Molecular recognition of polymethoxybenzenes by host molecule comprised of two pyromellitic diimides and two dialkoxynaphthalenes

For the continuing study of the molecular recognition of the π-electron-poor host comprised of two pyromellitic diimides and two dialkoxynaphthalenes, its inclusion with π-electron-rich polymethoxybenzenes has been examined. The UV–vis titration studies indicated following order of the association constants (Kaʹs) as 1:1 complexes in CHCl3: 1,3,5-trimethoxybenzene (31.3 M−1)>1,3-dimethoxybenzene (9.2 M−1)>1,2-dimethoxybenzene (6.5 M−1)>1,4-dimethoxybenzenes (2.8 M−1). The X-ray structural analysis of the complexes between the host and dimethoxybenzenes proved the intracavity 1:1 complexes and provided useful information on the structures of the complexes. Not only charge transfer interactions but also other weak interactions such as electrostatic, van der Waals, and the unique hydrogen bonds between the α-hydrogen atoms of the naphthalene and the methoxy oxygen atoms were considered to be responsible for the magnitude of the Kaʹs. Thus molecular recognition of polymethoxybenzenes has been accomplished by the neutral host using multipoint weak interactions in an organic solvent.