Fluorescence intermittency originates from reclustering in two-dimensional organic semiconductors

Anthony Ruth,Masaru Kuno,Peter Zapol,Boldizsár Jankó,Yurii V Morozov,Jixin Si,Matthew P Mcdonald,Michitoshi Hayashi

doi:10.1038/ncomms14521

Abstract

Fluorescence intermittency or blinking is observed in nearly all nanoscale fluorophores. It is characterized by universal power-law distributions in on- and off-times as well as 1/f behaviour in corresponding emission power spectral densities. Blinking, previously seen in confined zero- and one-dimensional systems has recently been documented in two-dimensional reduced graphene oxide. Here we show that unexpected blinking during graphene oxide-to-reduced graphene oxide photoreduction is attributed, in large part, to the redistribution of carbon sp2 domains. This reclustering generates fluctuations in the number/size of emissive graphenic nanoclusters wherein multiscale modelling captures essential experimental aspects of reduced graphene oxide’s absorption/emission trajectories, while simultaneously connecting them to the underlying photochemistry responsible for graphene oxide’s reduction. These simulations thus establish causality between currently unexplained, long timescale emission intermittency in a quantum mechanical fluorophore and identifiable chemical reactions that ultimately lead to switching between on and off states.

Highlights

Fluorescence intermittency or blinking is observed in most nanoscale fluorophores
Graphene oxide (GO) possesses a band-gap that gives rise to strong fluorescence in the visible spectrum[16] that can be tuned by gradual reduction into reduced graphene oxide[17]
The explicit link established between emission/absorption trajectories and the structural/chemical transformation of GO/reduced graphene oxide (rGO) strongly suggests that blinking in rGO originates from reclustering—sp[2] cluster creation and destruction processes as well as processes which distort sp[2] domains in a reversible manner

Summary

Introduction

Fluorescence intermittency or blinking is observed in most nanoscale fluorophores. This reclustering generates fluctuations in the number/size of emissive graphenic nanoclusters wherein multiscale modelling captures essential experimental aspects of reduced graphene oxide’s absorption/emission trajectories, while simultaneously connecting them to the underlying photochemistry responsible for graphene oxide’s reduction These simulations establish causality between currently unexplained, long timescale emission intermittency in a quantum mechanical fluorophore and identifiable chemical reactions that lead to switching between on and off states. The agreement between simulation and experiment grows with model parameterization until new optical behaviour, fluorescence intermittency, emerges from rules governing single chemical reactions This has broader implications beyond GO/rGO blinking since despite the nearly three decades of work on the matter[22,23], the current study is the first to link blinking to a definitive chemical process. Graphenic domains are embedded within a disordered, sp3-hybridized matrix with photolytic reduction leading to GO-to-rGO interconversion through changes to the local number, size and overall density of aromatic sp[2] clusters[15,17,28]

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Results

Conclusion