Bipyridyl derivatives as photomemory devices: a comparative electronic-structure study.

The two isoelectronic bipyridyl derivatives [2,2'-bipyridyl]-3,3'-diamine (BP(NH(2))(2)) and [2,2'-bipyridyl]-3,3'-diol (BP(OH)(2)) are experimentally known to undergo very different excited-state double proton transfer processes that result in fluorescence quantum yields that differ by four orders of magnitude. Such differences have been theoretically explained in terms of topographical features in the potential energy surface and the likely presence of conical intersections. The hypothetical hybrid compound [2,2'-bipyridyl]-3-amin-3'-ol (BP(OH)(NH(2))) presents intermediate photochemical features of its "ancestors". In this report we analyze the photochemical properties of a whole family of "dark" (not fluorescent) states that can be accessed from each bipyridyl derivative upon irradiation of light of a given wavelength and their potential application as photomemory devices. In the light of our density functional theory (DFT), time-dependent DFT (TDDFT), and complete active space self-consistent field (CASSCF) calculations, BP(NH(2))(2) is the more likely candidate to become a photomemory device.