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A systematic structural investigation of R-phenyl-substituted 2,2':6',2"-terpyridines, a family of mono- and bifunctional charge transfer (CT)-operated fluorescent reporters for protons and metal ions, is presented. These molecules are equipped with non-binding and analyte coordinating donor substituents R (R = CF3, H, OMe, OH, DMA, A15C5 equaling monoaza-15-crown-5) of various donor strength and display CT-controlled spectroscopic properties and communication of analytereceptor interactions. The crystal structures of the neutral fluorescent probes are compared to the structures of their terpyridine-alkylated or -protonated counterparts that represent model systems for acceptor protonation or cation coordination. The aim is here a better understanding of the complexation-induced structural and spectroscopic changes and the identification of common packing motifs of bpb-R thereby taking into account the importance of terpyridine building blocks for the construction of supramolecular systems and coordination arrays revealing ππ interactions.
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
DD 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.