Dithieno[3,2-a:2′,3′-c]phenazine-based chemical probe for anions: a spectroscopic study of binding

Abstract

The synthesis of a new anion-responsive molecule N,N′-(2,5-bis(4-(tert-butyl)phenyl)dithieno[3,2-a:2′,3′-c]phenazine-9,10-diyl)bis(4-methylbenzenesulfonamide) (1) is reported. The sensitivities of the spectroscopic properties of 1 in the presence of various anions were examined using UV-vis absorption spectroscopy, fluorescence and ¹H NMR titration experiments. Strong binding of 1 to carboxylate, cyanide, fluoride and dihydrogen phosphate anions results in an increase in quantum yield for emission of 1, and changes in its ¹H NMR chemical shifts. A significant electrostatic interaction of the tetrabutylammonium cation with 1, upon strong binding with the counter anion, was also indicated by the chemical shifts observed in the ¹H NMR titrations. Binding constants of 1 to anions are also calculated based on the binding isotherms derived from NMR and UV-vis titrations. DFT calculations show that the anion does not significantly impact the HOMO/LUMO levels (and subsequently the S₀ → S₁ transition), but rather changes the strength of the S₀ → S₂ transition, which accounts for the observed changes in the UV-vis spectra.