RA-IR studies on the structure of mercapto-ended azobenzene derivatives inself-assembled monolayers

Self-Assembled Monolayers (SAMs) were prepared from mercapto-ended azobenze ne derivatives with the structure of In-C(n)H(2n+1)AzoO(CH2)(m)SH (n=4,6,8, 10,12; m=3,5). The structure of these SAMs was thoroughly studied with graz ing-angle incident reflection absorption FTIR technique and wettability mea surement. The results suggested that the plane of Azobenzene system of the assembling molecules in the SAMs lies bn its back with an approximate angle of 22(0) included between the substrate surface normal and the Azobenzene plane. Tail alkyl groups (n-CnH2n+1) in these assembling molecules were con sidered to be in an all-trans conformation, as if they were in a crystallin e-like environment. And the C-C-C plane of these all-trans tail alkyl group s, while n greater than or equal to8, ties also on its back with an angle a bout 70(0) between its plane and the substrate surface normal. The conforma tion of these head groups (-O(CH2)(m)SH) in SAMs are disturbed by many stru ctural factors. While m=3 or 5, the head group chain was proposed to remain in a gauche conformation to fit the upright orientation of the Azobenzene plane. The packing density was investigated by measuring the contact angle of water on these SAMs. The results showed that the self-assembled monolaye r films are perfectly packed and the coverage density might be improved wit h increasing the length of both tail and head alkyl chains.