Features of Plasmon Enhancement of Fluorescence in the Case of Molecular Aggregates
Alexander Sorokin a, Irina Grankina a, Irina Bespalova a, Svetlana Yefimova a
a Institute for Scintillation Materials of NAS of Ukraine, 60 Nauky Ave., Kharkiv, Ukraine
Proceedings of nanoGe Fall Meeting 2021 (NFM21)
#LightMatter21. Light-Matter Interactions: From Fundamental Spectroscopy to Materials Design
Online, Spain, 2021 October 18th - 22nd
Organizers: Linn Leppert and Marina Filip
Poster, Alexander Sorokin, 266
Publication date: 23rd September 2021

Supramolecular high-ordered assemblies, called J-aggregates, possess many unique spectral properties, which distinctly differ from those of the individual molecules: a narrow absorption band, near-resonant fluorescence, high oscillator strength, giant third-order susceptibility, effective resonant energy migration, etc. The specificity of J-aggregates optical properties is governed by the electronic excitations delocalized over molecular chains and molecular (Frenkel) excitons formation due to translational symmetry and strong dipole-dipole interaction between molecules in the J-aggregate chain. One of the J-aggregate characteristic features is the narrow red-shifted exciton band, called J-band with the width determined by the exciton coherence (or delocalization) length.

Unique spectral properties make J-aggregates excellent candidates for novel photonic materials especially in the form of thin films, particularly, polymer films. Indeed, while in solutions J-aggregates often possess low photostability, in polymer films their stability becomes much higher. However, J-aggregate formation in polymer films reveals also some drawbacks, such as the low fluorescence quantum yield of formed J-aggregates. One of the ways to manipulate J-aggregates optical properties in solid samples is using an effect of exciton-plasmon coupling via aggregates interaction with noble metal nanostructures.

Indeed, the J-aggregates fluorescence quantum yield enhancement can be achieved by placing the J-aggregates at the optimal distance from metal nanoparticles, i.e. in the weak regime of exciton-plasmon coupling. Particularly, for pseudoisocyanine J-aggregates in layered polymer films 8-fold fluorescence enhancement was achieved at a 16 nm distance between gold nanoparticles and the J-aggregates [1].

One of the non-radiative relaxation channels in J-aggregates is the exciton self-trapping. The latter appeared to be efficient enough for J-aggregates formed in polymer films due to increased exciton-phonon coupling [2]. It was revealed that the exciton-plasmon coupling leads to the exciton coherence length increasing due to an effect of the absorption cross-section enhancement [3]. It results in the weakening exciton-phonon coupling which in its turn, leads to the exciton self-trapping suppression. The latter enhances the J-aggregate fluorescence additionally to the direct plasmon fluorescence enhancement [3].

So, the exciton-plasmon interaction in the weak coupling regime enhances the J-aggregates fluorescence in two ways: directly by plasmon fluorescence enhancement effect and indirectly by the exciton self-trapping suppression.

© Fundació Scito
We use our own and third party cookies for analysing and measuring usage of our website to improve our services. If you continue browsing, we consider accepting its use. You can check our Cookies Policy in which you will also find how to configure your web browser for the use of cookies. More info