Synthesis, crystal structure, and spectroscopic properties of new stilbazolium salt with enlarged π-conjugated system

A new stilbazolium dye 4-{(E)-2-[4-(dimethylamino)naphthalen-1-yl]ethenyl}-1-methylquinolinium iodide monohydrate (DANSQI) having enlarged π-conjugated system was synthesized and characterized by X-ray diffraction, IR, Raman, UV–Vis, Fluorescence, 1H- and 13C NMR spectroscopy. Quantum chemical calculations were performed to obtain electronic structure and vibrational data, using DFT. The crystals are monoclinic, space group P21/n, with a = 8.0751(14), b = 25.839(4), c = 10.9031(15) Å, V = 2141.4(6) Å3, and Z = 4 (at 300(2) K). The unit cell contains four molecules of the dye, participating in weak intermolecular interactions. The cation is nearly flat with a deviation of the planarity of 5.08 (1)°. The dye investigated is the first stilbazolium iodide containing water molecule in the solid state therefore the N-dimethylamino group declines significantly from planarity, as indicated by C13N1C2C3 torsion angle of 16.08°. The dye studied shows solvatochromism of 84 nm in visible region and very large Stokes shift up to 253 nm. The intensity of fluorescence bands strongly depends on solvent polarity.

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► New stilbazolium dye was synthesed.
► Single crystal X-ray analyses was performed and the structure was solved.
► The dye was investigated by IR, Raman, UV–Vis, Fluorescence, and NMR spectroscopy.
► We report the highest Stocks shift known up to now for stilbazolium dyes.
► We note a discrete structure of fluorescent spectra in polar solvents.