Metal-mediated self assembly of tetrapyridyl porphyrins by Na+ ions

The formation of nanostructured, porphyrin-based films have widely attracted the interest due to their potential applications in sensing, optoelectronics and catalysis.1 Among porphyrins, meso-pyridyl derivatives are largely used as tectons in coordination-driven self-assembly, forming very complex organic-inorganic supramolecular structures.2 In this work, we investigate the spontaneous formation of new porphyrin-based films driven by the coordination of sodium ions, which can be dissolved in CH2Cl2 as countercations of the bulky tetrakis[3,5-bis(trifluoromethyl) phenyl]borate (NaTPFB) anion, by the N atoms present at the meso position of the tetra(4-pyridyl)porphyrin (TPyP(4)). The reactivity toward Na+ has been examined also for TpyP(4) metallo-derivatives containing Cu(II), Zn(II) and Mn(III) ions and, again, self-assembled nanostructures have formed on surface, displaying long-range order and tuneable optical and morphological features. In particular, both the free base and Cu(II) derivative form 2D objects, whereas the other two metallo-porphyrins lead to elongated structures with very high aspect ratios. These differences might be related with the first two molecules being similarly flat (Cu(II) adopts a square planar coordination geometry when included in the porphyrin ring), whereas Zn(II) and Mn(III) bind one and two axial ligands, respectively, to satisfy their coordination requirements.3 This approach may allow to obtain new functional architectures of potential interest in optoelectronics or photonics, as well as to devise new strategies in the design of supramolecular materials.