Synthesis and Optical Properties of 2,13-Dibenzothiazol-2'-yldibenzo[b,k]--18-crown-6. -Complexation of the new crown ether (I) with alkali-metal ions leads to an intramolecular charge transfer and causes changes of the fluorescence spectra. The intramolecular charge transfer takes place between the metal ions in the dibenzo-crown ether center moiety with the two benzothiazole groups. The potassium ion is able to form more stable complexes than the other alkali ions. Trifluoroacetic acid can cause an enhancement of the fluorescence properties owing to the effect of protonation. -