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Contributed by Naomi J. Halas, July 24, 2018 (sent for review March 28, 2018; reviewed by Christine M. Aikens and Dmitri N. Basov)
Significance
In this work, we study collective electronic excitations—plasmons—in the few-atom limit in charged polycyclic aromatic hydrocarbon (PAH) molecules. These systems are the zero-dimensional limit of graphene, consisting of only a few fused aromatic carbon rings where the perimeter atoms are bonded to hydrogen. As systems identified as supporting plasmons, established by the transfer of a single electron to or from the neutral PAH molecule, they are perhaps the most optimal examples where a clear distinction between plasmons and single electron–hole pair excitations can be rigorously made. Here, we study the lifetime dynamics of charged versus neutral PAH molecules to characterize the relaxation channels in these quantum plasmon systems.
Abstract
Polycyclic aromatic hydrocarbon (PAH) molecules are essentially graphene in the subnanometer limit, typically consisting of 50 or fewer atoms. With the addition or removal of a single electron, these molecules can support molecular plasmon (collective) resonances in the visible region of the spectrum. Here, we probe the plasmon dynamics in these quantum systems by measuring the excited-state lifetime of three negatively charged PAH molecules: anthanthrene, benzo[ghi]perylene, and perylene. In contrast to the molecules in their neutral state, these three systems exhibit far more rapid decay dynamics due to the deexcitation of multiple electron–hole pairs through molecular plasmon “dephasing” and vibrational relaxation. This study provides a look into the distinction between collective and single-electron excitation dynamics in the purely quantum limit and introduces a conceptual framework with which to visualize molecular plasmon decay.
Footnotes
- ↵1To whom correspondence should be addressed. Email: halas{at}rice.edu.
Author contributions: P.N. and N. J. Halas designed research; K.D.C., L.B., G.J.S., A.L., N. J. Hogan, and Y.C. performed research; K.D.C., L.B., and N. J. Hogan analyzed data; and K.D.C., L.B., P.N., and N. J. Halas wrote the paper.
Reviewers: C.M.A., Kansas State University; and D.N.B., Columbia University.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1805357115/-/DCSupplemental.
Published under the PNAS license.
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Lifetime dynamics of plasmons in the few-atom limit
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