Facile Synthesis of Pyrrolyl-Containing Semisquaraines in Water as Precursors for Non-Symmetric Squaraines

Abstract

One-step reactions between squaric acid and pyrroles, such as 3-ethyl-2,4-dimethyl-pyrrole and 1,2,5-trimethylpyrrole, in water provide the corresponding pyrrol-2-yl- and pyrrol-3-yl-containing semisquaraines in high yields. These semisquaraines serve as useful precursors for the synthesis of various non-symmetric pyrrole-containing squaraine dyes.