Charge-Transfer Dynamics in Azobenzene Alkanethiolate Self-Assembled Monolayers on Gold

We have studied the charge transfer dynamics in azobenzene-functionalized alkanethiolate self-assembled monolayers. We compare the core-hole clock technique, i.e., resonant vs. non-resonant contributions in the azobenzene autoionization of the C1s-π∗ core exciton, with the lifetime of a molecular resonance determined by two-photon photoemission spectroscopy using femtosecond laser pulses. Both techniques yield comparable charge-transfer times of 80±20 fs for a linker consisting of three CH2 groups and one oxygen unit. Thus the quenching of the excitation is about one order of magnitude faster than the time required for the trans to cis isomerization of the azobenzene photoswitch in solution.