Reverse Micelles as Architects of Selective and Enhanced Energy Transfer in Perovskite-Dye Hybrids

Harnessing excitonic energy via Förster resonance energy transfer (FRET) in nanocrystal-dye assemblies is essential for advancing light-harvesting materials. However, direct donor-acceptor contact often promotes competing electron transfer, limiting energy transfer efficiency. Here, reverse micelles are introduced as nanoreactors to spatially decouple Rhodamine B isothiocyanate (RITC) from CsPbBr₃ (CPB) nanocrystals, enabling efficient and selective energy transfer. By tuning the water-to-surfactant molar ratio (R), the spatial arrangement and microenvironment of the donor-acceptor pair within the micelles are systematically controlled. At low R values (R = 2-4), where water predominantly localizes at the interface, FRET is significantly enhanced, aided by nanoscale confinement, restricted dye orientation, and a high local dielectric constant, while suppressing electron transfer. Time-resolved photoluminescence reveals dual rise-time components, signifying FRET from both the micellar interface and aqueous core. At higher R (R = 6), micelle fusion induces water leakage, leading to CsBr stripping from CPB surfaces and transformation into non-emissive CsPb₂Br₅, thereby quenching FRET. The distinct excited state interactions are further investigated in depth via transient absorption spectroscopy measurements. This study establishes reverse micelles as tunable nanoreactors that regulate spatial confinement and interfacial coupling, offering a new paradigm for designing hybrid nanostructures with controllable energy transfer dynamics for optoelectronic and photonic applications.