Exciton localization in J-aggregates

In many cases the absorption and luminescence properties of J-aggregates are well described within the one-dimensional Frenkel exciton model for a rigid chain with static disorder. But, the chain could be deformable and if the constant of exciton-lattice coupling is strong enough, the exciton can create a chain distortion that produces a new polaronic state below the exciton band bottom. This phenomenon is called self-trapping. The self-trapping pattern of the exciton interacting with a lattice via short-range potential depends strongly on the exciton motion dimension. According to the Rashba-Toyozava theory, the excitons characterized by one-dimensional motion are always self-trapped. So, free excitons are unstable irrespective of the magnitude of exciton-lattice coupling and there is no any energy barrier which separates free and self-trapped exciton states. The spatial extension of self-trapped exciton decreases as the exciton-lattice coupling increases. The statements mentioned above were confirmed in numerous theoretical works.

Our results:
Analysis of the experimental data on low temperature selective spectroscopy and single J-aggregate spectroscopy has disclosed a hierarchy of exciton states existent within the J-aggregate band and formed during the excited state relaxation. For J-aggregates, which are characterized by a significant static disorder, strongly localized excitons have been found at the long-wavelength edge of the absorption band. They reveal a discrete energy spectrum, jump mobility and do not undergo strong relaxation. Delocalized (space extended) excitons are excited within the whole absorption band except its long-wavelength edge. They are characterized by coherent exciton transport and are the source of self-trapped excitons.

Main publications:
• A.N. Lebedenko, R.S. Grynyov, G.Ya. Guralchuk, A.V. Sorokin, S.L. Yefimova, Y.V. Malyukin. Coherent Mechanism of Exciton Transport in Disordered J-Aggregates// J. Phys. Chem. C. – 2009 – v. 113, № 29. – P. 12883–12887. abstract

• Erwin Lang, Alexander Sorokin, Markus Drechsler, Yuri V. Malyukin and Jurgen Kohler. Optical Spectroscopy on Individual amphi-PIC J-aggregates // Nano Letters. – 2005. – v.5, №12. – P.2635-2640. abstract

• G.S. Katrich, K. Kemnitz, Yu.V. Malyukin, A.M.Ratner. Distinctive features of exciton self-trapping in quasi-one-dimensional molecular chains (J-aggregates)// Journal of Luminescence.– 2000.– v.90.– P.55-71. abstract

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