Structural and Electron-Transfer Characteristics of O-, S-, and Se-Tethered Porphyrin Monolayers on Si(100)

Abstract

Monolayers of two classes of Zn porphyrins have been prepared and examined on Si(100). These molecules, designated as ZnPBzX- and ZnPCH2X-, contain either a benzyl (-Bz-) or a methylene (-CH2-) unit terminated with a Group VI atom (X = O, S, Se) appended to a meso-position of the porphyrin, with the nonlinking meso-substituents consisting of either mesityl (-Bz- class) or p-tolyl and phenyl (-CH2- class) units. The two series of ZnPBzX- and ZnPCH2X- monolayers on Si(100) were examined using a variety of techniques, including X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and various electrochemical methods. The studies reveal the following characteristics of the ZnPBzX- and ZnPCH2X- monolayers. (1) Surface binding can be readily achieved to Si(100) with both relatively short (-Bz-) and very short (-CH2-) tethers regardless of the nature of the Group VI anchoring atom (O, S, Se). (2) The longer -Bz- tether affords monolayers with the porphyrin ring in a somewhat more upright orientation with respect to the surface than the shorter -CH2- tether. The more upright adsorption geometry of the porphyrins bearing the former type of linker leads to a higher packing density and more homogeneous redox thermodynamics. (3) The kinetics of electron transfer does not depend on the type of Group VI atom used for anchoring to the Si(100) surface. On the other hand, the type of linker does affect the electron-transfer rates, with the monolayers bearing the -CH2- linker exhibiting systematically faster rates than those bearing the -Bz- linker. Collectively, the studies reported herein provide a detailed picture of how the anchor atom and the linker type influence the structural and electron-transfer characteristics of these general classes of monolayers.

A Carbon NanohornPorphyrin Supramolecular Assembly for Photoinduced Electron‐Transfer Processes

“…The precursor porphyrin with a methyl ester group (1) was prepared in 16 % yield by the Lindsey method [18] and the intermediate porphyrin with an alcohol group (2) was obtained in 98 % yield by using a literature procedure. [19] Porphyrin with crown ether (3) was obtained in moderate yield (35 %) by esterification of alcohol 2 [18] with 4'-(chlorocarbonyl)benzo [18]crown-6 in refluxing dichloromethane. Finally, the free-base porphyrin 3 was treated with zinc acetate to obtain the desired Crown À ZnP in 49 % yield.…”

“…Then, the solvent was evaporated and the resultant colorless solid was redissolved in dry CH 2 Cl 2 (20 mL). Then, pyridine (1 mL) was added followed by porphyrin 2 [19] (see Scheme 2, 50 mg, 0.05 mmol). The reaction mixture was refluxed under an argon atmosphere for four days.…”

“…The solvent was evaporated, and the crude product was purified by column chromatography (silica gel, CH 2 Cl 2 followed by CH 2 Cl 2 /CH 3 OH 90:10). Evaporation of the solvents yielded the desired free-base porphyrin crown-H 2 P compound 3 as a purple solid (19 Synthesis of CrownÀZnP: Crown-H 2 P 3 (16 mg, 0.014 mmol) was dissolved in CHCl 3 (10 mL), saturated zinc acetate in methanol was added, and the resulting mixture was refluxed for 2 h. Then, the reaction mixture was washed with water and dried over anhydrous Na 2 SO 4. The crude …”

Mixed assembly of ferrocene/porphyrin onto carbon nanotube arrays towards multibit information storage

“…Figure 3(c) shows the FTIR spectrum of solid phase ruthenium porphyrin RuTPP(CO)(EtOH). Several strong absorption peaks can be observed at 1957 and 1008 cm -1 , which are attributed to carbonyl stretching [14,15] and porphyrin pyrrole ring breathing mode [16,17]. After 4-aminopyridine mounted SWCNTs-Si surfaces were immersed in a chloroform solution of 0.5 mg mL -1 ruthenium porphyrin for 24 hours, the FTIR spectrum shown in Figure 3 when surface mounted.…”

Expanding the Repertoire of Molecular Linkages to Silicon: Si–S, Si–Se, and Si–Te Bonds

“…23 Bonding of SAMs through Si−O, Si−S, Si−Se, Si−Te, and Si− N bonds as well as SiX (X = halide) coverage were examined; for heavier atoms (Te versus Se versus S versus O), additional electronic states are available, which can affect electron transfer to and from molecules attached to a silicon surface. 21,24 In contrast to the vast literature of SAMs bonded to silicon through Si−C 25,26 and Si−O linkages, 27,28 the development of silicon−chalcogenide bond-forming reaction schemes on silicon surfaces has only just begun, in spite of the strong impetus to study, understand, and apply them. The field of Si− S-and Si−Se-based SAMs on surfaces via solution (nonvacuum) chemistry can be summarized in one paragraph.…”