Hyperbranched Crystalline Nanostructure Produced from Ionic π-Conjugated Molecules
We synthesized the first hyperbranched crystalline nanostructure form ionic organic molecules. Recently, much effort has been focused in synthesis of complex 3D hierarchical crystalline assemblies since the enlarged specific surface area is advantageous for enhanced performance of sensors and catalysts where the number of active sites scales with the available surface area. For high efficiency of solar to electrical energy conversion, the high surface to volume ratio of nanostructured electrodes provides short electrical pathways for rapid transport. Branched nanostructures with extensive connectivity have been fabricated from inorganic semiconductors, primarily metal oxides and chalcogenides. 3D branched or dendridic conductive polymers are also known and can be prepared with high regularity and controlled molecular weights but their morphology is not always well defined. We have built the first crystalline hyperbranched 3D nanostructure fabricated from ionic organic molecules, porphyrins, TAPP:TSPP. These have well-defined sheaf-like morphology that structurally resembles the hyperbranched nanoarchitectures made from inorganic semiconductors (e.g. α-Fe2O3, α-GaOOH, and Bi2S3). The hierarchical sheaf-like growth of the assemblies exhibits Arrhenius behavior. The observed morphology results from crystal splitting during initial oriented attachment growth followed by Ostwald ripening.
Time dependent growth of TAPP:TSPP nanoribbons (L1/2) versus time (sec) fit to the LSW classical kinetic model for crystal coarsening. Fits for different values of n are shown for n = 2 (dotted line), n = 3 (solid line), n = 4 (dashed line).