Resonance Tunability and Ultra-Long Range Enhancement of Plasmon-Coupled Resonance Energy Transfer Facilitated by Silver Nanorods (I): An Overview via Computational Study

Resonance energy transfer (RET) between molecules or quantum dots is an important process in many energy related applications. Different environmental structures have been studied and demonstrated to be able to enhance the RET rate between a nearby donor-acceptor pair. In particular, cylindrical silver nanorods and nanowires have shown extraordinary ability to transfer energy along its longitudinal axis over large distances. However, the mechanism of such transfer and the exact effects on molecular RET process are yet elusive. In this study, we use the recently developed computational tool based on the plasmon-coupled resonance energy transfer (PC-RET) method to systematically study the effects of nanorods with different dimensions on RET rates. We find that highly frequency-dependent coupling factor (CF) spectra, whose amplitudes determine RET rates, can be obtained due to the localized surface plasmon polariton (LSPP) modes of the rods with nanoscale dimensions. Simple phenomenological models can be derived for the wavelengths of CF peaks in relation to the length and width of the nanorods, providing easy tunability for enhancing RET rate in specific wavelength ranges. When coupled to longer rods with mesoscale lengths, exponential decay of the CF over long donor-acceptor distances with a small decay constant is observed, leading to the possibility of long-range RET processes. Furthermore, drumhead resonance modes emerge on the flat ends of the rod when the rod's diameter reaches 300~nm, resulting in extra enhancement to RET rate compared to certain thinner rods. These findings shed new light on the mechanism of plasmonic enhancement with silver nanorods and establish design principles for how to optimally utilize these structures to manipulate RET processes for various applications.