Lower Rim Naphthyl-Functionalized Resorcin[4]arene Conformers: Column Chromatographic Separation and Adaptive Molecular Recognition.

Conformational bias plays a crucial role in host-guest complex. Due to spatial arrangements of binding sites, binding affinities of conformers differ significantly toward a guest. Consequently, isolation of conformers is a prerequisite in understanding host-guest complexes. Herein, we report the synthesis and separation of naphthalene-functionalized resorcin[4]arenes in two distinct conformations: chair and crown. The use of bulky naphthalene as a pendant at methylene bridge results in steric strain, yielding conformationally nonconvertible isomers, with large difference in dipole moment (Δμ = 6.83 D), facilitating their separation by traditional column chromatography. The isomers were characterized by NMR, mass, and X-ray diffraction analysis. Notably, in polar solvent, the crown isomer undergoes a conformational change to boat, in the upper rim, coupled with rotation of naphthalene in the lower rim. The solvent-dependent conformational and rotational change results in an electron-rich cavity in the lower rim in nonpolar solvent that binds with electron-deficient nitroaromatics. While the incorporation of naphthalene in the lower rim overcomes the bottleneck of separation of distinct conformers, the conformation-specific binding in the lower rim diversifies its applications beyond cation binding and paves a new direction in hosting guests in the lower rim which remained underexplored so far.