Photochemical spin-state control of binding configuration for tailoring organic color center emission in carbon nanotubes

Switching Photoluminescence Wavelength of Arylated Single-walled Carbon Nanotubes by Utilizing Steric Hindrance in Reductive Arylation

(6,5)-enriched single-walled carbon nanotubes (SWCNTs) were reductively arylated using sodium naphthalenide and monosubstituted and disubstituted iodobenzene derivatives to control their photoluminescence (PL) properties. In the reactions with substituted iodobenzenes, the degree of functionalization was influenced by the substituents on the aryl groups depending on their position, which allowed us to realize control of the PL intensity and wavelength. The methyl or methoxy group at the 2-position and methyl groups at the 3,5-positions of the phenyl group respectively increased the E11** PL and E11* PL selectivity at ~1230 and ~1100 nm. Methyl groups at the 2,6-positions emerged two new PL peaks. These PL characteristics were prominently observed in the (6,4) SWCNT adducts, which were separated by gel chromatography. Theoretical calculations of model compounds showed that the effect of the substituent at the ortho-position on the relative stability of the isomers with different binding configurations was greater for the diarylated SWCNTs than for the hydroarylated SWCNTs. Experimental and theoretical calculation results revealed that the choice of substituents on the benzene ring was effectively used to modulate the PL wavelength, and these substituents had a considerable effect on the favorable binding configuration of the SWCNT adduct and relative stability and PL wavelength of the conformational isomers.

Isomerization of surface functionalized SWCNTs and the critical influence on photoluminescence: static calculations and excited-state dynamics simulations

Single-walled carbon nanotubes (SWCNTs) functionalized with sparse surface chemical groups are promising for a variety of optical applications such as quantum information and bio-imaging. However, the luminescence efficiencies and stability, two key aspects, undoubtedly govern their practical usage. Herein, we assess the surface migration of oxygen and triazine groups on as-modified SWCNT fragments by adopting transition state theory and explore the de-excitation of oxygen-functionalized SWCNT fragments by performing non-adiabatic excited-state dynamics simulations. According to the predicted moderate or even small reaction barriers, the migration of both oxygen and triazine groups is feasible from an sp3 defect configuration forming an energetically more stable sp2 configuration at moderate or even room temperatures. Such isomerization leads to drastically different light emission capabilities as indicated by the large or zero oscillator strengths. During the dynamics simulations, the lowest excited singlet (S1) state rapidly decays in energy within 20 fs and then fluctuates until the end, providing insights into the emission mechanism of SWCNTs. This study highlights the potential intrinsic limitations of surface-functionalized SWCNTs for luminescence applications.

Recent progress in controlling the photoluminescence properties of single-walled carbon nanotubes by oxidation and alkylation

The functionalization of single-walled carbon nanotubes (SWCNTs) has received considerable attention in the last decade since highly efficient near-infrared photoluminescence (PL) has been observed to be red-shifted compared with the intrinsic PL peak of pristine SWCNTs. The PL wavelength has been manipulated using arylation reactions with aryldiazonium salts and aryl halides. Additionally, simple oxidation and alkylation reactions have proven effective in extensively adjusting the PL wavelength, with the resulting PL efficiency varying based on the chosen reaction techniques and molecular structures. This review discusses the latest developments in tailoring the PL attributes of SWCNTs by oxidation and alkylation processes. (6,5) SWCNTs exhibit intrinsic emission at 980 nm, and the PL wavelength can be controlled in the range of 1100-1320 nm by chemical modification. In addition, recent developments in chiral separation techniques have increased our understanding of the control of the PL wavelength, extending to the selection of excitation and emission wavelengths, by chemical modification of SWCNTs with different chiral indices.

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.

Investigating Molecular Exciton Polaritons Using Ab Initio Cavity Quantum Electrodynamics

Coupling molecules to the quantized radiation field inside an optical cavity creates a set of new photon-matter hybrid states called polariton states. We combine electronic structure theory with quantum electrodynamics (QED) to investigate molecular polaritons using ab initio simulations. This framework joins unperturbed electronic adiabatic states with the Fock state basis to compute the eigenstates of the QED Hamiltonian. The key feature of this "parametrized QED" approach is that it provides the exact molecule-cavity interactions, limited by only approximations made in the electronic structure. Using time-dependent density functional theory, we demonstrated comparable accuracy with QED coupled cluster benchmark results for predicting potential energy surfaces in the ground and excited states and showed selected applications to light-harvesting and light-emitting materials. We anticipate that this framework will provide a set of general and powerful tools that enable direct ab initio simulation of exciton polaritons in molecule-cavity hybrid systems.

Signatures of Chemical Dopants in Simulated Resonance Raman Spectroscopy of Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) with organic sp2 or sp3 hybridization defects allow the robust tunability of many optoelectronic properties in these topologically interesting quasi-one-dimensional materials. Recent resonant Raman experiments have illuminated new features in the intermediate-frequency region upon functionalization that change with the degree of functionalization as well as with interactions between defect sites. In this Letter, we report ab initio simulated near-resonant Raman spectroscopy results for pristine and chemically functionalized SWCNT models and find new features concomitant with experimental observations. We are able to assign the character of these features by varying the frequency of the external Raman laser frequency near the defect-induced E11* optical transition using a perturbative treatment of the electronic structure of the system. The obtained insights establish relationships between the nanotube atomistic structure and Raman spectra facilitating further exploration of SWCNTs with tunable optical properties tuned by chemical functionalization.