Unconventional control of excited states of a dimer molecule by a localized light field between metal nanostructures

Abstract

We have made a theoretical study of the spatial interplay between the localized light field (LLF) and the electronic wavefunction of molecules. When the LLF has a nanoscale spatial variation comparable to a molecular wavefunction, this interplay is crucial to determine the optical response of molecular excited states. Such a condition can be realized in case that a molecule is lying in the vicinity of a metal nanogap. By using the calculation method applicable to arbitrary‐shaped samples, we demonstrate a drastic enhancement of the response electromagnetic field from an optical forbidden state whose magnitude is comparable to that from an allowed state. The obtained result indicates that we have a possibility to control the excited states of molecules by designing the LLF with metal nanostructures. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Single‐Molecule Surface‐Enhanced Raman Scattering as a Probe for Adsorption Dynamics on Metal Surfaces

“…It has been pointed out that steep field gradients comparable to the size of molecules result in a breakdown in the standard selection rules for electronic excitations [39,56]. Such a breakdown has been theoretically demonstrated for single-molecule excitations in nanogaps [57,58] and recently simulated for excitons in a metal-tipped nanorod [40]. Although changes in electronic excitation selection rules have not yet been proved experimentally, even for plasmon-active metal nanostructures [11], their contribution to the SERS process should be considered.…”

Recent progress and frontiers in the electromagnetic mechanism of surface-enhanced Raman scattering

“…This failure of the approximation of the linear function indicates the breakdown of the selection rule by the fine local electric field-gradient. This breakdown has been investigated by an observation of forbidden transition modes [44,50,[63][64][65][66][67][68][69][70][71][72][73].…”

Two-photon upconversion affected by intermolecule correlations near metallic nanostructures

“…where the localized field with spatial gradient is assumed to produce similar intensities of absorptions in both the dipole-allowed and -forbidden transitions [9][10][11] . The molecule-molecule interaction via the radiation field is written as…”

“…Especially, when metallic nanostructres are set at intervals of a few nanometers, there exists a "hot spot" near the gap region where the field intensity is enhanced up to 10 5 -fold 8 . In such a hot spot, the conventional selection rules of optical transitions are broken because of high gradient intensity of the strongly localized field [9][10][11] . In addition to the potential as the optical antenna, surface plasmon has a potential to combine an enormous capacity of photonics and a miniaturization of electronics [12][13][14] .…”