Ultrafast electronic decay through molecular chains

• Applicant: Professor Dr. Alexander Kuleff
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 543102824

The removal of a core electron from a molecule populates highly excited ionic states that usually relax by an ultrafast electronic decay emitting a secondary electron from the system. The decay of deep-core vacancies typically takes place within the atom bearing the initial vacancy and is only weakly affected by the chemical environment. The situation changes when inner-valence vacancies decay. In this case, very often non-local transitions, involving electrons not "belonging" to the initially ionized constituent of the system, start to be operative. In recent studies, we showed that such non-local decays can take place in molecules where the two system sub-units participating in the decay are connected with a long carbon chain: a vacancy localized on one sub-unit relaxes by emitting an electron from the sub-unit connected to the opposite end of the chain. The decay was found to be extremely efficient (in the few-femtosecond time scale) and to depend only linearly on the length of the carbon chain. As the process can be viewed as an ultrafast energy transfer through the carbon chain, it allows to study the efficiency of energy transfer through a medium. The present project aims at performing a systematic study, using ab initio methods only, of the non-local electronic decay through molecular chains, investigating the dependence of the process on the degree of saturation and the pi-conjugation of the chain, the role of the "energy-donor" and "energy-acceptor" species, as well as the possibility to increase the efficiency of the decay by tuning the relaxation transition to an exciton resonance of the chain. We expect that we will be able to identify a small set of chemical descriptors and physical characteristics of the system constituents that will allow an easy design of donor-bridge-acceptor systems in which an efficient non-local decay can take place, emitting electrons from the desired remote end of the system.

• DFG Programme: Research Grants