NEW PHOTOTAUTOMERIZING SYSTEMS - NONSYMMETRICAL DERIVATIVES OF [2,2'-BIPYRIDYL]-3,3'-DIOL

Six new phototautomerizing compounds, structural analogues of [2,2'-bi pyridyl]-3,3'-diol (BP(OH)(2)) and [2,2'-bipyridyl]3-ol, were synthesi zed. The electron-donating or electron-withdrawing substituent introdu ced next to the reactive proton transfer site (N atom) can modify the status of the internal hydrogen bonds, controlling the excited state i ntramolecular proton transfer mechanism in a predictable way. Ab initi o RHF/6-31 G* and semiempirical (PM3) calculations for the S-0 ground state were performed to determine the structural features that 'prepa re' the molecular system for its fate in the S-1 excited state. The ca lculated molecular geometries and Mulliken net charges were useful for interpreting photophysical data. The dramatic changes of phototautome ric fluorescence quantum yields are dependent on (1) molecular symmetr y lowering of the substituted BP(OH)(2) system and (2) electron densit y on the N atom(s). (C) 1998 Elsevier Science B.V. All rights reserved .