Fluorescent quantum defects are emerging as a new frontier in nanoscience. In semiconducting single-walled carbon nanotubes (SWCNTs) these symmetry-breaking defects are introduced into the sp2 carbon lattice, generating localized trap states for excitons. The emission from these states, which we call defect photoluminescence (PL), is only observed at very low defect densities, making precise control of the chemistry used to generate the defects imperative. In this dissertation I address the chemistry related to the generation of these defects in semiconducting SWCNTs. Typically, the organic reactions used to covalently modify SWCNTs are slow and imprecise, such as in the case of aryldiazonium chemistry. We use visible light that is tuned into resonance with SWCNTs to drive their functionalization by aryldiazonium salts and generate bright defect PL, accelerating the reaction and significantly improving the efficiency of covalent bonding to SWCNTs. We further expand this optical technique to another chemistry with which we demonstrate tunable switching between the inactive and reactive isomers of a diazoether compound, for highly controllable modification of nanostructures. This technique is used to selectively functionalize a SWCNT chirality within a mixture, to the near exclusion of other chiralities, even among semiconductors that are nearly identical in diameter and electronic structure. Furthermore, we address the challenge of PL self-quenching in highly concentrated systems of carbon nanomaterials, which occurs fundamentally due to the spectral overlap in their emission and absorption spectra. We demonstrate that fluorescent quantum defects extend the PL-concentration linearity over a significantly wider range than their unmodified counterparts. This optical technique and chemistry provide opportunities to chemically tailor SWCNTs at the single chirality level for improved separations, passivation, and lithography, and for generation of bright defect PL, even within highly concentrated systems