Interaction between Frenkel exciton and surface plasmon

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We have found a unique spectroscopic property of noble metal nano-particles directly covered with a J-aggregate monolayer (J-aggregate/noble metal nano particle). In the absorption spectra, the spectral dip at the position of the J-band was observed in the surface plasmon band. The anomalous spectral feature has been observed only in the case of the adsorption of cyanine dyes, whose J -band was in the surface plasmon band of metal particles. The dip did not appear for other dyes adsorbed on the metal particles as monomer, dimer, H-aggregate and J-aggregate whose J-band was in the interband transition band of the metal. On the other hand, cooling down the temperature from 290 K to 90 K has brought about increase of the dip area and blue shift of the dip position and the narrowing of the dip width. We have supposed that the appearance of the dip is related to the strong suppressive interaction between the surface plasmon and Frenkel exciton.In the case of J-aggregate/aminothiol/noble metal nano particle, we have found special new features as absorption enlargement in the region of the J -band, surface plasmon-mediated strong resonance fluorescence, and considerable expansion of effective wavelength region for excitation of the J-aggregate. These special features would suggest the enhanced interaction between the surface plasmon and Frenkel exciton. It is important that the excited-state J-aggregate can be generated much more efficiently and in much wider region of wavelength, because we could expect the largely increasing the overall light-harvesting efficiency.The observed both spectral features in this work, suppressive and enhanced interactions, could be reproduced by a simple dipole-dipole interaction model. It has been suggested that difference of the surface morphology of the noble metal nano particle induces the different interaction mode.