Nanoplasmonics and surface enhanced spectroscopy

Effect of exciton-plasmon interaction on the exciton self-trapping in molecular aggregates

A.V. Sorokin, I.Yu. Ropakova, I.I. Bespalova, S.L. Yefimova, Yu.V. Malyukin
Institute for Scintillation Materials of NAS of Ukraine,
60 Nauky ave., 61072 Kharkiv, Ukraine, e-mail: sorokin@isma.kharkov.ua

Molecular aggregates, called J-aggregates, are well-ordered luminescent organic nanoclusters of non-covalently coupled luminophores such as cyanines, porphyrines and some other dyes. High degree of dye molecules ordering in J-aggregate’s chains results the electronic excitations delocalization and Frenkel exciton formation. Due to excitonic nature of electronic excitations, J-aggregates reveal a number of unique spectral properties such as very narrow for organic molecules spectral lines, large extinction coefficients, giant third-order optical nonlinearities and so on. Such optical properties allow considering the J-aggregates as a very promising objects for many applications. However, low photostability in solutions resulting in photodegradation and photo-reorganization processes is a considerable disadvantage of J-aggregates. One of the ways to overcome this problem is using solid samples of J-aggregates especially in the form of polymer films suitable for many applications. Unfortunately, this way often causes a significant decrease in J-aggregate luminescence quantum yield.
It was found that one of the reason of the quantum yield decrease is the exciton self-trapping due to strong exciton-phonon interaction caused by disordered polymer environment of the J-aggregates [1]. Also, we revealed that the J-aggregate interaction with plasmon resonances of metal nanoparticles could result in 8-fold luminescence enhancement for pseudoisocyanine (PIC) J-aggregates in the layered polymer films [2]. 
However, up to now it wasn’t understood how exciton-plasmon interaction influence on the exciton self-trapping. In present study, we report the exciton self-trapping suppression in PIC J-aggregates by exciton-plasmon interaction. Different reasons of such effect are discussed.
 
1.	Sorokin A.V., Pereverzev N.V., Grankina I.I., Yefimova S.L., Malyukin Yu.V. Evidence of Exciton Self-trapping in Pseudoisocyanine J-aggregates Formed in Layered Polymer Films // J Phys Chem C.-2015.-119, № 49.-P. 27865-27873.
2.	Sorokin A.V., Zabolotskii A.A., Pereverzev N.V., Bespalova I.I., Yefimova S.L., Malyukin Yu.V., Plekhanov A.I. Metal-Enhanced Fluorescence of Pseudoisocyanine J-aggregates Formed in Layer-by-Layer Assemblied Films // J Phys Chem C.-2015.-119, № 5.-P. 2743-2751.