PHOTOPHYSICAL CHARACTERIZATION OF FLUORENONE DERIVATIVES

The photophysics of several fluorenone derivatives was studied using f luorescence and laser-induced optoacoustic spectroscopy. Electron-dona ting substituents increase the energy of the key upper triplet state ( T-3) which, for the parent compound, is responsible for the increased intersystem crossing quantum yield in non-polar solvents. Electron-wit hdrawing substituents decrease the energy of T-3, and an increase in t he intersystem crossing rate constant is observed. Halogen substitutio n leads to a heavy-atom effect, which is partially compensated by a de crease in the intersystem crossing rate constant due to changes in the energy gap between S-1 and T-3. For most compounds, an increase in th e internal conversion rate constant is observed. The magnitude of till s increase is a function of the nature of the substituent and its posi tion on the fluorenone ring. (C) 1997 Elsevier Science S.A.