A family of N-crowned 4-
p-(aminophenyl)-2,6-diphenylpyridines
DA (
1-
6) has been synthezised, characterized,and studied as potential hosts for the signaling of cationic and anionic guests. The ditopic probes contain twocoordination sites, a monodentate 2,6-diphenylpyridine and an anilino group with macrocycles of different ring size,denticity, and type of secondary heteroatom (O and/or S). X-ray structure analysis of aza-oxa-thia-crowned
5indicated a largely planar chromophore. Optical spectroscopic and electrochemical studies revealed that the anilino-type donor (
D) and the 2,6-diphenylpyridine acceptor (
A) are strongly
-conjugated, entailing intense intramolecularcharge-transfer absorption bands at 340 nm. Binding studies with protons and metal ions (
M = Cu
2+, Zn
2+, Hg
2+,Fe
3+, Pb
2+, Ni
2+, Cd
2+) showed shifts of the band to the visible (440 nm) when coordination at the pyridine groupoccurs, strengthening its acceptor character. In contrast, no band in the visible is formed if binding takes place atthe anilino group. Three different responses were found for various pairs of
DA and
M: selective metal coordinationto
D or
A as well as coordination at both sites. A selective response was found for
5 and Hg
2+. Because of themultitude of coordination-induced effects, the
DA-
M ensembles were further employed for differential anion sensing.In this protocol, the addition of an anion
X to a certain, weakly coordinated
DA-
M can (i) lead to the formation ofa ternary ion pair complex (
DA-
M-
X), (ii) change the preference for
A or
D coordination, (iii) induce dissociationof the complex, or (iv) can have no effect. Various patterns of absorption changes were obtained as a result ofdifferent responses (i)-(iv) of the
DA-
M's in the presence of various
X's. Data analysis yielded recognition patternsfor acetate, F
- and CN
-, demonstrating the potential of simple chromogenic host-guest pairs for differential anionsignaling.