C64 Nanographene Tetraimide—A Receptor for Phthalocyanines with Subnanomolar Affinity

Abstract

Phthalocyanines are extensively used by the dye and pigment industry and in photovoltaic and photodynamic therapy research due to their intense absorption of visible light, outstanding stability, and versatility. As pigments, the unsubstituted phthalocyanines are insoluble owing to strong intermolecular π-π-stacking interactions, which causes limitations for the solution chemistry for both free base and metalated phthalocyanines. Here we show a supramolecular host–guest strategy to dissolve phthalocyanines into solution. C64 nanographene tetraimide (1) binds two free base/zinc/copper phthalocyanines in a 1 : 2 stoichiometry to solubilize phthalocyanines as evidenced by 1H NMR spectroscopy, UV/Vis absorption and single-crystal X-ray analysis. Binding studies using a tetra-tert-butyl-substituted soluble phthalocyanine revealed binding affinities of up to 109 M−1 in tetrachloromethane, relating to a Gibbs free energy of −52 kJ mol−1. Energy decomposition analysis revealed that complexes between 1 and phthalocyanines are stabilized by dispersion interactions followed by electrostatics as well as significant charge-transfer interactions.