Two red salts derived from yellow 4-cyano-1-methylpyridinium iodide: 1,1′,1″-trimethyl-4,4′,4″-(1,3,5-triazin-2,4,6-triyl)tripyridinium trisiodide and 4-cyano-1-methylpyridinium triiodide

Inclusion and Charge Transfer Interaction of a Multi-Redox Active 1,3,5-Triazine Derivative by Cucurbit[7,8]urils

The redox active 1,3,5-triazine derivative (MPT) was used as a guest to study host-guest, charge transfer interaction with CB[7,8] in water. The multi-redox active MPT undergoes four chemically and electrochemically reversible one electron redox states in organic media, but in water, the fourth redox state shows an unstable nature. As a guest, the host-guest interaction of MPT was studied with two macrocyclic cucurbit[7,8]uril (CB[7,8]) hosts in water; resulting supramolecular complexes were characterized by NMR, ESI-MS, UV-vis, ITC, and cyclic voltammetric studies.

A mutually stabilized host-guest pair

By using click chemistry, a hexacationic cage was synthesized. The cage contains two triscationic π-electron-deficient trispyridiniumtriazine (TPZ³⁺) platforms that are bridged in a face-to-face manner by three ethylene-triazole-ethylene linkers. A diversity of π-electron-rich guests can be recognized within the pocket of the cage, driven by host-guest π-π interactions. The cage cavity acts as a protecting group, preventing an anthracene guest from undergoing Diels-Alder reaction. Under ultraviolet (UV) light, the pyridinium C─N bonds in TPZ³⁺ platforms are polarized and weakened, resulting in the occurrence of cage decomposition via β-elimination. Guest recognition could help to prevent this UV-stimulated cage decomposition by suppressing the excitation of the TPZ³⁺ units.