Issue 24, 2024

Exciton annihilation and diffusion length in disordered multichromophoric nanoparticles

Abstract

Efficient exciton transport is the essential property of natural and synthetic light-harvesting (LH) devices. Here we investigate exciton transport properties in LH organic polymer nanoparticles (ONPs) of 40 nm diameter. The ONPs are loaded with a rhodamine B dye derivative and bulky counterion, enabling dye loadings as high as 0.3 M, while preserving fluorescence quantum yields larger than 30%. We use time-resolved fluorescence spectroscopy to monitor exciton–exciton annihilation (EEA) kinetics within the ONPs dispersed in water. We demonstrate that unlike the common practice for photoluminescence investigations of EEA, the non-uniform intensity profile of the excitation light pulse must be taken into account to analyse reliably intensity-dependent population dynamics. Alternatively, a simple confocal detection scheme is demonstrated, which enables (i) retrieving the correct value for the bimolecular EEA rate which would otherwise be underestimated by a typical factor of three, and (ii) revealing minor EEA by-products otherwise unnoticed. Considering the ONPs as homogeneous rigid solutions of weakly interacting dyes, we postulate an incoherent exciton hoping mechanism to infer a diffusion constant exceeding 0.003 cm2 s−1 and a diffusion length as large as 70 nm. This work demonstrates the success of the present ONP design strategy at engineering efficient exciton transport in disordered multichromophoric systems.

Graphical abstract: Exciton annihilation and diffusion length in disordered multichromophoric nanoparticles

Supplementary files

Article information

Article type
Paper
Submitted
22 jan 2024
Accepted
06 jun 2024
First published
08 jun 2024
This article is Open Access
Creative Commons BY license

Nanoscale, 2024,16, 11550-11563

Exciton annihilation and diffusion length in disordered multichromophoric nanoparticles

A. M. Gharbi, D. S. Biswas, O. Crégut, P. Malý, P. Didier, A. Klymchenko and J. Léonard, Nanoscale, 2024, 16, 11550 DOI: 10.1039/D4NR00325J

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