Reversible work function changes induced by photoisomerization of asymmetric azobenzene dithiol self-assembled monolayers on gold

We measured reversible changes in the work function (Delta phi(Au)) 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. Delta phi(Au) 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 Delta phi(Au) against photoisomerization. Hence, a direct correlation between Delta phi(Au) and changes in molecular dipole moments was obtained. (C) 2008 American Institute of Physics.