Pseudomorphic Transformation in Nanostructured Thiophene-Based Materials.

Abstract

This study reveals the capability of nanostructured organic materials to undergo pseudomorphic transformations, a ubiquitous phenomenon occurring in the mineral kingdom that involves the replacement of a mineral phase with a new one while retaining the original shape and volume. Specifically, it is demonstrated that the postoxidation process induced by HOF·CH₃CN on preformed thiophene-based 1D nanostructures preserves their macro/microscopic morphology while remarkably altering their electro-optical properties by forming a new oxygenated phase. Experimental evidence proves that this transformation proceeds via an interface-coupled dissolution-precipitation mechanism, leading to the growth of a porous oxidized shell that varies in thickness with exposure time, enveloping the pristine smooth core. The oxygenated species exhibits stronger electron-acceptor characteristics than the core material, promoting charge transfer state formation, as confirmed by microspectroscopy and DFT calculations. This enables (i) precise modulation of the nanostructure's surface potential, allowing for the formation of entirely organic heterojunctions with precise spatial resolution via wet chemical processing; (ii) effective doping of the nanostructure, resulting in a strong change of the conductivity temperature dependence and a switch between a low and high conduction state depending on the applied bias. Overall, this work showcases an approach to engineering "impossible" composite architectures with pre-established morphology and tailored chemical-physical properties.