Compounds having two benzocrown ether units bridged by a mono-, di-, or trisilanylene
unit were prepared, and ionochromic effects on their optical properties were studied. Of
these, disilanylene- and trisilanylene-bridged ones exhibited clear ionochromism in the
emission spectra and the intensity of the original emission band at about 320 nm decreased
and a new broad band centered at 400 nm appeared when appropriate alkali or alkali-earth
metal ions were added into the acetonitrile solutions. In contrast, a monosilanylene-bridged
benzocrown ether and a disilanylbenzocrown ether showed ionochromic changes in different
fashions, indicating that the new emission band at low energy of the di- and trisilanylene-bridged benzocrown ethers in the presence of metal ions may be ascribed to the intramolecular π−π stacking. MO calculations were carried out to understand the ionochromism.