Synthesis, Solid-State Analyses, and Anion-Binding Properties of meso-Aryldipyrrin-5,5′-diylbis(phenol) and -bis(aniline) Ligands

The design of new molecular scaffolds for the selective recognition or transport of anions is often critical, because subtle changes in the substitution pattern may drastically impact the targeted properties. Herein, detailed spectroscopic and X-ray crystal-structure analyses were used to investigate the effect of the substitution pattern of a new series of N2O2 or N-4 anion sensors. Our study evidences two distinct in-in and in-out conformations depending on the nature of the substituent (e. g., phenol vs. aniline). Interestingly, because of intramolecular hydrogen bonds involving the -OH or the -NH2 functions, the dipyrrin subunit only acts as a scaffold and does not participate in the anion binding. Furthermore, the nature of the meso substituent was not critical, as similar binding affinities were measured for meso-C6H5 or meso-C6F5 ligands. Hence, the meso position can be further modified without any noticeable changes to the electron density on the dipyrromethene subunit.