Programming sp3 Quantum Defects along Carbon Nanotubes with Halogenated DNA

Abstract

Atomic defect color centers in solid-state systems hold immense potential to advance various quantum technologies. However, the fabrication of high-quality, densely packed defects presents a significant challenge. Herein we introduce a DNA-programmable photochemical approach for creating organic color-center quantum defects on semiconducting single-walled carbon nanotubes (SWCNTs). Key to this precision defect chemistry is the strategic substitution of thymine with halogenated uracil in DNA strands that are orderly wrapped around the nanotube. Photochemical activation of the reactive uracil initiates the formation of sp³ defects along the nanotube as deep exciton traps, with a pronounced photoluminescence shift from the nanotube band gap emission (by 191 meV for (6,5)-SWCNTs). Furthermore, by altering the DNA spacers, we achieve systematic control over the defect placements along the nanotube. This method, bridging advanced molecular chemistry with quantum materials science, marks a crucial step in crafting quantum defects for critical applications in quantum information science, imaging, and sensing.

Figure 1.. Encoding the reactive sites into a DNA sequence for creating OCCs on SWCNTs.

(A) Schematic illustrating the use of engineered DNA sequences to program OCCs along a nanotube. The reactive sites (highlighted in red) are incorporated by replacing thymine (T) with halogenated uracil (5-I-dU), which is UV-cleavable to form a reactive radical with the nanotube. (B) Molecular models showing the retention of DNA ordered wrapping after covalent attachment. (C) Absorption spectra of the T(GT)₁₅ and (5-I-dU)(GT)₁₅ ssDNA-dispersed (6,5)-SWCNT samples. For clarity, the spectrum is offset. Inset shows the corresponding SWCNT solutions prior to a 33-fold dilution for the spectral measurements. (D) Cross-sectional view of the (6,5)-SWCNT@(5-I-dU)(GT)₁₅ before and after covalent bonding the dU nucleobase to the nanotube at the iodine leaving site. The bonding atoms and dU are highlighted by ball-sticks.

Figure 2.. Photochemically triggered creation of OCCs on (5-I-dU)(GT)₁₅ ssDNA-wrapped (6,5)-SWCNTs.

(A) PL excitation-emission maps of the sample before (top) and after (bottom) exposure to 254 nm UV light. (B) Raman spectra before (red) and after 3-hours of UV-irradiation (blue), measured using 532 nm excitation. (C) Photoluminescence spectra within the first 3 hours of the UV irradiation, recorded at 565 nm excitation.

Figure 3.. Controlling the defect spacing using inert DNA spacers.

(A) The PL emission-excitation maps and (B) PL spectra at 565 nm excitation of the DNA/SWCNT samples with different 5-I-dU(GT)₁₅:T(GT)₁₅ ratios after 1 hour reaction. The unmodified DNA sequence, T(GT)₁₅, serves as a spacer (depicted in gray in insets), while the modified sequence, 5-I-dU(GT)₁₅, is in red. (C, D) OCC PL images of individual SWCNTs reacted with 5-I-dU(GT)₁₅:T(GT)₁₅ at ratios of (C) 6:0 and (D) 1:5. Note these images display only OCCs, whereas the nanotube E₁₁ PL is filtered using a long pass filter.

Figure 4.. Atomic force microscopy imaging of DNA-programmed quantum defects on individual nanotubes.

AFM images of (A) control: SWCNT@(5-I-dU)(GT)₁₅, and (B, C) (6,5)-SWCNT-dU(GT)₁₅ after removal of free DNA. The DNA is visible only in the SWCNT-dU(GT)₁₅ sample where the DNA strands are covalently bonded to the nanotube surface and cannot be removed by DOC. (D) Height profile along the length of the nanotube shown in (C), which is a zoomed-in view corresponding to the marked area in (B).