Abstract
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.
Highlights
Is crucial to synthesis basic units of functional structures
We investigate the self-assembled growth of multilayer ZnTPP molecules formed on Au(111) surface which is widely used for porphyrin monolayers[2,25] and study their optical properties layer by layer
It has been proved that the top-layer porphyrin molecules would emit photons governed by resonant nanocavity plasmons (NCPs) in a highly confined scanning tunneling microscopy (STM) nanocavity[25] with the bottom molecules acting as decoupling spacer
Summary
Utilizing the variation from molecular monomer to aggregates, the fluorescence emission energy could be predictably changed to broaden the wavelength regime. It is of importance to tune the local assembled and spectroscopic properties for understanding the aggregation phenomena and the energy transfer in tunnel junction, and meeting some specific optoelectronic requirements. The configuration change process from monomers to aggregates and its influence on the luminescence is not very clear, but obviously important for designing multi-band photoelectric devices and exploring the mechanism of molecular energy level transition. All of the featured structures can give relevant, well-characterized spectra in the nanoscale tunneling junction. Red-shift and the enhancement of fluorescence, which were obtained on the tilted dimers array at the nanoscale, are attributed to the intermolecular interaction of the dominant molecular dimers and the increasing effective dielectric constant of the tunnel junction
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