Pseudomorphic transformation in nanostructured thiophene-based materials

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 post-oxidation 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 exhibit 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.