FLUORESCENCE OF SILYL AND GERMYL KETONES AND THEIR PRIMARY PHOTOCHEMICAL PROCESSES

Dual fluorescence was observed for several mono- and bis-silyl and -germyl ketones in solution at room temperature. From their fluorescence spectra, excitation spectra, quantum yields, and time profiles, the observed fluorescence was assigned to the S2 (the second lowest excited singlet state) --> S0 (the ground state) one and the S1 (the lowest excited singlet state) --> S0 one. For the employed mono-M ketones (Ph(n)Me3-nMCOPh, M = Si or Ge), their S2 lifetimes in cyclohexane were shorter than 160 ps and their S1 ones lay between 0.8 and 2.5 ns. For bis(triphenylsilyl) ketone in cyclohexane, its S2 lifetime was 160 ps and its S1 one as long as 460 ns. Norrish type I cleavage of these ketones in solution was also studied with time-resolved optical absorption and ESR techniques.