Determination of the Structure and Orientation of Organic Molecules Tethered to Flat Graphitic Carbon by ATR-FT-IR and Raman Spectroscopy

Abstract

Mono- and multilayers of nitroazobenzene (NAB), azobenzene (AB), nitrobiphenyl (NBP), biphenyl (BP), and fluorene (FL) were covalently bonded to flat pyrolyzed photoresist films (PPF) by electrochemical reduction of their diazonium derivatives. The structure and orientation of the molecular layers were probed with ATR-FT-IR and Raman spectroscopy. A hemispherical germanium ATR element used with p-polarized light at 65 degrees incidence angle yielded high signal/noise IR spectra for monolayer coverage of molecules on PPF. The IR spectra are dominated by in-plane vibrational modes in the 1000-2000-cm(-1) spectral range but also exhibit weaker out-of-plane deformations in the 650-1000-cm(-1) region. The average tilt angle with respect to the surface normal for the various molecules varied from 31.0 +/- 4.5 degrees for NAB to 44.2 +/- 5.4 degrees for FL with AB, NBP, and BP exhibiting intermediate adsorption geometries. Raman intensity ratios of NAB and AB for p- and s-polarized incident light support the conclusion that the chemisorbed molecules are in a predominantly upright orientation. The results unequivocally indicate that molecules electroreduced from their diazonium precursors are not chemisorbed flat on the PPF surface, but rather at an angle, similar to the behavior of Au/thiol self-assembled monolayers, Langmuir-Blodgett films, and porphyrin molecules chemisorbed thermally on silicon and PPF from alkyne and alkene precursors.

Charge transport in molecular electronic junctions: Compression of the molecular tunnel barrier in the strong coupling regime

“…Current density-voltage (J-V) curves shown are averages of four to eight junctions for a given molecule and thickness from a total of ∼300 fabricated and tested junctions. (19,30,31). The results in Fig.…”

Vibrational analysis of [4-[(E)-phenylazo] phenyl]ethanol based on the comparison between the experimental and DFT calculated Raman spectra

“…Different numerical and experimental factors can influence the Raman intensities. Indeed, Anariba et al [58] have shown that despite complex pre-resonance enhancements, the intensity of this band was also strongly correlated to the laser polarization for nitroazobenzene grafted on pyrolyzed photoresist film, while Painelli et al [59] have shown the effect of the solvent and the excitation lines on the relative intensities for [(S)-3-pivaloyloxy-1-(4′-nitro-4-azobenzene)pyrrolidine]. From a numerical point of view, the Raman intensities, as a function of the third derivatives of the energies, are both dependant on the energetic models (basis set truncation, treatment of electron correlation), the methods and the parameters used to calculate the analytical and numerical derivatives [60].…”

Factor Analysis for the Characterization of the Nano-Surface of the Nitroazobenzene-Modified Glassy Carbon Electrode

“…[13][14][15][16] The main aim of this manuscript is to apply a new powerful factor analysis method to the IR spectra of the nitroazobenzene modified GC electrode (NAB-GC) surface, bare GC surface and nitroazobenzene diazonium salt (NAB-DAS) for the structural qualitative characterization of the nanofilm, consisting of the surface of the modified NAB-GC electrode system, in order to test the existence of the nitroazobenzene molecules on the modified GC surfaces.…”