Design and control of axial binding with flexible Zn(II) porphyrin dimer: Building-up novel polymer with exo–endo binding

Pyrrole-bridged Zn(II) porphyrin dimer, Zn 2 DEP, has been utilized as an efficient tweezer host for the binding of guest (substrate) inside the cavity due to its large vertical flexibility. Aromatic monodentate substrate binds in an exo−endofashion to form a discrete monomeric complex while it converts to anexo−exo upon increasing the bulk of the guest. Shorter bidentate guest, on the other hand, forms 1:1 sandwich complex. In contrast, a longer bidentate guest binds in an exo−endo fashion but to form a polymeric structure. The complexes have been isolated in the solid state and structurally characterized while their complexation process in solution has been monitored spectroscopically. We also provide here a comprehensive account of the substrate binding ability of flexible Zn 2 DEP towards preferential formation of discrete monomeric exo–endo, exo–exo and sandwich complexes as well as 1D polymer just upon varying the size and type of axial guests. This work can contribute towards the rational design of receptors as highly efficient probes for molecular recognition and chirality sensing devices.