Schematic of a photoinduced electron transfer reaction between the J-aggregate and Ag nanoparticle following photoexcitation of the plasmon
Researchers in the Chemistry Division at Argonne National Laboratory have recently studied the unusual photochemistry of molecular J-aggregates on the surface of noble metal nanoparticles. Noble metal nanoparticles are known for free electron waves, or plasmons, that produce extraordinarily intense and confined electromagnetic waves within a few nanometers of the particles’ surfaces. By using molecular J-aggregates, known for their high absorption cross sections, a uniform monolayer of organic electron donors was placed on the surface of the nanoparticles. Ultrafast optical spectroscopy studies revealed a multi-electron, photoinduced reduction of the nanoparticles by the J-aggregates when the plasmon band was optically excited with a femtosecond pulse of light. Reversible charge storage of approximately 300 electrons by the 10-nm-diameter nanoparticles was shown. Scanning near-field optical microscopy studies on organized patterns of closely spaced metallic nanoparticles reveal collective plasmon character. Ultimately, the unusual photochemical properties of functionalized nanoparticles is expected to enable a modulation of collective plasmon properties for subdiffraction limited photon propagation in nanostructures.
J. Hranisavljevic, N.M. Dimitrijevic, G. A. Wurtz, J.S. Im, and G.P. Wiederrecht, J. Am. Chem. Soc., 124, pp. 4536-7 (2003)