Synthesis and characterization of a thiol-tethered tripyridyl porphyrin on Au(111)
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abstract
Porphyrins are actively studied for use in molecular and organic electronic components of devices because of their diverse tunable optical and electronic properties. In this study, mixed self-assembled monolayers (SAMs) of dodecanethiol and a tripyridyl porphyrin attached to a thiol tether via a perfluorinated phenyl ring (TPy3PF4-SC5SH) were prepared on Au(111) substrates. The synthetic strategy allows for rapid formation of derivatives with different tethers. The surface structural and electronic properties of mixed monolayer SAMs of the porphyrin inserted into the dodecanethiol matrix were investigated using scanning tunneling microscopy (STM), atomic force microscopy (AFM), Fourier transform infrared reflection-absorption spectroscopy (FT-IRAS), and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) calculations were also employed to evaluate the analytical vibrational frequencies of the TPy 3PF4-SC5SH molecule as well as its electronic structure. For the mixed monolayers, the morphology of the porphyrin molecules was probed by STM where it was found that the molecules assembled into domains of 2 and 6 nm. AFM shows that the molecules protrude above the n-dodecanethiol layer by 0.9 nm, while by STM, apparent heights of only 0.5 nm were observed, suggesting limited tunneling efficiency. Stochastic switching of the porphyrin molecules was also observed during STM measurements in the mixed monolayer and is likely associated with conformational changes within the monolayer since these molecules tended to insert near defects within the SAM. 2008 American Chemical Society.
