Triplet Exciton Diffusion in Platinum Polyyne Films

Abstract

A time-resolved photoluminescence quenching approach is developed for determining the triplet exciton diffusion coefficient and diffusion length (D and L D , respectively) of phosphorescent conjugated polymers. This method is applied to a solid-state organometallic conjugated polymer with the structure [−Pt(PBu 3 ) 2 −CC−C 6 H 4 −CC−] n (where Bu = n-butyl and −C 6 H 4 − is 1,4-phenylene). The approach relies on analysis of the lifetime quenching of the polymer's phosphorescence by a series of three different quenchers that are dispersed into the polymer phase at varying concentration. The lifetime quenching data are analyzed by using a modified Stern−Volmer quenching expression to determine the diffusion-controlled quenching rate constant, k q , which is then related to the exciton diffusivity, D, and diffusion length, L D . The diffusion coefficients that are determined using the three quenchers are consistent, D ≈ 4 × 10 −6 cm 2 s −1 , and combined with the triplet exciton lifetime of the pristine polymer (τ = 1.05 μs) give an exciton diffusion length L D ≈ 22 nm. The results are compared to literature studies of singlet exciton diffusion in conjugated polymers and triplet exciton diffusion in molecular materials.

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“…122,123 If the material shows monoexponential PL decays, one may apply a simple Stern-Volmer analysis. 116,[195][196][197][198][199][200] These modeling approaches allow extracting the exciton diffusion coefficient typically as the only fitting parameter.…”