Microreview: Pyrrol‐3‐yl squaraines (including indol‐3‐yl squaraines)

Abstract

Pyrrol‐3‐yl squaraine dyes are prepared by the condensation of 3,4‐dihydroxycyclobut‐3‐ene‐1,2‐dione with two‐molar equivalence of a 2,5‐disubstituted pyrrole possessing a free β‐position, or substituted indoles with a similarly free β‐position. From the first reported syntheses of two indol‐3‐yl squaraines in 1966, numerous pyrrol‐3‐yl squaraines (including indol‐3‐yl squaraines) have been reported in both the scientific and patent literatures. This microreview highlights the synthesis, history, spectroscopy, and applications of pyrrol‐3‐yl squaraines from their first preparation to the present date.

Síntesis de bis(indolil)escuaraínas

“…Las reacciones laterales indeseadas son notorias en la formación de bis(indolil)escuaraínas. (Lynch, 2018) y por esta razón se probaron diferentes técnicas de aislamiento que se describen a continuación.…”

“…En este sentido, las escuaraínas son moléculas privilegiadas porque presentan intensa fluorescencia por la absorción de dos fotones de radiación visible o infrarroja. A pesar del excelente carácter donador del indol los ejemplos de bis(indolil)escuaraínas reportados en la literatura aún son escasos (Sun, 2015;Lynch, 2018) en comparación a otros tipos de escuaraínas. (Beverina, 2009).…”

Accessing Symmetrical Tetraphenyl‐pyrrole‐2‐yl Squaraines Through an Improved Synthesis of 2,4‐Diphenylpyrrole

“…The discovery of squaraine dyes in 1965 made by Triebs and Jacob, who reported formation of an insoluble product when pyrrole was reacted with squaric acid, sparked a vivid interest in this class of organic molecules . Soon, a plethora of literature reports accompanied by an overwhelming number of patent applications appeared, pointing to the importance of squaraine dyes in fundamental research and their potential for high‐tech applications . Owing to their advantageous and tunable photophysical properties squaraine dyes have been considered as photosensitizers for photodynamic therapy (PDT) .…”