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.
Bibliographical noteFunding Information:
This work at Yonsei was financially supported by the Global Frontier R&D Program on Center for Multiscale Energy System (NRF-2014M3A6A7060583) funded by the National Research Foundation under the Ministry of Science, ICT & Future, Korea, and Midcareer Researcher (NRF-2005-0093839) Programs of National Research Foundation (NRF) grant funded by the Ministry of Science, ICT & Future, Korea. This work at the Würzburg was financially supported by the DFG (project Wu 317/15 within research unit 1809 on ‘Light induced dynamics in molecular aggregates’ at the Universität Würzburg). We thank C. Simon and J. Bialas (the Universität Würzburg) for synthesizing PBI 1 and PBI 2 molecules.
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)
- Physics and Astronomy(all)