CT-operated bifunctional fluorescent probe based on a pretwisted donor-donor-biphenyl

Taking into account the structural requirements for TICT-type sensor molecules, a general synthetic route to derive pH and cation-responsive pretwisted donor (D)-donor (D) biphenyls (b) equipped with donor receptors is developed and a first model compound containing a mono aza-15-crown-5 and a DMA receptor is synthesized, see Scheme 1. The spectroscopic properties of this new bifunctional D-D biphenyl are studied in the non-polar and polar solvents cyclohexane, acetonitrile, and methanol. Protonation as well as complexation studies are performed with the representative metal ions Na(I), K(I), Ca(II), Ag(I), Zn(II), Cd(II), Hg(II), and Pb(II) to reveal the potential of this molecule for communication of whether none, only one, or both binding sites are engaged in analyte coordination by spectroscopically distinguishable outputs. The results are compared to those obtained with closely related donor (D)-acceptor (A) substituted biphenyl-type sensor molecules and are discussed within the framework of neutral and ionic D-A biphenyls.