= Solution
<DBU> removes the proton from 1, restoring its zinc-binding ability. <zinc> returns from 2 to 1; the regenerated free 2 captures <lithium> from 3, restoring the preferred initial sorting. Thus \b[the reporter returns predominantly to 554 nm], while <DBU> becomes its <conjugate acid> and trifluoroacetate remains as counterion. This assumes the added base is strong enough under the solvent conditions and does not itself compete effectively for either metal. Reversing a <fluorescence> shift without checking speciation would not establish all these transfers on its own.
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