Interaction between Frenkel exciton and surface plasmon

我们发现了贵金属纳米粒子直接被J聚集体(J聚集体/贵金属纳米粒子)覆盖的独特的光谱性质。在吸收光谱中，在表面等离子激元带处观察到J带位置的光谱凹陷。只有菁染料的J带位于金属颗粒的表面等离激元带，才能观察到这一反常光谱特征。其他染料以单体、二聚体、H-聚集体和J-聚集体的形式吸附在金属颗粒上，其J-带位于金属的带间跃迁带内，没有出现明显的凹陷现象。另一方面，当温度从290K降至90K时，倾角面积增大，倾角位置蓝移，倾角宽度变窄。在J-聚集体/氨硫醇/贵金属纳米粒子的情况下，我们发现了J-聚集体吸收放大、表面等离子激元介导的强共振荧光以及激发J-聚集体的有效波长范围显著扩大等特殊的新特征。这些特殊的特征表明表面等离子体激子和Frenkel激子之间的相互作用增强。重要的是激发态J-聚集体的产生效率更高，波长范围更宽，因为我们可以预期激发态J-聚集体的整体捕光效率将大大提高。本工作中观察到的两种光谱特征--抑制相互作用和增强相互作用，都可以用一个简单的偶极-偶极相互作用模型来再现。结果表明，贵金属纳米粒子表面形貌的不同导致了不同的相互作用模式。

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.