We measured reversible changes in the work function (Δ φAu) of gold substrates modified by asymmetric azobenzene dithiol self-assembled monolayers (SAMs) following photoisomerization and thermal recovery of the azo unit. The azobenzene derivative SAMs were photoisomerized to cis form by UV irradiation. Δ φAu was monitored in real time during thermal recovery to trans form by ultraviolet photoelectron spectroscopy using a synchrotron light source. Changing the substituted functional group in the p′ position of the azobenzene from electron donating to electron withdrawing resulted in opposite responses of Δ φAu against photoisomerization. Hence, a direct correlation between Δ φAu and changes in molecular dipole moments was obtained.
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