Modulating the Photochemistry of Bipyridylic Compounds by Symmetric Substitutions

A quantum electronic study of the effect of substituents on (2,2'-bipyridyl)-3,3'-diol and (2,2'-bipyridyl)-3,3'-diamine is presented. A large difference in the photochemical behavior between the original and the substituted selected systems is expected. For the sake of simplicity, the study is restricted to the symmetrically bi-substituted compounds: fluorine, the more electronegative atom and thus a strong σ-acceptor but also a weak π-donor group, and NO2, a strong π-acceptor substituent. Among the large set of compounds studied, two receive special attention: 5,5'-dinitro-(2,2'-bipyridyl)-3,3'-diamine and 6,6'-difluoro-(2,2'-bipyridyl)-3,3'-diol. While in the former case the nitro substitution transforms (2,2'-bipyridyl)-3,3'-diamine, previously suggested to behave as a photomemory material, into a simple fluorescent species, the latter substitution turns (2,2'-bipyridyl)-3,3'-diol into a fresh new candidate for a photomemory device.Modulating photochemistry though substituent effects: Symmetric bisubstitutions on bipyridylic compounds modify the photochemistry by either enhancing or decreasing the probability to obtain a stable photochromic tautomer that can revert to the original form upon irradiation of different wavelength (see scheme). © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.