Stilbene and Azobenzene Diazonium Compounds as dye reagents for crown ethers

The change of light absorption of six coloured diazonium compounds (1, 2a, 2b, 3, 4, 5) on complexation with five 18-crown-6 derivatives (6–10) in 1,2-dichloroethane was investigated. In the benzene, stilbene and azobenzene series complexation produces only hypsochromic shifts of the intramolecular ct-band of the diazonium ions up to 140 nm. The extend of the shift is effected by ion pairing. The ct-transition energy of the complexes diazonium ion is independent on the present anion in contrast to the uncomplexed compounds. The colour changes are not caused by host to guest charge transfer or E/Z-isomerisation of the stilbene and azobenzene derivatives. A quantitative explanation of the colour changes is given basing on an electrostatic interaction model.