Synthesis and complexation behavior of diaza-18-crown-6 carrying two pyrenylmethyl groups

N,N'-Bis(1-pyrenylmethyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (1) and N-(1-pyrenylmethyl)-1,4,7,10,13-pentaoxa-16-azacyclooctadecane (2) were synthesized and found to display unique photophysical properties in the presence of the guest-metal salts. The binding of metal ions to the diazacrown ether 1 cavity inhibited the exciplex formation and changed the distance between two pyrenyl groups. This caused not only an emission-intensity enhancement, but also a large change in the monomer/excimer fluorescence-intensity ratio. The change resulted from the coordinated structure and exchange process between the free host 1 and its metal salt complex in the ground state.