Leveraging the Assembly of a Rylene Dye to Tune the Semiconducting Properties of Functionalized n-Type, Hybrid Si Interfaces.

Abstract

The functionalization of silicon electrodes with π-conjugated chromophores opens new avenues to engineer hybrid semiconducting interfaces relevant to information storage and processing. Notably, molecularly dissolved π-conjugated units, such as ferrocene derivatives, are traditionally exploited as building blocks to construct well-defined interfaces that establish electrochemically addressable platforms with which to investigate electron transfer properties and charge storage capabilities. In contrast, planar π-conjugated building blocks such as naphthalene diimide (NDI) cores enable the formation of solvated aggregates equipped with emergent electronic structures not manifested by the parent, molecularly dissolved building blocks. To interrogate the extent to which the aggregated states of π-conjugated chromophores can be leveraged to regulate the n-type semiconducting properties of functionalized electrodes, we have devised an amphiphilic rylene core (NDI) that demonstrates a non-negligible degree of aggregation in an aqueous medium. Characterization of the electronic structures of the NDI-derived aggregates using a combination of electrochemistry, reductive titration experiments, and spectroelectrochemistry unveils the existence of π-anion stacks, the formation of which is contingent on the initial concentration of NDI building blocks. We show that grafting n-doped NDI aggregates on silicon electrode precursors equipped with a high density of anchoring groups by means of "click" reaction enables the formation of the hybrid Si-NDI electrode (Si-NDI-15@1) that facilitates electron injection by more than 400 mV when compared to Si interfaces constructed from molecularly dissolved NDI units. Furthermore, the engineering of a Si precursor surface characterized by a low density of anchoring groups provides additional proof to highlight that the potentiometric properties recorded for Si-NDI-15@1 originate from NDI units, evidencing a non-negligible degree of aggregation. The present work delivers tools to manipulate the potentiometric properties of functionalized electrodes by leveraging on the electronic structures of aggregated, π-conjugated precursors.