotubes, sodium nitrite, and an aniline derivative into water readily leads to the synthesis of organic color center-tailored nanotubes. This unexpectedly simple one-pot reaction is highly scalable (yielding hundreds of milligrams of materials in a single run), efficient (reaction completes in seconds), and versatile (achieved the synthesis of organic color centers previously unattainable). The implanted organic color centers can be easily tailored by choosing from the more than 40 aniline derivatives that are commercially available, including many fluoroaniline and aminobenzoic acid derivatives, and that are difficult to convert into diazonium salts. We found this chemistry works for all the nanotube chiralities investigated. The synthesized materials are neat solids that can be directly dispersed in either water or an organic solvent by a surfactant or polymer depending on the specific application. The nanotube products can also be further sorted into single chirality-enriched fractions with defect-specific photoluminescence that is tunable over ∼1100 to ∼1550 nm. This one-pot chemistry thus provides a highly scalable synthesis of organic color centers for many potential applications that require large quantities of materials.