Adsorption Structures Affecting the Electronic Properties and Photoinduced Charge Transfer at Perylene-Based Molecular Interfaces

Perylene-based organic semiconductors are widely used in organic electronic devices. Here, we studied the ultrafast excited state dynamics after optical excitation at interfaces between the electron donor (D) diindenoperylene (DIP) and the electron acceptor (A) dicyano-perylene-bis(dicarboximide) (PDIR-CN2) using femtosecond time-resolved second harmonic generation (SHG) in combination with large scale quantum chemical calculations. Thereby, we varied in bilayer structures of DIP and PDIR-CN2 the interfacial molecular geometry. For an interfacial configuration which contains a edge-on geometry but also additional face-on domains an optically induced charge transfer (CT) is observed, which leads to a pronounced increase of the SHG signal intensity due to electric field induced second harmonic generation. The interfacial CT state decays within 7.5 & PLUSMN;0.7 ps, while the creation of hot CT states leads to a faster decay (5.3 & PLUSMN;0.2 ps). For the bilayer structures with mainly edge-on geometries interfacial CT formation is suppressed since & pi;-& pi; overlap perpendicular to the interface is missing. Our combined experimental and theoretical study provides important insights into D/A charge transfer properties, which is needed for the understanding of the interfacial photophysics of these molecules.

Automated summary

By combining femtosecond time-resolved second harmonic generation (SHG) with large scale quantum chemical calculations, we studied the ultrafast excited state dynamics at interfaces between diindenoperylene (DIP) and dicyano-perylene-bis(dicarboximide) (PDIR-CN2). Our results showed that an optically induced charge transfer (CT) is observed in the configuration with edge-on geometry and additional face-on domains, resulting in an increase in SHG signal intensity. The interfacial CT state decays within 7.5±0.7 ps, while the creation of hot CT states leads to a faster decay (5.3±0.2 ps). The formation of interfacial CT is suppressed in bilayer structures with mainly edge-on geometries due to the lack of π-π overlap perpendicular to the interface. Our study provides important insights into the D/A charge transfer properties and the interfacial photophysics of these molecules.