Direct observation of ultrafast coherent exciton dynamics in helical π-stacks of self-assembled perylene bisimides.

Jooyoung Sung,Dongho Kim,Pyosang Kim,Benjamin Fimmel,Frank Würthner

doi:10.1038/ncomms9646

Jooyoung Sung, Dongho Kim + Show 3 more

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https://doi.org/10.1038/ncomms9646

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Journal: Nature Communications	Publication Date: Oct 23, 2015
Citations: 154	License type: CC BY 4.0

Affiliation: Yonsei University, University of Würzburg

Abstract

Ever since the discovery of dye self-assemblies in nature, there have been tremendous efforts to exploit biomimetic supramolecular assemblies for tailored artificial photon processing materials. This feature necessarily has resulted in an increasing demand for understanding exciton dynamics in the dye self-assemblies. In a sharp contrast with J-type aggregates, however, the detailed observation of exciton dynamics in H-type aggregates has remained challenging. In this study, as we succeed in measuring transient fluorescence from Frenkel state of π-stacked perylene tetracarboxylic acid bisimide dimer and oligomer aggregates, we present an experimental demonstration on Frenkel exciton dynamics of archetypal columnar π–π stacks of dyes. The analysis of the vibronic peak ratio of the transient fluorescence spectra reveals that unlike the simple π-stacked dimer, the photoexcitation energy in the columnar π-stacked oligomer aggregates is initially delocalized over at least three molecular units and moves coherently along the chain in tens of femtoseconds, preceding excimer formation process.

Highlights

Ever since the discovery of dye self-assemblies in nature, there have been tremendous efforts to exploit biomimetic supramolecular assemblies for tailored artificial photon processing materials
We begin by reviewing the salient features of the absorption spectra of perylene tetracarboxylic acid bisimide (PBI) 1 dimer and PBI 2 oligomer aggregates
The absorption spectra of PBI 1 were measured in the methylcyclohexane s(oMlvCenHt ))maitxtaubroeveof10CÀH2CMl3,/MwhCeHre

Summary

Introduction

Ever since the discovery of dye self-assemblies in nature, there have been tremendous efforts to exploit biomimetic supramolecular assemblies for tailored artificial photon processing materials. This feature necessarily has resulted in an increasing demand for understanding exciton dynamics in the dye self-assemblies. As we succeed in measuring transient fluorescence from Frenkel state of p-stacked perylene tetracarboxylic acid bisimide dimer and oligomer aggregates, we present an experimental demonstration on Frenkel exciton dynamics of archetypal columnar p–p stacks of dyes. Despite numerous researches, it has long been challenging to understand the exciton migration behaviour of the primarily generated exciton in p–p stacked self-assemblies of dye molecules. A comparative study on PBI dimer and the extended PBI aggregates allows us to estimate exciton localization, a process of relevance in light-harvesting systems of photosynthesis and organic electronic devices

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Results

Conclusion