Molecular Plasmonics with Tunable Exciton−Plasmon Coupling Strength in J-Aggregate Hybridized Au Nanorod Assemblies

Abstract

Controlling coherent electromagnetic interactions in molecular systems is a problem of both fundamental interest and important applicative potential in the development of photonic and opto-electronic devices. The strength of these interactions determines both the absorption and emission properties of molecules coupled to nanostructures, effectively governing the optical properties of such a composite metamaterial. Here we report on the observation of strong coupling between a plasmon supported by an assembly of oriented gold nanorods (ANR) and a molecular exciton. We show that the coupling is easily engineered and is deterministic as both spatial and spectral overlap between the plasmonic structure and molecular aggregates are controlled. We think that these results in conjunction with the flexible geometry of the ANR are of potential significance to the development of plasmonic molecular devices.

Strong coupling in molecular exciton-plasmon Au nanorod array systems

“…J-aggregate samples were prepared using meso-tetra (n-methyl-4-pyridyl) porphyrine tetra chloride (Frontier scientific) at pH=1 inducing J-aggregate formation by drop deposition as per reported procedures [19][20][21]. Reflection spectra from the nanorod array were measured in TE and TM polarizations and showed two broad bands associated with transverse and longitudinal modes from the nanorod array which are in line with literature reports (as shown in Figure 1(b)) [3,4,18]. Reflection spectra were recorded for the J-aggregate/nanorod sample as a function of (ΔR/R = (R sample − R background )/R background ) using a gold mirror background reference.…”

“…Strong coupling between plasmons on oriented gold nanorods arrays and J-aggregate molecular exciton has been demonstrated using a series of arrays with different architectures to control the spatial and spectral overlap between the plasmonic structure and exciton molecular aggregates [18]. Here we demonstrate tuning/detuning of strong coupling in self-standing nanorod arrays achieved though angular tuning.…”

“…Tuning of plasmon-exciton coupling strength has been reported for strongly coupled exciton-plasmon states in Au nanodisk arrays coated with J-aggregate molecules achieved by changing the incident angle of incoming light, rather than changing the geometry 2 of the plasmonic nanomaterial. Using such an angle resolved approach plasmon-exciton coupling of variable strengths was achieved [17].Strong coupling between plasmons on oriented gold nanorods arrays and J-aggregate molecular exciton has been demonstrated using a series of arrays with different architectures to control the spatial and spectral overlap between the plasmonic structure and exciton molecular aggregates [18]. Here we demonstrate tuning/detuning of strong coupling in self-standing nanorod arrays achieved though angular tuning.…”

“…SEM studies (using a Jeol 6500F field emission SEM) reported that the Au nanorod substrate possesses a 70 ± 11 nm array period (center to center distance), a rod diameter 35 nm ± 7 and rod height of 200 ± 25 nm. The nanorods are encased in an anodic aluminum oxide (AAO) template which was removed prior to sample preparation via an etching solution in 30 mM NaOH as reported previously [3,4,18]. J-aggregate samples were prepared using meso-tetra (n-methyl-4-pyridyl) porphyrine tetra chloride (Frontier scientific) at pH=1 inducing J-aggregate formation by drop deposition as per reported procedures [19][20][21].…”

Mode Modification of Plasmonic Gap Resonances Induced by Strong Coupling with Molecular Excitons

“…Specifically, plasmonic cavities are specially designed metallic nanostructures, in which collective oscillation of conduction electrons, known as localized surface plasmons, can be excited upon illumination. The interaction between plasmonic resonances and nearby atomic or molecular excitons gives rise to so called plexcitonic coupling [16].For convenience of measurements, previous experiments exploring plexcitonic coupling were primarily based on ensemble metallic nanostructures, including arrays of nanovoids [17,18] or nanoparticles (NPs) [19][20][21][22][23] and nanocrystals in solution [16,[24][25][26]. Recently several groups have 3 moved to a much smaller scale, investigating strong interaction of molecular excitons with individual plasmonic resonators, such as metallic nanospheres [27,28], nanorods [29][30][31], nanoprisms [15] and nanodisk dimers [13].…”