The relationship between the physical properties of azobenzene self-assembled monolayers (SAMs) on gold surfaces (CnH2n+1-O-φ-N=N-φ-C(O)NHCmH2mS-Au, abbreviated as CnAzoCmS-Au) and the structural bature of the parent alkanethiol molecules was investigated by electrochemical in-siut Fourier transform infrared reflection/absorption spectroscopy (FTIR-RAS). The 2H+, 2e- redox behavior from azobenzene to hydrazobenzene in CnAzoCmS-Au monolayers was confirmed, as reported in our recent paper (Langmuir 1998, 14, 619-624). The in-situ spectra showed unambiguously that the molecular orientation and electrochemical stability of azobenzene SAMs are highly related to the structural nature of the azobenzene alkanethiols. In particular, the longer the alkyl chains in the azobenzene alkanethiols, the more stable and closely packed are the monolayers. A potential-induced orientational switching of the terminal ethoxy group was observed for C2AzoC4S-Au, which is different from the intermolecular hydrogen-bonding 'fixed' alkyl chain below the azobenzene moiety.
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