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

Linear exo-endo polymeric chain structures of Zn2DEP with longer bidentate substrates are reported. The role of size and nature of the substrates in controlling the design of the axially coordinated complexes has been demonstrated. Pyrrole-bridged Zn(II) porphyrin dimer, Zn2DEP, 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 Zn2DEP 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.

Automated summary

This study reports the linear exo-endo polymeric chain structures of Zn2DEP with longer bidentate substrates, and demonstrates the role of substrate size and nature in controlling the design of axially coordinated complexes. Zn2DEP has been shown to act as an efficient tweezer host for binding different guests inside its cavity, forming discrete monomeric, sandwich, and polymeric complexes based on the size and type of axial guests. This work can contribute to the rational design of receptors for molecular recognition and chirality sensing devices.