pH-Sensitive Fluorescence Switching of Pyridylanthracenes: The Effect of the Isomeric Pattern

Abstract

9,10-substituted anthracenes are known for their useful optical properties like fluorescence, which makes them frequently used probes in sensing applications. In this article, we investigate the fundamental photophysical properties of three pyridyl-substituted variants. The nitrogen atoms in the pyridinium six-membered rings are located in the ortho-, meta-, and parapositions in relation to the anthracene core. Absorption, fluorescence, and transient absorption measurements were carried out and were complemented by theoretical calculations. We monitored the photophysics of the anthracene derivatives in chloroform and water investigating the protonated as well as their nonprotonated forms. We found that the optical properties of the nonprotonated forms are strongly determined by the anthracene chromophore, with only small differences to other 9,10-substituted anthracenes, for example diphenyl anthracene. In contrast, protonation leads to a strong decrease in fluorescence intensity and lifetime. Transient absorption measurements and theoretical calculations revealed the formation of a charge-transfer state in the protonated chromophores, where electron density is shifted from the anthracene moiety toward the protonated pyridyl substituents. While the para-and ortho-derivatives' charge transfer is still moderately fluorescent, the meta-derivative is affected much stronger and shows nearly no fluorescence. This nitrogen-atom-position-dependent sensitivity to hydronium activity makes a combination of these fluorophores very attractive for pH-sensing applications covering a broadened pH range.

Amphiphilic Asymmetric Diblock Copolymer with pH-Responsive Fluorescent Properties

“…Stimuli-responsive copolymers that can respond to external stimuli or changes in the surrounding environment, , for example, pH, , temperature, , light, − magnetism, and other types, to make adaptable changes have aroused considerable interest . Copolymers containing pH-responsive ionizable groups, such as carboxylic acids and amines, have been extensively investigated.…”

“…Among them, fluorescent copolymers have attracted significant attention due to their high stability, signal amplification, designable structure, and high water solubility. 13 Stimuli-responsive copolymers that can respond to external stimuli or changes in the surrounding environment, 14,15 for example, pH, 16,17 temperature, 18,19 light, 20−22 magnetism, 23 and other types, to make adaptable changes have aroused considerable interest. 24 Copolymers containing pH-responsive ionizable groups, 25 such as carboxylic acids and amines, have been extensively investigated.…”

Transient absorption spectroscopy

“…DBD dyes can, for example, be synthesized in such a way that they are integrated at different positions into biomolecules like lipids, which can then be used to investigate membrane structures using fluorescence microscopy [14]. Dyes are also valuable as pH [54], temperature, or oxygen sensors [55], where lifetime or spectral changes can be used to observe changes in the sample matrix for industrial or medical parameter observations.…”