title: Anthryl-substituted heterocycles as acid-sensitive fluorescence probes.
abstract: [reaction: see text] Four pH-sensitive fluorescence probes are presented which consist of an anthracene fluorophore and a pi-conjugated oxazoline, benzoxazole, or pyridine substituent. The protonation of the heterocycles increases their acceptor properties and results in significant red-shifts of the absorption and emission maxima of the anthracene chromophore. The comparison between 2-[2'-(6'-methoxyanthryl)]-4,4-dimethyl-2-oxazoline and 2-[2'-(anthryl)]-4,4-dimethyl-2-oxazoline reveals that the donor-acceptor substitution pattern of the fluorophore is not required to achieve a red shift upon protonation. The benzoxazole and pyridine substituents offer a particular advantage due to their persistence under acidic conditions. Thus, these compounds may be used as efficient pH-sensitive fluorescence switches. Nevertheless, the switching of benzoxazole 2c requires relatively strong acidic conditions. The anthrylpyridinium exhibits a red-shifted emission in chloroform; however, it is nonfluorescent in aqueous or alcoholic solution. Although the oxazoline is not persistent under permanent acidic conditions, this heterocycle may be useful as a substituent in fluorescence indicators since it may be used to detect acid concentrations of 10(-4)-10(-5) M, which are close to the biologically relevant range.
authors.affiliation: Institut für Organische Chemie, Universität Siegen, Adolf-Reichwein-Str., D-57068 Siegen, Germany. ihmels@chemie.uni-siegen.de
authors.forename: Heiko
authors.initials: H
authors.lastname: Ihmels
authors.forename: Andreas
authors.initials: A
authors.lastname: Meiswinkel
authors.forename: Christian J
authors.initials: CJ
authors.lastname: Mohrschladt
authors.forename: Daniela
authors.initials: D
authors.lastname: Otto
authors.forename: Michael
authors.initials: M
authors.lastname: Waidelich
authors.forename: Michael
authors.initials: M
authors.lastname: Towler
authors.forename: Rick
authors.initials: R
authors.lastname: White
authors.forename: Martin
authors.initials: M
authors.lastname: Albrecht
authors.forename: Alexander
authors.initials: A
authors.lastname: Schnurpfeil