Molecular Order in Langmuir−Blodgett Monolayers of Metal−Ligand Surfactants Probed by Sum Frequency Generation

Abstract

Molecular organization of Langmuir-Blodgett (LB) monolayers of novel copper-containing metal-ligand surfactants was characterized by the surface-selective vibrational sum frequency generation (SFG) spectroscopy. The orientational and conformational order inferred from the SFG peak amplitudes and line shapes were correlated with the two-dimensional phases of the monolayers observed in the compression isotherms. The octadecyl-pyridin-2-ylmethyl-amine (L(PyC18)) ligand by itself shows good amphiphilic properties, as indicated by the high monolayer collapse pressure at the air/water interface, but its LB films transferred onto fused silica exhibit a high degree of trans-gauche conformational disorder in the alkyl tails. Coordination of copper(II) ions to the chelating head group enhances the molecular alignment and reduces the fraction of gauche defects of the alkyl chains. Monolayers of single-tail (L(PyC18)Cu(II)Cl(2)) and double-tail [(L(PyC18))(2)Cu(II)]Cl(2) metallosurfactants show distinctly different behavior of their molecular organization as a function of the area per molecule. Our observations suggest metal-ligand interactions as a pathway to induce molecular order in LB monolayer films.

Molecular Recognition at Mineral Interfaces: Implications for the Beneficiation of Rare Earth Ores

“…vSFG is a second-order surface specific spectroscopy [55][56][57] that is uniquely capable of probing interfacial molecular species to quantify interfacial populations 58,59 and molecular ordering. 52,[60][61][62] Due to the evenorder field interactions, only species at an interface where local symmetry is broken can generate appreciable vSFG signals, thus making it an interface specific spectroscopy and an ideal tool to probe surface chemistry and complex interfaces. The measured vSFG intensity is proportional to the square of second order nonlinear susceptibility, (2) , of the sample and incident driving laser fields, (EIR and ENIR).…”

A new approach to vibrational sum frequency generation spectroscopy using near infrared pulse shaping

“…This sensitivity to local symmetry makes vSFG a powerful surface specific spectroscopy by providing insight into only the ordered molecular layers at an interface. 11,15,[28][29][30][31][32][16][17][18][19][24][25][26][27] In the limit that χ (2) NR is negligible, the vSFG spectrum is dominated by the molecular resonances at the interface and their interferences with one another. On the other hand, when χ…”

Temporal effects on spectroscopic line shapes, resolution, and sensitivity of the broad-band sum frequency generation

“…This is exemplified by the diversity of recent applications of the SFG spectroscopy, which include studies of structure and dynamics of aqueous interfaces, 1-5 biological membranes, 6 proteins and bioadhesion, 7,8 lung surfactant, 9,10 catalysis, 11 polymers, [12][13][14][15] monolayer materials, [16][17][18] environmental interfaces, 19,20 and imaging of corrosion processes. This is exemplified by the diversity of recent applications of the SFG spectroscopy, which include studies of structure and dynamics of aqueous interfaces, 1-5 biological membranes, 6 proteins and bioadhesion, 7,8 lung surfactant, 9,10 catalysis, 11 polymers, [12][13][14][15] monolayer materials, [16][17][18] environmental interfaces, 19,20 and imaging of corrosion processes.…”