Dynamics of charge transfer in self-assembled monomolecular films

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The main objective of the project is a systematic study of femtosecond charge transfer (CT) dynamics in potential building blocks and components of molecular electronics (ME) to get quantitative data on the most relevant parameters - as valuable input for theory and molecular design - and to achieve a better understanding of the underlying processes. To this end, we will apply synchrotron-based resonance Auger electron spectroscopy (RAES) in combination with the core hole clock (CHC) method to the monomolecular assembles of the target molecules on conductive substrates. The above approach relies on decomposition of the suitable RAES spectra into the parts related to the standard decay of the excited state and CT of the resonantly excited electron to the substrate. It is contact-free and uses the known lifetime of inner shell vacancy, appearing in the course of the Auger process, as an internal time reference. Due to the special design of the target molecules, the CT pathway will be unambiguously defined by the resonant excitation of the tail group (nitrile, etc.) attached to the molecular backbone which, in its turn, will be attached to the substrate by a suitable head group. As compared to the first part of the project (ZH 63/14-1), we intend (i) to test the applicability range of the RAES-CHC approach by selection of special and limiting cases such as reverse CT, etc, (ii) to get broader information on potential molecular wires, (iii) to clarify the contribution of the anchor group to CT dynamics and, if possible, to give recommendation for its optimal choice, (iv) to test the potential molecular electronics devices such as substitution-free rectifiers (azulene-based compounds) and light-driven switches (azobenzene-based compounds), and (v) to extend the RAES-CHC approach to new systems. A special attention will be put on the study of molecular-orbital-selective CT dynamics which can be addressed within the RAES-CHC approach by either energy or symmetry selection, as shown by us during the first part of the project (ZH 63/14-1). The CT dynamics experiments will be accompanied by the measurements of static CT (using the mercury drop method) to obtain a consistent and comprehensive picture of CT phenomena in the target systems and other building blocks of ME.