Molecular recognition of organic dyes in aqueous environments using prismarene hosts

In 2020, Prof. Gaeta introduced a new class of macrocyclic hosts named prism[n]arenes [1], consisting of 1,5-methylene-bridged naphthalene units characterized by a deep π-electron rich cavity. Water-soluble carboxylate-primaries [2] (PrS[n]COO), exhibit special recognition properties in water, such that in the medium the formation of endo-cavity complexes is driven by C−H···π interactions and by the hydrophobic effect. These prismarenes have already attracted much interest in the scientific community, moreover, research groups are exploiting the structural and supramolecular properties of prismarenes for very interesting applications [3,4]. Prismarenes exhibit an S0-S1 transition peaking at ca. 350 nm in UV-Vis spectra and emit blue-violet light at 390 nm with a moderate quantum yield of Φ = 0.10. Prismarene macrocycles exhibit a significant cavity, which is modulated based on the macrocycle size, i.e. the number (n) of arene units used, which is usually indicated in the name of prisma[n]arenes. Furthermore, prismarenes exhibit planar chirality and are dynamically racemic [1,2] through rapid interconversion of enantiomers by rotation of aromatic units. Prismarene macrocycles exhibit very specific structural and supramolecular properties, which make them promising candidates for host-guest complexation of organic dyes such as Rhodamine B or Methylene Blue in aqueous buffer solution. The results of UV-Vis titrations indicate the formation of prismarene[6]sulfate and dye complex (Figure1), and the association constant has been calculated by using the inferred equation. Also, the possible mechanism of molecular interaction will be discussed in the meantime