Spectroscopic and photophysical responses of a ruthenium(II) dication-calix[4]arenetetrasulfonate hybrid complex upon ion binding

A CS4-: (RuB32+)(2) hybrid complex as a new class of a chemosensor was prepared by an ion-exchange reaction, where CS4- and RuB32+ were calix[4]arenetetrasulfonate and a tris(2,2'-bipyridine)ruthenium(II) dication, respectively. In the solid state, one RuB32+ was shown to bury partly in the cavity of CS4- from the upper rim, while other RuB32+ sits near the CS4-:RuB32+ ion-pair to balance the total electric charge of the hybrid. In methanol, on the other hand, two RuB32+ molecules in the hybrid complex located in the vicinity of a CS4- molecule at analogous microenvironments as suggested by H-1-NMR. Spectroscopic and excited-state properties of RuB32+ in the hybrid were influenced by CS4- through the ion-excited dipole interaction and photoinduced electron transfer quenching. In the presence of a foreign cation as a guest, the emission intensity and lifetime of RuB32+ increased, demonstrating that CS4-: (RuB32+)(2) hybrid complex acted as a luminescent chemosensor. The mechanism of ion recognition was discussed in terms of changes in the photophysical properties of the hybrid complex. (C) 2002 Elsevier Science B.V. All rights reserved.