Structure-Dependent Charge Transfer in Molecular Perylene-Based Donor/Acceptor Systems and Role of Side Chains

In organic electronics and optoelectronics several crucial physical processes are related to charge transfer (CT) effects. In this work, we investigate mixing behavior and intermolecular coupling of donor and acceptor molecules in thin films prepared by organic molecular beam deposition (OMBD). Diindenoperylene (DIP) and pentacene (PEN) are used as the donor materials, and perylene diimide derivatives PDIR-CN2 and PDIF-CN2 as the acceptor materials.. The formation of charge transfer complexes coupled in the electronic excited state vs. noninteracting phase separating components is studied by structural and optical techniques. The CT mechanism and properties are considered in close connection with the thin film microstructure of the D/A blends which can be controlled via a change of the molecule geometry and/or growth temperature. We discuss two key findings for our systems: (1) The CT intensity correlates directly with the possibility of cocrystallization between acceptor and donor. (2) Side chain modification to tune the ground state energy levels has nearly no effect on the energy of the excited state CT, whereas replacement of molecular core modifies the CT energy correspondingly.