Selective and pH-Independent Detection of Ba2+ in Water by a Benzo-21-crown-7-Functionalized BODIPY

Herein, we report on highly Ba2+ selective fluorescence sensing in water by a fluorescent probe consisting of a benzo-21-crown-7 as a Ba2+ binding unit (ionophore) and a tetramethylated BODIPY fluorophore as a fluorescence reporter. This fluorescent probe showed a Ba2+ induced fluorescence enhancement (FE) by a factor of 12±1 independently of the pH value and a high Ba2+ sensitivity with a limit of detection (LOD) of (17.2±0.3) μM. Moreover, a second fluorescent probe consisting of the same BODIPY fluorophore, but a benzo-18-crown-6 as a cation-responsive binding moiety, showed an even higher FE upon Ba2+ complexation by a factor of 85±3 and a lower LOD of (13±3) μM albeit a lower Ba2+ selectivity. The fluorescence sensing mechanism of Ba2+ was further investigated by time-resolved fluorescence as well as transient absorption spectroscopy (TAS) and it turned out that within these probes a blocking of a photoinduced electron transfer (PET) by Ba2+ is very likely responsible for the FE.

Femtosecond excited state dynamics of a stilbene–viologen charge transfer complex assembled via host–guest interaction

The ultrafast photoinduced electron transfer in a supramolecular charge transfer complex was studied.

Observations on transition metal free biaryl coupling: potassium tert-butoxide alone promotes the reaction without diamine or phenanthroline catalysts

Biaryl coupling (often labelled 'C-H activation') of aromatic systems can be achieved by potassium tert-butoxide alone in the absence of any amine or bipyridine catalyst (1,10-phenanthroline or N,N'-dimethylethylenediamine being the most common), previously reported to be essential. Various mechanistic studies and observations are presented which suggest that when 1,10-phenanthroline is employed as the catalyst, the alkoxide is destroyed almost immediately.

Size-selective catalysis of ester and anilide cleavage by the dinuclear barium(II) complexes of cis- and trans-stilbenobis(18-crown-6)

The basic ethanolysis of esters and anilides endowed with a distal carboxylate anchoring group is catalyzed by the dinuclear Ba(II) complexes of cis- and trans-stilbenobis(18-crown-6). Comparison with the catalytic efficiency of a mononuclear model catalyst demonstrates that the two metal ions in the dinuclear complexes act synergically. The cis form of the catalyst is more efficient than the trans form and much more sensitive to the size of the substrate, showing that the concave shape imposed by the cis double bond is better suited for catalysis. An experiment in which the less active trans form is photoactivated in situ is also reported.