Synthesis and unusual response to potassium of bipyridinium-benzocrown ether conjugate

A bipyridinium derivative appending a benzocrown ether, in which the phenyl unit in the benzocrown ether was directly bounded to the N-position of the bipyridinium unit, has been synthesized. The compound showed a yellow color associated with an intramolecular charge transfer (CT), which was affected by the presence of alkali and alkaline earth metal ions. An unusual CT response to K⁺ for 1 was observed and could be applicable for K⁺ sensing.