Synthesis and characterization of aromatic self-assembled monolayers containing methylene and ethyleneglycol entities by means of sum-frequency generation spectroscopy

• Published in: Thin solid films Vol. 500; no. 1; pp. 268 - 277
• Main Authors: Dreesen, L., Sartenaer, Y., Peremans, A., Thiry, P.A., Humbert, C., Grugier, J., Marchand-Brynaert, J.
• Format: Journal Article Web Resource
• Language: English
• Published: Lausanne Elsevier B.V 03-04-2006; Elsevier Science; Elsevier
• Subjects: Adsorption; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Biomaterials; Chemical Physics; Condensed Matter; Fundamental and applied biological sciences. Psychology; Materials Science; Miscellaneous; Molecular biophysics; Optical spectroscopy; Optics; Photochemistry. Photosynthesis. Bioluminescence; Physical, chemical, mathematical & earth Sciences; Physics; Physique; Physique, chimie, mathématiques & sciences de la terre; Proteins; Radiation-biomolecule interaction; Self-assembled monolayers; Spectra, photodissociation, and photoionization; luminescence; Sum-frequency generation; Optical spectroscopy; Sum-frequency generation; Adsorption; Self-assembled monolayers; Biomaterials; Self assembly; Monolayer; Ethylene glycol; Stacking sequence; Sum frequency; Experimental study; Protein; Tilt angle; Macromolecule; Aromatic compound; Nuclear magnetic resonance; Vibrational mode; Chemical synthesis; Defect formation; Organic compounds
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2005.11.013

We use infrared-visible sum-frequency generation (SFG) spectroscopy in order to investigate the adsorption properties on Pt(111) of molecules having CH
3–C
6H
4–(O–CH
2–CH
2)
n
–O–(CH
2)
m
–SH as general chemical formula. We synthesized three molecules defined by the values
m
=
5
n
=
4,
m
=
11
n
=
4,
m
=
11
n
=
8 and characterized them by Nuclear Magnetic Resonance spectroscopy. Thanks to spectroscopic measurements, we show that these molecules build self-assembled monolayers on Pt(111). First, the weak SFG signals arising from the ad-layer indicate low order and surface coverage of the substrate by these molecules. Next, the vibrational fingerprints of the aforementioned molecules are determined between 2825 and 3125 cm
−
1 and the observed SFG spectral features are ascribed on the basis of the analysis of shorter and simpler molecules (1-dodecanethiol, 4-methylbenzenethiol and CH
3–C
6H
4–O–(CH
2)
11–SH) also adsorbed on Pt(111). The occurrence of methylene vibration modes indicates a significant amount of chain defects whatever the n and m numbers are. Finally, the identification of a particular vibration mode, characteristic of the aromatic ring, enables us to qualitatively discuss the effect of the number of methylene and ethylene glycol entities on its orientation. More precisely, higher these numbers, more tilted (with respect to the substrate normal) the aromatic ring plane is.