Probing Light-Matter Interactions: Fluorescence Lifetime Manipulation in a Crystalline Colloidal Array

The connection between a structured environment and the decay kinetics of an embedded emitter is explored by copolymerizing a naphthalimide derivative within polystyrene-based nanoparticles. The nanoparticles spontaneously self-assemble into a crystalline colloidal array, resulting in a partial photonic bandgap, or rejection wavelength, in the visible regime. The rejection wavelength of the liquid ordered array can be shifted across the emission spectrum of the nanoparticles by dilution with deionized water, which increases the interparticle spacing of the array. Time-resolved fluorescence of the ordered array at various rejection wavelength conditions is monitored at high- and low-energy electronic transition frequencies across the emission spectrum of the naphthalimide-copolymerized nanoparticles. Careful attention is given to the reference systems that are used to quantify photonic effects, the wavelengths at which decay kinetics are monitored, and the quantum yield of the naphthalimide-derived emitter. Increased and decreased excited-state lifetimes are observed, depending on the position of the rejection wavelength in relation to the emission of the emitter and the monitored wavelength, revealing critical insights in the context of quantum light-matter interactions and opportunities for strategic control over emitter decay pathways.