TY  - JOUR
A1  - Schwarze, Thomas
T1  - Determination of Pd2+ by fluorescence enhancement caused by an off-switching of an energy- and an electron transfer
JF  - ChemistrySelect
N2  - In this paper, we introduce a fluorescent dye 1, which is able to detect selectively Pd2+ by a clear fluorescence enhancement (FE) in THF. In the presence of eight Pd2+ equivalents, we observed a fluorescence enhancement factor (FEF) of 28.3. The high Pd2+ induced FEF can be explained by an off switching of multiple quenching processes within 1 by Pd2+. In the free dye 1 a photoinduced electron transfer (PET) and energy transfer (ET) takes place and quenches the anthracenic fluorescence. The coordination of eight Pd2+ units by the alkylthio-substituted porphyrazine receptor suppresses the PET and ET quenching process and the anthracenic fluorescence is switched on.
KW  - Palladium ion
KW  - electron transfer
KW  - energy transfer
KW  - fluorescence
KW  - porphyrazine
Y1  - 2021
U6  - https://doi.org/10.1002/slct.202003975
SN  - 2365-6549
VL  - 6
IS  - 3
SP  - 318
EP  - 322
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Schwarze, Thomas
A1  - Kelling, Alexandra
A1  - Sperlich, Eric
A1  - Holdt, Hans-Jürgen
T1  - Influence of regioisomerism in 9-anthracenyl-substituted dithiodicyanoethene derivatives on photoinduced electron transfer controlled by intramolecular charge transfer
JF  - ChemPhotoChem
N2  - In this paper, we report on the fluorescence behaviour of three regioisomers which consist of two 9-anthracenyl fluorophores and of differently substituted dithiodicyanoethene moieties. These isomeric fluorescent probes show different quantum yields (phi(f)). In these probes, an oxidative photoinduced electron transfer (PET) from the excited 9-anthracenyl fluorophore to the dithiodicyanoethene unit quenches the fluorescence. This quenching process is accelerated by an intramolecular charge transfer (ICT) of the push-pull pi-electron system of the dithiodicyanoethene group. The acceleration of the PET depends on the strength of the ICT unit. The higher the dipole moment of the ICT unit, the stronger the observed fluorescence quenching. To the best of our knowledge, this is the first report of a regioisomeric influence on an oxidative PET by an ICT.
KW  - anthracene
KW  - charge transfer
KW  - electron transfer
KW  - fluorescence
KW  - isomerism
Y1  - 2021
U6  - https://doi.org/10.1002/cptc.202100070
SN  - 2367-0932
VL  - 5
IS  - 10
SP  - 911
EP  - 914
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Schwarze, Thomas
A1  - Mertens, Monique
A1  - Mueller, Peter
A1  - Riemer, Janine
A1  - Wessig, Pablo
A1  - Holdt, Hans-Jürgen
T1  - Highly K+-Selective Fluorescent Probes for Lifetime Sensing of K+ in Living Cells
JF  - Chemistry - a European journal
N2  - The new K+-selective fluorescent probes 1 and 2 were obtained by Cu-I-catalyzed 1,3-dipolar azide alkyne cycloaddition (CuAAC) reactions of an alkyne-substituted [1,3]dioxolo[4,5-f][1,3]benzodioxole (DBD) ester fluorophore with azido-functionalized N-phenylaza-18-crown-6 ether and N-(o-isopropoxy) phenylaza-18-crown-6 ether, respectively. Probes 1 and 2 allow the detection of K+ in the presence of Na+ in water by fluorescence enhancement (2.2 for 1 at 2000mm K+ and 2.5 for 2 at 160mm K+). Fluorescence lifetime measurements in the absence and presence of K+ revealed bi-exponential decay kinetics with similar lifetimes, however with different proportions changing the averaged fluorescence decay times ((f(av))). For 1 a decrease of (f(av)) from 12.4 to 9.3ns and for 2 an increase from 17.8 to 21.8ns was observed. Variation of the substituent in ortho position of the aniline unit of the N-phenylaza-18-crown-6 host permits the modulation of the K-d value for a certain K+ concentration. For example, substitution of H in 1 by the isopropoxy group (2) decreased the K-d value from >300mm to 10mm. 2 was chosen for studying the efflux of K+ from human red blood cells (RBC). Upon addition of the Ca2+ ionophor ionomycin to a RBC suspension in a buffer containing Ca2+, the fluorescence of 2 slightly rose within 10min, however, after 120min a significant increase was observed.
KW  - electron transfer
KW  - fluorescence lifetime
KW  - fluorescent probes
KW  - living cells
KW  - potassium
Y1  - 2017
U6  - https://doi.org/10.1002/chem.201704368
SN  - 0947-6539
SN  - 1521-3765
VL  - 23
SP  - 17186
EP  - 17190
PB  - Wiley-VCH
CY  - Weinheim
ER  -