RESUMO
We investigate the fluorescence from submonolayer porphyrin molecules near silver-polymer core-shell nanoparticles (NPs) at a well-controlled separation distance of about 1 nm - 5 nm. When porphyrin molecules are deposited on silver NPs with the plasmonic resonance peak at about 410 nm, which matches very closely with the 405-nm excitation laser and the absorption band of porphyrin molecules, their emission intensity is found to be enhanced due to the plasmonic resonant excitation enhancement, and shows a decline as the increasing polymer shell thickness. Meanwhile, the lifetime results demonstrate that there exists the fluorescence quenching due to the charge transfer and nonradiative energy transfer losses, which is also the main reason that the maximum enhancement factor obtained in experiment is only about 2.3, although the theoretical one is above 60 according to the electric field distribution near silver NPs calculated by finite-difference time-domain method.
RESUMO
ZnTPP (Zinc-Tetraphenylporphyrin) is one of the most common nanostructured materials, having high stability and excellent optoelectronic properties. In this paper, the fluorescence features of self-assembled ZnTPP monomers and aggregates on Au(111) surface are investigated in detail on the nanometer scale with scanning tunneling microscopy (STM). The formation of ZnTPP dimers is found in thick layers of a layer-by-layer molecular assembly on Au substrate with its specific molecular arrangement well characterized. Tip-induced luminescence shows a red shift from tilted dimers comparing with the behavior from monomers, which can be attributed to the change of vibrational states due to the intermolecular interaction and the increasing dielectric effect. The nanoscale configuration dependence of electroluminescence is demonstrated to provide a powerful tool aiding the design of functional molecular photoelectric devices.