Synthesis, photophysics and theoretical ab initio calculations of a bizwitterionic compound modeling the phototautomer of bipyridyl-diol

A new compound, 3-hydroxy-1,1′-dimethyl-3-oxido-[2,2′-bipyridinedium]hydroxide hydrate (1,1′-dimethyl-3,3′-dioxido[2,2′-bipyridinedium] - DDB), was synthesized as a model of the transient product of the excited state intramolecular proton transfer (ESIPT) reaction (excited phototautomer) of bipyridyl-diol (BP(OH)2). The photophysics and quantum chemical ab initio calculations of DDB are reported. The results confirm the zwitterionic character of the excited phototautomer of BP(OH)2.