Hypsochromic shift

Abstract: To develop a zinc(II)-selective emission ratiometric probe suitable for biological applications, we explored the cation-induced inhibition of excited-state intramolecular proton transfer (ESIPT) with a series of 2-(2'-benzenesulfonamidophenyl)benzimidazole derivatives. In the absence of Zn(II) at neutral pH, the fluorophores undergo ESIPT to yield a highly Stokes' shifted emission from the proton-transfer tautomer. Coordination of Zn(II) inhibits the ESIPT process and yields a significant hypsochromic shift of the fluorescence emission maximum. Whereas the paramagnetic metal cations Cu(II), Fe(II), Ni(II), Co(II), and Mn(II) result in fluorescence quenching, the emission response is not altered by millimolar concentrations of Ca(II) or Mg(II), rendering the sensors selective for Zn(II) among all biologically important metal cations. Due to the modular architecture of the fluorophore, the Zn(II) binding affinity can be readily tuned by implementing simple structural modifications. The synthesized probes are suitable to gauge free Zn(II) concentrations in the micromolar to picomolar range under physiological conditions.

Abstract: Three different cruciforms containing the 1,4-bis-4'-pyridylethynyl-2,5-distyrylbenzene or the 1,4-bis-phenylethynyl-2,5-distyrylbenzene unit were synthesized and investigated with respect to their metal sensing properties. Upon addition of metal cations to these cruciforms, either a bathochromic or hypsochromic shift in emission and absorption is observed. The shift depends on whether the metal coordinates preferentially to the pyridine or to the dibutylaniline branches of the cruciforms. The three cruciforms were exposed to a selection of metal cations in dichloromethane, and their emission was examined. The cruciforms show differential sensing of metal cations, that is, different metals can be specifically discerned upon exposure to three cruciforms but not when exposed to only one. The system can discern calcium from magnesium cations and silver from mercury or lithium cations.

Abstract: Establishing a simple and versatile design strategy to finely modulate emission colors while retaining high luminescence efficiency and color purity remains an appealing yet challenging task for the development of multi-resonance-induced thermally activated delayed fluorescence (MR-TADF) materials. Herein, we demonstrate that the strategic introduction of electron-withdrawing imine and electron-donating amine moieties into a versatile boron-embedded 1,3-bis(carbazol-9-yl)benzene skeleton enables systematic hypsochromic and bathochromic shifts of narrowband emissions, respectively. By this method, effective electroluminescence color tuning was accomplished over a wide visible range from deep-blue to yellow (461-571 nm), using the same MR molecular system, without compromising very narrow spectral features. Deep-blue to yellow organic light-emitting diodes with maximum external quantum efficiencies as high as 19.0-29.2 % and superb color purity could be produced with this family of color-tunable MR-TADF emitters.