Red-shifted emitting states in carbon nanotubes, introduced by chemically stable and tunable covalently-bound dopants,^1,2 are gaining attention for their potential to boost photoluminescence quantum yields,^1,2 add new functionality,^3,4 and serve as single photon emitters.⁵ These sites present a rich array of new photophysics, with dependences on specific functionalization chemistry and environmental interactions. As examples, we will present low-T photoluminescence (PL) probes of defect-state electronic structure for sp³ defects introduced by aryl functionalization and compare to quantum chemical theory and to earlier studies on oxygen-introduced defects.⁶ Environmental effects on both low-T spectroscopy and ensemble-level relaxation dynamics⁷ will also be presented. In particular, dielectric environment is found to significantly impact PL relaxation times in contrasting ways, enabling further understanding of relaxation mechanisms and how they relate to spectroscopic observables. Finally, control over chemical functionality and dielectric environment will be shown as routes for optimizing single photon emission behaviors, in agreement with earlier theoretical results.⁸

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