In Situ Surface-Enhanced IR Absorption Spectroscopy on CO Adducts of Iron Protoporphyrin IX Self-Assembled on a Au Electrode

Abstract

The surface coordination chemistry of carbon monoxide with the reduced form (Fe(II)PP) of iron(III) protoporphyrin IX (Fe(III)PP) monolayer self-assembled on a Au electrode in 0.1 M HClO4 was studied for the first time by using in situ ATR-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). Both mono- and biscarbonyl adducts [simplified as Fe(II)(CO)PP and Fe(II)(CO)2PP, respectively] were detected, depending on the history of potential control. Initially, the Fe(II)(CO)PP predominates, and the intermediate transition potential for the conversion of Fe(II)(CO)PP to Fe(III)PP and CO was spectrally determined to be ca. 0.09 V (vs SCE). The ratio of Fe(II)(CO)2PP and Fe(II)(CO)PP increases after a potential excursion to a sufficiently positive value. Fe(II)(CO)2PP is much more stable against its electro-oxidation to Fe(III)PP than its counterpart Fe(II)(CO)PP with increasing potential. The observed change of coordination properties may be ascribed to an irreversible structural reorganization of the FePP adlayer caused by the potential excursion.

Structure and growth mechanism of self-assembled monolayers of metal protoporphyrins and octacarboxylphthalocyanine on silicon dioxide

“…Other studies show that the optical and electrical properties of conjugated macrocycle thin lms are extremely sensitive to adsorption of gas molecules (NO 2 , SO 2 , and CO 2 ), making them promising candidates for gas sensor applications [16][17][18][19][20][21] Among various strategies for the formation of macrocycle lms required for the design of these molecular devices, the leading advantage of self-assembly method is the covalent bonding between the molecules and the surface, which replaces weak van der Waals or hydrogen bonding as in the case of Langmuir-Blodgett lms. Therefore self-assembled thin lms offer very good chemical and physical stability.…”

Adsorption of 2‐amino‐5‐cyanopyridine on a gold surface as probed by surface‐enhanced Raman spectroscopy

“…The dramatic change in the Stark effect slope of CN − at ca −0.6 V indicated a subtle orientation change. In addition, studies on CO via in situ ATR-surface-enhanced infrared absorption spectroscopy were performed by Cai [12] and surface-enhanced IR spectroscopy by Osawa. [13] They deduced the molecular orientation on the basis of the electrochemical Stark effect and surface selection rules.…”

Phenylenediamine-Based FeNx/C Catalyst with High Activity for Oxygen Reduction in Acid Medium and Its Active-Site Probing

“…These results indicate that both CO and NO x can not bind to the active site of FeN x /C catalyst (Figure d). It has been reported that CO can bind to Fe II porphyrins but can not to Fe III porphyrins . The insensitivity of P m PDA-FeN x /C to CO and NO x suggests that Fe valence state may be Fe III if active site contains iron atom.…”

“…It has been reported that CO can bind to Fe II porphyrins but can not to Fe III porphyrins. 19 The insensitivity of PmPDA-FeN x /C to CO and NO x suggests that Fe valence state may be Fe III if active site contains iron atom.…”