Synthesis and Characterization of a Thiol-Tethered Tripyridyl Porphyrin on Au(111)

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 (TPy 3 PF 4 -SC 5 SH) 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 3 PF 4 -SC 5 SH 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.

Role of S–Au labile bonding in stochastic switching of molecular conductance studied by STM

“…In these STM studies, molecules of interest have been inserted in an alkylthiol self-assembled monolayer (SAM). The observed stochastic conductance switching has been explained by conformational changes [7] like in more recent works using STM [2,8] or break junctions [1], or molecular hybridization changes at the interface with gold [9,10]. However, independent STM studies on SAMs on gold have reported similar stochastic switching effects for thiol molecules, which cannot exhibit any conformational changes [11].…”

Highly Efficient Visible‐Light‐Induced Photocleavage of DNA by a Ruthenium‐Substituted Fluorinated Porphyrin

“…With the appropriate choice of mobile phase the target porphyrin was obtained in low but not unreasonable yields for this procedure. [12] Coordination of Ru(bipy) 2 Cl 2 to the pyridyl nitrogen atoms was accomplished by previously described procedures. [13] It has been noted that coordination of three Ru(bipy) 2 Cl 2 moieties to the pyridyl nitrogen atoms of a porphyrin is extremely difficult under refluxing conditions in acetic acid.…”

Single molecular switch based on thiol tethered iron(II)clathrochelate on gold

“…Three electrodes electrochemical cell with gold disk electrodes 1.6 mm diameter (Bioanalytical system, USA), Ag/AgCl (3 M NaCl saturated with AgCl) reference electrode and platinum counter electrode were used. CV and EIS experiments were carried out in argon saturated 0.1 M Na 2 SO 4 containing K 3 [Fe(CN) 6 ]/K 4 [Fe(CN) 6 ] (0.5 mM each) as the supporting electrolyte to examine the monolayer properties at 25 • C [28,29]. CV measurements were performed from −0.2 to 0.2 V at different scan rate in 0.1 M Na 2 SO 4 to find the differential capacitance Electrochemical impedance spectroscopy performed in 0.1 M Na 2 SO 4 by applying an AC impedance in a frequency range between 1 Hz and 100 kHz with a perturbation signal of 5 mV at 0 V [29,30].…”

“…The electronic properties of single molecules or small groups of molecules have been studied by constructing different electrical test beds including electrical and mechanical break junctions [5,8], crosswire junctions [2], conducting-probe atomic force microscopy [28] and scanning tunneling microscopy (STM) [2][3][4][5][6][7][8]28]. STM is a powerful surface analysis technique, as it enables the observation of individual molecules with atomic resolution on surfaces.…”

“…In addition to topographic details, STM images can elucidate details of the local tunneling probability as well as the electronic density of molecular orbitals (e.g., highest occupied molecular orbital, HOMO, and lowest unoccupied molecular orbital, LUMO) participating in the tunneling process and thus can influence the local transport behaviour. Recently, Chan and co-workers [28] have reported thiol-functionalized porphyrins mixed dodecanethiol (DDT) selfassembled monolayers for molecular-based electronics.…”