Fluorescent dyes with a high sensitivity of their optical spectra towards changes of the
environment were prepared via aldol condensation or Horner olefinations. The main chromophore
is a quadrupolar N-substituted 1,4-distyrylbenzene which allows protonation and complexation at
various positions resulting in a series of different and significant changes of the optical spectra. The
sensitivity of the absorption and emission spectra on solvent polarity, acid, and cations is reported.
The title compound, C12H9ClN4, was prepared from dichloropyridazine and tolyltetrazole in a nucleophilic biaryl coupling followed by thermal ring transformation. The molecule is essentially planar (r.m.s. deviation for all non-H atoms = 0.036 Å) and an intramolecular C—H⋯N hydrogen bond occurs. In the crystal, the molecules form dimers connected via π–π interactions [centroid–centroid distance = 3.699 (2) Å], which are further connected to neighbouring molecules via C—H—N bonds. The bond lengths in the pyridazine ring system indicate a strong localization of the double bonds and there is a weak C—Cl bond [1.732 (3) Å].
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