Lifetime Characterization of Molecular Plasmons
Chapkin, Kyle David
Halas, Naomi J
Master of Science
Recent theoretical and experimental work has shown that polycyclic aromatic hydrocarbons (PAHs), a sub-nanometer, hydrogen passivated graphene-like system, can support a collective electron resonance, like a plasmon, with the addition or removal of at least a single electron. Here we more directly probe the plasmonic nature of these systems by taking excited state lifetime measurements of three molecular plasmon systems: the anion states of anthanthrene, benzo[ghi]perylene, and perylene. These systems exhibit, at minimum, bi-exponential ultrafast decay dynamics, both on picosecond timescales (orders of magnitude faster than typical single electron molecular excitations). The two components of the decay are attributed to the molecular plasmon dephasing and the vibrational relaxation of the molecule. One candidate, benzo[ghi]perylene, also exhibits an incomplete ground state recovery, shown to be a long-term lifetime, and attributed to lower excited state fluorescence. In total, this work explores the ultrafast dynamics of the molecular plasmon system and illuminates the distinction of molecular plasmons from single excitation systems, and emphasizes their similarity to other plasmonic materials, like metals and graphene.
molecular plasmon; plasmonics; lifetime; PAH