We compare the kinetics of intersystem crossing at room temperature in different solvents for a family of aromatic ketones: benzophenone, anthrone, xanthone, and para-substituted benzophenones. We report our recent observations: (1) fast buildup (kf1 < 10 ps) of anthrone transient absorption in dioxane followed by a long {k2l ~175 ps) decay; (2) fast buildup {hr1 < 10 ps) of anthrone transient absorption in benzene; (3) fast buildup {k~l = 8 ± 2 ps) of benzophenone transient absorption in ethanol; (4) fast buildup (fe™1 = 6.5 ± 2 ps) of 4,4'-dimethoxybenzophenone transient absorption in benzene. We conclude that the rates of intersystem crossing for this family of aromatic ketones are all approximately the same.

Excited state absorption spectra of quinoxaline in benzene, isooctane, and cis-1,3-pentadiene at 7 and 130 ps after excitation are reported. Picosecond absorption kinetics at 422 and 533 nm are also reported. In the nonaromatic solvents, bands at ∼425 nm (Sn←S1 and Tn←T1) and ∼ 530 nm (mostly Sn←S1) are observed in the transient spectra. Decay of the ∼530-nm band gives k−1isc?23 ps in the nonaromatic solvents. In benzene solvent, the excited state spectra are more complex, the decay kinetics are longer, and quinoxaline–benzene exciplex formation is suggested.

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