Heteroassociation of the bromine-containing anions of sulfophthaleins in aqueous solution

Abstract

The ability of bromine-containing anions of sulfophthalein dyes, such as bromophenol blue (BPB), bromocresol green (BCG), bromocresol purple (BCP), bromothymol blue (BTB), as well as non-substituted phenol red (PhR), to form heteroassociates in aqueous solution was investigated. Singly and doubly charged anions BPB, BCG, BCP, BTB, and PhR (HAn-, An2-) are capable of forming stable heteroassociates of composition Ct+•HAn- and (Ct+)2•An2- with cationic polymethine dyes (Ct+), such as pinacyanol and quinaldine red. The enthalpies of formation of the dye ions and heteroassociates were calculated by semiempirical methods, and the most probable structure of heteroassociates was determined.