N.N ' -Bis(tropon-2-yl)diazacrown ethers (2) were found to display unique absorption spectral changes in the presence of guest cations. X-ray crystallographic analysis indicated that 2a . zinc and 2c . calcium thiocyanate complexes consist of an ion pair with zinc tetrathiocyanate anion and 2a . zinc cation, and with calcium hexathiocyanate anion and 2c .H2O . calcium cation, respectively. Complexation gave rise to deconjugation between the tropone ring and the lone pair electrons of the nitrogen atom to cause spectral changes.