Selective lithium complexation by photoactive aza-cages bearing the anthracene function

Three aza-cages with the anthracene-containing photoactive groups L1, L2, a nd L3 have been synthesized. All compounds are able to selectively encapsul ate a lithium ion and solid complexes have been isolated. The formation equ ilibria have been investigated by UV/Vis and H-1, C-13 and Li-7 NMR spectro scopic techniques. The fluorescence emission of both free ligands and lithi um complexes have been investigated. Results indicate that the CHEF (chelat ion enhancement of the fluorescence) effect obtained by Lithium coordinatio n exits although lower than that occurring upon full protonation.