Synthesis and crystal structure determination of 2,6-di-tert-butyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate and its corresponding perchlorate salt

2,6-Di-tert-butyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate belongs to the class of negatively solvatochromic dyes commonly used for the empirical determination of solvent polarities. By way of exception, it crystallizes without any solvent of crystallization due to the presence of two bulky tert-butyl groups in the phenolate moiety. The synthesis of this hydrophobic betaine dye has been improved and an X-ray crystal structure analysis of this solventless zwitterionic dye and its protonated form (as a perchlorate salt) has been carried out.

► The di-tert-butyl-substituted betaine dye crystallizes without any solvent.
► Protonation of the di-tert-butyl-substituted betaine dye only marginally changes the geometry.
► The perchlorate salt of the di-tert-butyl-substituted betaine dye cation doesn’t form an intermolecular H2O⋯H–O bond.
► The di-tert-butyl-substituted betaine dye is a much stronger base in solution, than other pyridinium-N-phenolate dyes.