Determining Proton Diffusion in Polymer Films by Lifetimes of Luminescent Complexes Measured in the Frequency Domain

Abstract

Polymer-supported luminescent metal complexes represent an important class of oxygen, pH, and ion sensors. The diffusion properties of the analyte into the sensing film are important for rational sensor and support design and development. We describe a technique using lifetime measurements in the frequency domain for determining the diffusion coefficient of hydrochloric acid through various polymeric pH sensor films. Two types of polymers are doped with [Ru(4,7-diphenyl-1,10-phenanthroline)2(4,4'-dicarboxy-2,2'-bipyridine)]Cl2. We monitor the phase shift of luminescence (from which we calculate the apparent lifetime, tau(app)) versus time after applying a step increase in the aqueous HCl concentration at the surfaces of the film. We model the decrease in tau(app) as a function of time using the diffusion coefficient of HCl in the polymer as the only adjustable parameter. The model accurately predicts the lifetime versus time curves, and the resulting diffusion coefficients are highly dependent on the polymer. Relative to bulk water, diffusion of protons within very hydrophilic hydrated D4 polymer (a polyethylene oxide cross-linked siloxane ring polymer) films is hindered approximately 4-fold, while within a more hydrophobic sol gel it is hindered by over 1 order of magnitude. The methodology is adaptable for measuring diffusion coefficients of a variety of analytes in different sensor films as long as the bound and unbound forms luminescence and the excited states have different lifetimes.

Highly Stable Near-Unity Photoluminescence Yield in Monolayer MoS2 by Fluoropolymer Encapsulation and Superacid Treatment

“…We constructed a simple model for the process as follows. First, based on other studies which discussed the diffusion kinetics regarding TFSI or polymer film, − the diffusion of TFSI through CYTOP satisfies the criterion of Fickian diffusion. It is assumed that the swelling effect of the CYTOP film by the solvent is negligible, allowing the concentration of TFSI c ( x , t ) to be described as where x is the distance from the interface between the bulk solution and the surface of the CYTOP, t is diffusion time, D is the TFSI diffusion coefficient in CYTOP, and c s is the TFSI concentration at the interface between the bulk solution and the surface of the CYTOP ( x = 0).…”

Molecular Fluorescence, Phosphorescence, and Chemiluminescence Spectrometry

“…Aggregation was traced in the solid state as well as in solvents such as toluene, tetrahydrofuran (THF), THF and methanol, or THF and water. Bowyer et al described a technique, using lifetime measurements in the frequency domain, for determining the diffusion coefficient of hydrochloric acid through various polymeric pH sensor films (200). Bright and co-workers investigated template formation of xerogels by mesoporous matrixes by following the photophysics of two models when dissolved in solution and when sequestered within a xerogel (201).…”

“…Polymer-supported luminescent metal complexes represent an important class of oxygen, pH, and ion sensors. Proton diffusion in polymer films was studied by measuring lifetimes of luminescent complexes measured in the frequency domain (320). Molecular and mesoscale dynamics of the chromophore using timecorrelated single photon counting (TCSPC) was used to measure rotational diffusion dynamics in lipid vesicles.…”

2D luminescence imaging of pH in vivo

“…Recently, luminescence-based methods for pH measurement have been developed (7,8). However, a method for in vivo studies on human subjects has not yet been realized.…”