Colour Change of 4‐Diethylamino‐α‐cyano‐stilbene‐4‐diazonium Ions by Complex Formation with Ethylenglycol Derivatives, Crownethers and ValinomycineThe formation and light absorption of complexes consisting of coloured stilbene‐4‐diazonium ions and different ethylenglycoles, crownethers and valinomycine were investigated. On complex formation the longest wavelength absorption band of the diazonium compounds shifts hypsochromically. This hypsochromism is solvent dependent. The difference between the absorption maximum of a free and complexed diazonium ion increases with increasing polarity and decreasing n‐donicity of the solvents. Other complex forming cations are able to replace the diazonium ions in the complexes, whereby the colours of the original diazonium ions are regenerated. These colour changes can be used to indicate the ability of n‐donor compounds to act as an ionophore.

Light Absorption and Substituent Effects of Stibene‐4‐diazonium Ions Substituent effects on ṽmax‐values of 31 stilbene‐4‐diazonium ions are studied. With increasing donor strength of a substituent in 4′‐position the long wave absorption band of stibene‐4‐diazonium ions shifts from the ultraviolet to the red region of the spectrum. The particular deep colour of diazonium compounds may be described by the very high σp‐Hammett‐constant of the diazonium group. The substituent effects found characterize stilbene diazonium ions as typical donor‐acceptor chromogenes.

Solvatochromism of 4′‐Dialkylamino‐α‐Cyano‐Stilbene‐4‐Diazonium‐Salts 4′‐Dialkylamino‐stilbene‐4‐diazonium‐salts are deep coloured compounds and give strong solvatochromism. 4′‐Diethylamino‐α‐cyano‐stilbene‐4‐diazonium‐tetrafluoroborate was investigated in 52 different solvents and 3 binary solvent mixtures. With increasing solvent basicity the longest wave lenght absorption maximum (\documentclass{article}\pagestyle{empty}\begin{document}$ \nu^{\hspace{-5pt}\sim}_{\rm max} $\end{document}) decrease. Complex formation by crown ethers causes a decrease of \documentclass{article}\pagestyle{empty}\begin{document}$ \nu^{\hspace{-5pt}\sim}_{\rm max}$\end{document}, too. In solvents with dielectricity constants higher than about 15 dissociation effects superpose solvatochromism. The summary of experimental dates support the approach of specific nucleophilic solvatation of diazonium ions.

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.

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