The paper studies the molecular-level active control of localized surface plasmon resonances (LSPRs) of Au nanodisk arrays with molecular machines. Two types of molecular machines - azobenzene and rotaxane - have been demonstrated to enable the reversible tuning of the LSPRs via the controlled mechanical movements. Azobenzene molecules have the property of trans-cis photoisomerization and enable the photo-induced nematic (N)-isotropic (I) phase transition of the liquid crystals (LCs) that contain the molecules as dopant. The phase transition of the azobenzene-doped LCs causes the refractive-index difference of the LCs, resulting in the reversible peak shift of the LSPRs of the embedded Au nanodisks due to the sensitivity of the LSPRs to the disks' surroundings' refractive index. Au nanodisk array, coated with rotaxanes, switches its LSPRs reversibly when it is exposed to chemical oxidants and reductants alternatively. The correlation between the peak shift of the LSPRs and the chemically driven mechanical movement of rotaxanes is supported by control experiments and a time-dependent density functional theory (TDDFT)-based, microscopic model.
Zheng YB, Yang Y-W, Jensen L, Fang L, Juluri BK, et al. (2009) Molecular active plasmonics: controlling plasmon resonances with molecular machines. Plasmonics: Nanoimaging, Nanofabrication, and their Applications V. Available: http://dx.doi.org/10.1117/12.824525.
We thank Dr. Vincent Hsiao for his contribution to the experimental part of the azobenzene-based active tuning of the localized surface plasmon resonances, Dr. Amanda J. Haes for the MATHCAD code used in the Kramers−Kronig analysis, and Dr. Vincent Crespi for helpful discussions. This research was supported by the Air Force Office of Scientific Research (AFOSR), the National Science Foundation (NSF), and the Penn State Center for Nanoscale Science (an NSF-funded MRSEC). Components of this work were conducted at the Pennsylvania State University node of the NSF-funded National Nanotechnology Infrastructure Network. One of the authors (Y.B.Z.) thanks the support of a KAUST Scholar Award and the Founder’s Prize and Grant of the American Academy of Mechanics.