title: Halochromic and hydrochromic squaric acid functionalized perylene bisimide.
abstract: The functionalization of perylene bisimide by squaric acid afforded halochromic dyes with pronounced acidity. The dye senses solvent polarity, pH and humidity by means of pronounced changes in absorption spectra and thin film color through the intramolecular charge transfer between perylene and cyclobutene cores initiated by protonation/deprotonation.
authors.affiliation: Universität Würzburg, Institut für Organische Chemie and Center for Nanosystems Chemistry, Am Hubland, 97074 Würzburg, Germany. wuerthner@chemie.uni-wuerzburg.de.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Maeda
authors.forename: Frank
authors.initials: F
authors.lastname: Würthner