We describe the chemical creation of molecularly tunable fluorescent quantum defects in semiconducting carbon nanotubes through covalently bonded surface functional groups that are themselves nonemitting. By variation of the surface functional groups, the same carbon nanotube crystal is chemically converted to create more than 30 distinct fluorescent nanostructUres with unique near-infrared photoluminescence that is molecularly specific, systematically tunable, and significantly brighter than that of the parent semiconductor. This novel exciton-tailoring chemistry readily occurs in aqueous solution and creates functional defects on the sp2 carbon lattice with highly predictable C C bonding from virtually any iodine-containing hydrocarbon precursor. Our new ability to control nanostradture excitons through a single surface functional group opens up exciting possibilities for-postsynthesis chemical engineering of carbon nanomaterials and suggests that the-ikhOnal design and creation of a large variety of molecularly tunable quantum emitters for applications ranging from in vivo bioiniagirig and chemical sensing to room-temperature single-photon sources can now be anticipated.