Engineering the Aggregation of Dyes on Ligand-Shell Protected Gold Nanoparticles to Promote Plexcitons Formation

Abstract

The ability to control the light–matter interaction in nanosystems is a major challenge in the field of innovative photonics applications. In this framework, plexcitons are promising hybrid light–matter states arising from the strong coupling between plasmonic and excitonic materials. However, strategies to precisely control the formation of plexcitons and to modulate the coupling between the plasmonic and molecular moieties are still poorly explored. In this work, the attention is focused on suspensions of hybrid nanosystems prepared by coupling cationic gold nanoparticles to tetraphenyl porphyrins in different aggregation states. The role of crucial parameters such as the dimension of nanoparticles, the pH of the solution, and the ratio between the nanoparticles and dye concentration was systematically investigated. A variety of structures and coupling regimes were obtained. The rationalization of the results allowed for the suggestion of important guidelines towards the control of plexcitonic systems.

Ultrafast Dynamics of Multiple Plexcitons in Colloidal Nanomaterials: The Mediating Action of Plasmon Resonances and Dark States

“…Among polaritonic media, the class of colloidal plexcitonic materials is particularly appealing nowadays because these materials are cheap and easy to characterize, and their synthesis is easy to scale up. 8 , 21 , 22 …”

“… 9 The peculiarity of these systems is that two different sets of resonances can be achieved either in the porphyrin’s B-band region, exploiting the strong coupling of the NPs’ plasmon with the B-band of J-aggregates, or in the Q-band region, forming plasmonic nanogaps with the monomeric species in the intermediate coupling regime. 22 By acting on the supramolecular interactions regulating the nanohybrid formation, it is possible to build systems where none, one, or both sets of resonances are present. When both plexciton resonances are simultaneously activated in the system, evidence for a plexciton relaxation cascade has been found in static photoluminescence experiments.…”

“…Plexcitons are a specific example of polaritonic states arising from the coupling of the plasmon resonance of a metal nanostructure such as a nanoparticle or a nanostructured metal surface and a molecular excitation. , Despite having higher dissipation rates than optical microcavities, metallic nanostructures allow tight confinement of the electromagnetic field of light in sub-wavelength regions, featuring extremely confined mode volumes and enabling the establishment of effective interactions with other photonic elements in close proximity. Among polaritonic media, the class of colloidal plexcitonic materials is particularly appealing nowadays because these materials are cheap and easy to characterize, and their synthesis is easy to scale up. ,, …”

“…In a previous publication, we characterized the photophysical properties of colloidal multiplexcitonic materials prepared by assembling gold spherical nanoparticles (NPs) and a tetra-sulfonate-phenyl-porphyrin (TPPS) in different aggregation states . The peculiarity of these systems is that two different sets of resonances can be achieved either in the porphyrin’s B-band region, exploiting the strong coupling of the NPs’ plasmon with the B-band of J-aggregates, or in the Q-band region, forming plasmonic nanogaps with the monomeric species in the intermediate coupling regime . By acting on the supramolecular interactions regulating the nanohybrid formation, it is possible to build systems where none, one, or both sets of resonances are present.…”

“…Among polaritonic media, the class of colloidal plexcitonic materials is particularly appealing nowadays because these materials are cheap and easy to characterize, and their synthesis is easy to scale up. 8,21,22 In a previous publication, we characterized the photophysical properties of colloidal multiplexcitonic materials prepared by assembling gold spherical nanoparticles (NPs) and a tetra-sulfonate-phenyl-porphyrin (TPPS) in different aggregation states. 9 The peculiarity of these systems is that two different sets of resonances can be achieved either in the porphyrin's B-band region, exploiting the strong coupling of the NPs' plasmon with the B-band of J-aggregates, or in the Qband region, forming plasmonic nanogaps with the monomeric species in the intermediate coupling regime.…”