Stuty of the Tunneling Mechanism for Long Range Electron Transfer in Azobenzene Self-assembled Monolayers

The tunneling mechanism for long range electron transfer in azobenzene self-assembled mololayers on gold has been studied by electrochemical techniques. We have prepared for the first time a series of azobenzene-tethered alkanethiol monolayers on gold electrode surface with varied number of methylenes in the alkyl chain spacer (CH₃CH₂-φ-N=N-φ-C(O)NH-(CH₂) _nSH/Au, n= 2, 3, 4, 6). The apparent electron transfer rate constants k_app of azobenzene to the underlying electrode are found to fall off exponentially with increasing the length of alkyl chain spacers. The electron tunneling constant β for the electron transfer in the present system are estimated to be 1.35±0.20 per CH₂ from the logarithmic k_app versus n (number of methylenes in the alkyl chain spacer) plot.