A styryl dye with a chromophore based on methyl-benzothiazolium and 1-methyl-4-phenylpiperazine end group was synthesized under new improved reaction conditions. The synthesis was carried out in a way that ensured the direct production of a pure (>98 %) dye. The dye exhibits pronounced vertical and horizontal solvatochromism in both light absorption and fluorescence spectra. In the UV–Vis spectra of the dye, a difference in the longest wavelength absorption maximum from dichloromethane to water of about 100 nm was observed. In buffer (pH = 7.2), the dye absorbs at 445 nm, and in dichloromethane at 547 nm. The interaction of the dye with DNA and with protons and various metal ions was investigated, and the ability of the target fluorochrome to be used as a logic gate in the simultaneous presence of H⁺ and DNA was demonstrated. The dye is sensitive in the presence of mercury ions as well.