Photoemission from Azobenzene Alkanethiol Self-Assembled Monolayers

Photoelectron spectra were measured for films of self-assembled azobenzene-terminated alkanethiol monolayers on gold using synchrotron radiation. The azobenzene was substituted either by CF 3 or CH 3 in the para position. As a result of the orientational order of the molecules within the films, as indicated by the pronounced angle dependence of the photoemission spectra, it is possible to identify laser-induced optical switching of the molecules using combined laser and synchrotron pulses. Molecular switching, i.e., photoisomerization, is recognized by relative intensity changes of the photoemission peaks and also by spectral shifts to higher binding energies. The latter result from a change of the molecular dipole moment associated with the trans-cis laser-induced photoisomerization of the azobenzene-CF 3 group.