Dynamic proton-induced two-stage emission switching in donor-functionalized bis(dehydrobenzo[n]annuleno)benzenes and 1,2,4,5-tetrakis(phenylethynyl)benzene

Titration of three electron donor-functionalized bis(dehydrobenzo[n]annuleno)benzenes and a corresponding acyclic 1,2,4,5-tetrakis(phenylethynyl)benzene derivative with trifluoroacetic acid in CH2Cl2 resulted in two-stage emission switching behavior in which initial acidification caused bathochromic shifts, followed by dramatic hypsochromic shifts upon further addition of acid. Differences in the various spectra are rationalized by structure and chromophore architecture. The results indicate independent manipulation of frontier molecular orbital energy levels by stepwise ion addition, therefore suggesting transient and tunable intramolecular charge transfer systems upon partial protonation.