Pyridinium N‐Phenolate Betaine Dyes and Their Application to the Characterization of the Polarity of Solvents, XXII. Syntheses and UV/Vis Spectroscopic Properties of Solvatochromic, Halochromic, and Chiro‐Solvatochromic Pyridinium N‐Phenolate Betaine Dyes with Four Stereogenic Centers

Abstract Syntheses (Schemes 1–3), negative solvatochromism (Table 1), cation‐induced negative halochromism (Table 2), and chiro‐solvatochromism (Tables 3 and 4) of the new crown ether‐substituted chiral pyridinium N‐phenolate betaine dyes 18a, b and 28a, b, each posessing four stereogenic centers, are described. The absolute configuration at the four stereogenic centers of the chiral betaine dyes has been confirmed by X‐ray crystal structure analysis of the intermediate phenol 14a (Figure 1). Solutions of the chiral betaine dyes 18a, b and 28a, b, prepared by addition of monochiral amines and amino alcohols to solutions of the salts 17a, b and 27a, b in ethanol, exhibit in some cases small but significant chirosolvatochromic band shifts of up to Δλ = 10–12 nm (Tables 3 and 4), caused by chiral recognition of the monochiral guest molecules.