Molecular orientation and electrochemical stability of azobenzene self-assembled monolayers on gold: An in-situ FTIR study

The relationship between the physical properties of azobenzene self-assembl ed monolayers (SAMs) on gold surfaces (CnH2n+1-O-phi-N=N-phi-C(O)NHCmH2mS-A u, abbreviated as CnAzoCmS-An) and the structural nature of the parent alka nethiol molecules was investigated by electrochemical in-situ Fourier trans form infrared reflection/absorption spectroscopy (FTIR-RAS). The 2H(+), 2e( -) redox behavior from azobenzene to hydrazobenzene in CnAzoCmS-Au monolaye rs was confirmed, as reported in our recent paper (Langmuir 1998, 14, 619-6 24). The in-situ spectra showed unambiguously that the molecular orientatio n and electrochemical stability of azobenzene SAMs are highly related to th e structural nature of the azobenzene alkanethiols. In particular, the long er the alkyl chains in the azobenzene alkanethiols, the more stable and clo sely packed are the monolayers. A potential-induced orientational switching of the terminal ethoxy group was observed for C2AzoC4S-Au, which is differ ent from the intermolecular hydrogen-bonding "fixed" alkyl chain below the azobenzene moiety.