The unusual fluorescence intensity enhancement of poly(p-phenyleneethynylene) polymer separated from the silver nanocube surface by H-bonded LbL shells

Abstract

The fluorescence intensity of poly(p-phenyleneethynylene) (PPE) polymer separated from the surface of plasmonic silver nanocubes (47 nm AgNCs) is measured by varying the number of layers of polyvinyl pyrrolidone (PVPON) and polymethyl acrylic acid (PMAA), n. The shell thickness is sensitive to the solvent due to the formation of a solvent-sensitive hydrogen bonding network. The fluorescent behavior of the PPE on the core–shell PPE-(PVPON-PMAA)_n–AgNCs structures fabricated here was evaluated as a function of n as well as the nature of the surrounding solvent. Surprisingly, the fluorescence intensity of the outer PPE shell is found to increase dramatically (by more than an order of magnitude) as its separation from the nanoparticle surface increases and then decreases at a distance that depends upon the swelling behavior of the polymer shells. The distance for the highest fluorescence enhancement was found to be 20.0 nm and 24.0 nm, in water and ethanol respectively. The observed change in the fluorescence intensity of the PPE polymer with increasing its separation from the plasmonic surface is proposed to result from the interplay between a short range quenching mechanism and a relatively long-range plasmonic fluorescence enhancing mechanism. DDA calculations gave support to the significant contribution of the latter mechanism.