Non-Covalent Assembly and Control of Charge Transport in Ultrathin Films Based on Graphene Oxide and Organic Chromophores

A new strategy of controlled non-covalent assembly is applied for tuning of the properties of ultrathin film hybrids based on graphene oxide (GO), tetracarboxyphenylporphyrin (TCPP), and polydiacetylene surfactant (PDA). It is shown how, using layer-by-layer deposition or one-step self-assembly of components at the air/water interface, it is possible to influence the mechanisms of energy and charge transfer while maintaining the chemical composition of the ultrathin film. Zinc acetate was used to integrate the active components of the hybrid through coordination bonds with the carboxyl groups of the GO and organic components. Atomic force microscopy showed that layer-by-layer assembly results in an ordered structure with a dense monolayer of GO at the base, an intermediate layer of TCPP, and an upper layer of PDA crystallites. Single-stage assembly leads to the formation of a mixed layer of GO–Zn2+–TCPP with a folded GO morphology covered with PDA. Spectroscopic studies revealed Förster resonance energy transfer in both hybrids, in which porphyrin acts as both an energy donor and acceptor depending on the structural form of the polydiacetylene surfactant associated with it. Hybrids obtained by layer-by-layer assembly, when integrated into photovoltaic cells with an electron-hole transport layer, demonstrated pronounced diode properties and significant photoresponse due to effective spatial separation of charges and directed transport in the layered structure. Hybrids obtained in a single stage produce symmetrical volt-ampere curves and low photoresponse due to exciton recombination in a disordered structure. The results demonstrate the fundamental possibility of controlling charge transport in photoactive hybrids by controlling their supramolecular organization through the choice of assembly method.