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Abstract

Light in the near-infrared (NIR) plays a central role in today’s telecommunications systems and biomedical research as it overlaps with the transmission window of silica fibers and biological tissues. Due to their narrowband photoluminescence (PL) in the NIR, semiconducting singlewalled carbon nanotubes (SWNTs) have emerged as a promising material for optoelectronic devices, bioimaging, and (bio)sensing. The covalent functionalization of SWNTs with luminescent defects enhances their optical properties, resulting in a bright red-shifted emission band with potential application as a quantum-light source. However, existing synthetic protocols offer little control over the creation of these defects and as a result emission occurs across a wide spectral range. For practical applications, it is crucial to reduce this spectral diversity and selectively introduce defects that exhibit the desired properties. Moreover, creating luminescent defects with high brightness is challenging and has impeded their application in bioimaging. Hence, their potential as biosensors is also largely unknown.

This thesis introduces a synthetic protocol for the selective creation of one specific type of luminescent sp3 defect in polymer-sorted (6,5) SWNTs. Compared to commonly obtained defects, this type of defect emits more red-shifted light and exhibits longer PL lifetimes. The created defects exhibit single-photon emission at room temperature and the emission can be tuned further towards telecommunication wavelengths by functionalization of other SWNTs species. This new functionalization protocol relies on a base-promoted coupling approach that primarily utilizes aniline derivatives. These aniline derivatives react through nucleophilic addition with the SWNT lattice. The functionalized SWNTs exhibit excellent solution processability, which will enable their integration into electrically-driven devices and quantum-light sources. In a second functionalization protocol, luminescent oxygen defects were created in aqueous dispersed SWNTs through reaction with reactive oxygen species produced by Fenton like copper redox chemistry. In the case of functionalized (6,5) SWNTs, a 5-fold brightening effect and a PL quantum yield of 3% was observed. The method employs benign and inexpensive chemicals and can be performed at high SWNT concentrations using commercially available unsorted raw material, enabling large-scale production. The excellent optical properties of functionalized SWNTs persist even after being made biocompatible through coating with biopolymers (e.g. DNA), making them suitable for future applications in in vivo NIR imaging or biosensing.

Finally, in a rational approach, sp3-functionalized (6,5) SWNTs were designed for the optical detection of the biomarker inorganic pyrophosphate (PPi). The detection scheme relies on a metal displacement assay, wherein copper ions reversible quench the PL of functionalized SWNTs bearing an alkyne moiety. Quenching proceeds via photo-induced electron transfer when Cu2+ ions are immobilized on the SWNT surface, facilitated by a triazole ligand and coordination to covalently attached aryl alkyne groups. PL quenching is more pronounced for defect emission, enabling the detection of PPi in ratiometric measurements. When made biocompatible by coating with phospholipid-polyethylene glycol, this sensor is suitable for detecting PPi released during DNA synthesis in polymerase chain reaction. This sensor design may serve as a starting point for the further rational design of biosensors based on SWNTs functionalized with luminescent defects.