Flavanone and its ortho-hydroxychalcone isomer can be interconverted by changes in pH, making an attractive molecular switch scaffold. The ortho-hydroxychalcone, being an extended aromatic system, can also be utilized as a fluorophore with metal binding capacity. The scaffold can also be dramatically changed from previous studies by exchanging the acetophenone and benzaldehyde derived rings for hetero and extended aromatic rings to determine their effect on the midpoint pH. A variety of methoxy-/fluoro-substituted and hetero-/extended aromatic chalcones were screened in methanol and pH 13.50 buffer to determine if the scaffolds were fluorescent. From a possible 32 chalcones in the two conditions, 18 neutral and 16 anionic species had observable fluorescence (signal \u3e 19,000). The scaffold, regardless of charge, had very large Stokes shifts often exceeding 100 nm. Several interesting substitution patterns emerged where 5\u27-substitution of the scaffold seemed to enhance fluorescent signal. The two brightest fluorophores 5\u27,4- and 5\u27,3-dimethoxychalcones, both in methanol, were both substituted at this position. The 4-substitution also showed enhanced fluorescence in pH 13.50 buffer, making it an intriguing high pH sensing fluorophore. Up to this point, the phenyl rings of the ortho-hydroxychalcone flavanone (OHC-Fla) switch were thought to be essential to the equilibrium of the switch. It was shown that replacing these moieties did not affect the viability of the switch and as a result of these studies the lowest and highest midpoint pH values to date were achieved. The switch has shown itself to be robust, reliable, and predictable in spite of large structural modifications
