Plexciton dynamics: exciton-plasmon coupling in a J-aggregate-Au nanoshell complex provides a mechanism for nonlinearity.

Coherently coupled plasmons and excitons give rise to new optical excitations-plexcitons - due to the strong coupling of these two oscillator systenfis. Time resolved studies ofJ-aggregate-Au nanoshell complexes when the nanoshell plasmon and yaggregate exciton energies are degenerate probe the dynamical behavior of this coupled system. Transient absorption of the interacting plasmon-exciton system is observed, in dramatic contrast to the photoinduced transmission of the pristine J-aggregate. An additional, transient Fano-shaped modulation within the Fano dip is also observable. The behavior of the J-aggregate-Au nanoshell complex is described by a combined one:exciton and two-exciton state model coupled to the nanoshell plasrnon.