Hydrogen-Bonding and Pi-Stacking Induced Self-Assembly of Picolinic Acid-Substituted Phthalocyanine Derivatives

The preparation of organic-based, supramolecular architectures which present a high degree of order spanning from the nanoscopic to the macroscopic level across multiple length scales is highly desirable and represents a key issue within the fast-growing fields of nanoscience and nanotechnology.^[1] In this context, self-assembly appears as an attractive and efficient strategy for the construction of such ordered structures as it can allow the preparation of complex, (multi)functional systems in an efficient and controlled way.^[2] Among the organic compounds used for this purpose, π-conjugated systems such as phthalocyanines (Pcs),^[3] aromatic macrocycles featuring unique structural, optical and redox properties,^[4] are ideal candidates due to their excellent self-organization ability.^[5]

We present here a new family of picolinic acid-terminated Pcs (1-3, Figure 1) which are able to self-aggregate in different solvents giving rise to the formation of columnar H-aggregates as a result of a combination of π-π supramolecular interactions between the Pc macrocycles and hydrogen bonding interactions between the terminal picolinic acid moieties.^[6] Remarkably, the assembly/disassembly of these supramolecular systems can be reversible controlled by the addition of acids or bases to the Pc solutions. In Pc 3, chiral alkoxy units have been introduced at the Pc peripheral positions with the aim of influencing the stacking of the H-aggregates towards the formation of single-handed columnar structures.

References

1.   Special issue on “Supramolecular approaches to organic electronics and nanotechnology”. Adv. Mater. 2006, 18, 1227-1329.

2.   Special issue on “Supramolecular chemistry and self-assembly”. Science 2002, 295, 2395-2421.

3.   G. de la Torre, C.G. Claessens, T. Torres Chem. Commun. 2007, 2000-2015.

4.   G. Bottari, G. de la Torre, D. M. Guldi, T. Torres Chem. Rev. 2010, 110, 6768-6816.

5.   G. Bottari, J. A. Suanzes, O. Trukhina, T. Torres J. Phys. Chem. Lett. 2011, 2, 905-913.

6.   Manuscript in preparation.