Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 19, Issue 14, Pages 9478-9484Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c7cp00094d
Keywords
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Funding
- CONICET
- UNQ
- ANPCyT [PICT-2014-2662]
- Los Alamos National Laboratory (LANL) Directed Research and Development Funds
- National Nuclear Security Administration of the U.S. Department of Energy [DE-AC52-06NA25396]
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In the last decade, recent synthetic advances have launched carbon-based pi-conjugated hoops to the forefront of theoretical and experimental investigation not only for their potential use as bottom-up templates for carbon nanotube (CNT) growth, but also for the interesting excitonic effects arising from the cyclic geometry, unique pi-system orientation, and unusual electronic interactions and couplings. In particular, cyclic materials based on pyrene, a common component in organic electronics, are popular candidates for the future design of pi-conjugated nanorings for optoelectronic applications. Understanding the photophysical response in cyclic oligopyrenes can be achieved using non-adiabatic excited state molecular dynamics (NA-ESMD). Through NA-ESMD modeling, we reveal details of the nonradiative relaxation processes in the circular pyrene tetramer [4] cyclo-2,7-pyrenylene ([4]CPY) where we find that the strong non-adiabatic coupling combined with the dense manifold of excited states creates an internal conversion mechanism dominated by ultrafast sequential quantum transitions. However, we observe two long-lived electronic excited states that introduce a phonon bottleneck in the electronic relaxation process. In fact, the timescale for the electronic relaxation is almost exclusively dominated by the lifetimes of the long-lived states. We find that the states associated with the phonon bottleneck are separated from lower energy states by large energy gaps and are characterized by localization on a single pyrene unit resulting in a spatial mismatch with strongly delocalized neighboring states.
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