New Methods for Investigating the Interplay of Photoluminescence Intermittency and Local Dielectric Constant

Abstract

New experimental and data analysis methods for investigating the influence of local environment on the photoluminescence intermittency (PI) or "blinking" exhibited by single luminophores are presented. Specifically, the relationship between PI and local dielectric constant for nile red (NR) embedded in poly(vinylidene fluoride) (PVDF) is determined using these new methods. Experimentally, quasi-single molecule (SM) microscopy is used to spatially resolve the distribution of dielectric constants in polymer films. By measuring the solvatochromic emission from NR, a direct correlation between the emission maximum and dielectric constant is established and used to measure the spatial varaition in dielectric constants for PVDF. The effect of sample annealing is explored, with non-annealed films exhibiting much larger dielectric constant distributions in comparison to annealed films. In addition, a decrease in the average dielectric constant with annealing time is observed and attributed to a phase transformation of PVDF from gamma- to beta-phase. New data analysis methods employing cumulative distribution functions (CDFs) are also presented. These techniques allow for the statistical analysis of PI without first assuming a parametric form for the underlying probability distribution function (PDF) describing the duration of emissive and non-emissive events. For NR in PVDF, changes in PI with variation in dielectric constant are observed and shown to be consistent with a photoinduced electron transfer mechanism. The experimental and analytical methods outlined here should prove useful in SM studies of guest-host materials designed to elucidate the role of host environment on PI exhibited by the guest luminophore.