Novel EDTA-Ligands Containing an Integral Perylene Bisimide (PBI) Core as Optical Reporter Unit

TL;DR

This paper reports the synthesis and characterization of novel water-soluble EDTA-based perylene bisimide ligands that act as optical sensors, capable of metal ion detection through fluorescence changes and aggregation behavior.

Contribution

It introduces new EDTA-ligand PBIs with integrated PBI cores, demonstrating their metal complexation and potential as optical sensors with unique aggregation-dependent fluorescence responses.

Findings

Efficient coordination of trivalent metal cations in water and DMSO.

Metal ions induce formation of fluorescent supramolecular aggregates in water.

Complexation suppresses PET, resulting in fluorescence enhancement.

Abstract

The synthesis, characterization and metal complexation of a new class of perylene bisimides (PBIs) being an integral part of ethylenediaminetetraacetic acid (EDTA) is reported. The simplest representative, namely derivative 1a, was synthesized both by a convergent as well as a direct approach while the elongated derivatives, 1b and 1c, were obtained only via a convergent synthetic pathway. All these new prototypes of water-soluble perylenes are bolaamphiphiles and were fully characterized by 1H- and 13C-NMR spectroscopy, matrix assisted laser desorption ionization, time of flight (MALDI-TOF) mass spectrometry and IR spectroscopy. In order to acquaint for the behaviour in solution of our PBIs bearing dentritic wedges, the simplest derivative, 1a, was chosen and tested by means of UV/Vis and fluorescence spectroscopy as well as by zeta-potential measurements. A photoexcitation induced intramolecular photo-electron transfer (PET) can be observed in these molecules. Therefore potential applications as sensor can be imagined. Model compound 1a efficiently coordinates trivalent metal cations both in water and in dimethyl sulfoxide (DMSO). Significantly, the effects of the complexation strongly depend on the aggregation state of the PBI molecules in solution. As a matter of fact, in water, the presence of M3+ ions triggers the formation of light emitting supramolecular aggregates (excimers). On the other hand, in DMSO-rich solutions metal complexation leads to the suppression of the PET and leads to a strong fluorescence enhancement.