Solvent effect in dynamic superstructures from au nanoparticles and cdte nanowires: Experimental observation and theoretical description

Solvent effects on luminescence in nanocolloids are typically related to changes in the dielectric constant around the light-emitting species, but they can have a completely different nature in complex dynamic nanoscale assemblies. Hybrid superstructures were assembled from Au nanoparticles (NPs) and CdTe nanowires (NWs) via poly(ethylene glycol) (PEG) bridges and provide the first example of solvent-responsive dynamic nanoscale assemblies from NWs. The photoluminescence (PL) intensity of the CdTe NWs was found to be dependent on the hydrophilic/hydrophobic balance of the solvent (water, methanol, ethanol, and 2-propanol) surrounding the superstructure and displayed slow equilibration kinetics. PL gradually decreased over a period of 2000 s by ca. 50% for ethanol and ca. 70% for 2-propanol, whereas it remained constant for water and methanol. This phenomenon was attributed to the solvent dependence of the radius of gyration (RF) of the PEG bridges between the NPs and NWs, which swells in ethanol and 2-propanol. The average distance between the NPs and NWs affects the plasmon-exciton interactions responsible for optical processes in the superstructure, and expansion results in a decrease of the luminescence enhancement of Cd Te by Au NPs. Theoretical modeling was carried out to confirm the mechanism of the solvent effect. Exciton-plasmon resonance was described as a combination of two components: field enhancement and energy transfer. Although carrying some limitations and being inherently approximate, this approach was able to describe the distance dependence of the PL intensity of NP-NW system well. The suggested theoretical model expands the understanding of plasmon-exciton electronic systems and can be applied to many semiconductor-metal superstructures.