Covalent Bonding of Alkene and Alkyne Reagents to Graphitic Carbon Surfaces

Abstract

Various aromatic and aliphatic alkynes and one alkene were covalently bonded to sp(2)-hybridized carbon surfaces by heat treatment in an argon atmosphere. X-ray photoelectron spectroscopy, Raman, and FTIR spectra of the modified surfaces showed that the molecules were intact after the 400 degrees C heat treatment but that the alkyne group had reacted with the surface to form a covalent bond. Alkynes with ferrocene and porphyrin centers exhibited chemically reversible voltammetric waves that could be cycled many times. Atomic force microscopy of the modified surfaces indicated a thickness of the molecular layer consistent with monolayer coverage, and surface coverage determined by voltammetry was also in the monolayer range. Raman spectroscopy of the porphyrin monolayers formed from a porphyrin alkyne showed no evidence for dimer formation, although multilayer formation may occur at undetected levels. FTIR spectra of the porphyrin-modified carbon surfaces were well-defined, similar to the parent molecule, and indicative of an average tilt angle between the porphyrin plane and the surface normal of 37 degrees . The bond between the molecular monolayer and the carbon surface was quite stable, withstanding sonication in tetrahydrofuran, mild aqueous acid and base, and repeated voltammetric cycling in propylene carbonate electrolyte. Heat treatment of alkynes and alkenes appears to be a generally useful method for modifying carbon surfaces, which can be applied to both aromatic and aliphatic molecules.

Covalent modification of graphitic carbon substrates by non-electrochemical methods

“…McCreery's study [65] described above provides convincing evidence for the formation of covalently attached monolayers through thermal reaction with alkynes and alkenes with PPF, and the results of Godet and co-workers obtained at amorphous carbon support that conclusion [66,67]. The mechanism of the reaction is not clear however.…”

“…In general, the procedures are similar to those employed for covalent modification of silicon and diamond surfaces. McCreery was the first to report modification of graphitic carbon, in the form of PPF, by thermal reaction with alkynes and an alkene [65]. The method was demonstrated using alkynes with the following substituents: Zn(II) porphryin, ferrocenyl, trifluorotolyl and 5-chloropentyl, and with a Zn(II) porphyrin alkene derivative.…”

Chemically Modified Carbon Nanotubes: Derivatization and Their Applications

“…Comparing the oxidation of primary, secondary and tertiary amines, the tertiary amines undergo oxidation easily compared to primary and secondary amines which were confirmed by the strong, sharp, irreversible oxidation peaks appear at least positive potentials. This kind of observed behavior might be due to the stabilization of amine cation radical by the presence of alkyl substituents [22,23]. The lifetimes of the radical cation formed increases from primary, secondary to tertiary amines.…”

Modification of Carbon Electrode Surfaces

“…Oxidation peaks shift more negative, with increased sharpness, as alkyl substituents are added to the amine group. Therefore, the generation of radical cations is most facile for tertiary amines and least facile for primary amines, and is related to the stabilization of cation radical by the alkyl substituents [92,93]. Intramolecular electron transfer from a redox group conjugated with the amino group also favors the electrografting [94].…”