Characterization of Self-Assembled Monolayers of Porphyrins Bearing Multiple Thiol-Derivatized Rigid-Rod Tethers

Abstract

A series of multithiol-functionalized zinc porphyrins has been prepared and characterized as self-assembled monolayers (SAMs) on Au. The molecules, designated ZnPS(n) (n = 1-4), contain from one to four [(S-acetylthio)methyl]phenylethynylphenyl groups appended to the meso-position of the porphyrin; the other meso-substituents are phenyl groups. For the dithiol-functionalized molecules, both the cis- and the trans-appended structures were examined. The ZnPS(n) SAMs were investigated using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and various electrochemical methods. The studies reveal the following characteristics of the ZnPS(n) SAMs. (1) The ZnPS(n) molecules bind to the Au surface via a single thiol regardless of the number of thiol appendages that are available per molecular unit. (2) The porphyrins in the ZnPS(3) and ZnPS(4) SAMs bind to the surface in a more upright orientation than the porphyrins in the ZnPS(1), cis-ZnPS(2), and trans-ZnPS(2) SAMs. The porphyrins in the ZnPS(3) and ZnPS(4) SAMs are also more densely packed than those in the cis-ZnPS(2) and trans-ZnPS(2) SAMs. The packing density of the ZnPS(3) and ZnPS(4) SAMs is similar to that of the ZnPS(1) SAMs, despite the larger size of the molecules in the former SAMs. (3) The thermodynamics and kinetics of electron transfer are generally similar for all of the ZnPS(n) SAMs. The general similarities in the electron-transfer characteristics for all of the SAMs are attributed to the similar binding motif.

Study of the adsorption kinetics of thiol-derivatized porphyrin on the surface of gold electrode

“…Supposed the porphyrin molecules were well packed on the surface of electrode and the distance of chain-to-chain was 4.4 Å and from the S-S distance, we could calculate the tilt-angles of porphyrin SAMs on Au. As could be seen in Table 2, the calculated tilt-angles were qualitatively in agreement with the literature values [33,34]. Therefore, the possible structure of porphyrin on Au was showed in Scheme 1.…”

Electronic and structural studies of immobilized thiol-derivatized cobalt porphyrins on gold surfaces

“…Molecules with several thiol linkers tend to adsorb under the formation of multiple thiolates while some of the linkers remain not bonded [6,[28][29][30]. Rigid linkers lead to the attachment of single thiols to the surface [31] and the flexibility of the linkers is therefore important in order to achieve multiple thiol attachment. In case of the protected porphyrin layers the highest amount of not bonded linkers (S2) is observed.…”

Molecular orientation of thiol-derivatized tetraphenylporphyrin on gold studied by XPS and NEXAFS

“…Several researchers have prepared porphyrin layers by immobilizing the molecules on the surface via linkers that contain thiol groups [6][7][8][9][10][11]. Thiols are commonly used as anchor groups to attach organic molecules on gold surfaces.…”