Tuning of Molecular Plasmons in Anthracene by Peripheral Functionalization

A term “molecular plasmon” was recently introduced to describe collective, coherent excitations in polycyclic aromatic hydrocarbons (PAHs). In spite of significant practical implications of molecular plasmons, experimental studies demonstrating how their properties can be controlled are currently limited. Here we report first experimental study of the effect of a systematic peripheral functionalization in a series of synthesized anthracene derivatives on the energy and extent of plasmonic character of their electronic excitations. Spectroscopically observed electronic excitations in electrochemically charged anthracene derivatives are analyzed in terms of several molecular plasmonicity metrics using Time-Dependent Density Functional Theory (TDDFT). We show that the energy and the degree of plasmonicity of the electronic excitations vary systematically with the position and type of the peripheral functionalization. We explain the origin of these variations and outline how targeted functionalization can be used to tune the plasmonic response of linear PAHs.