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A new facile method that employs high‐power sonication is used to break up firmly agglutinated nanodiamonds and obtain dispersion just as effectively as stirred‐media milling. The dispersion properties of the de‐agglutinated nanodiamonds in various nonaqueous solvents, and the pH‐dependent dispersion/precipitation behavior of the hydrosols are presented (see figure). The brownish color of the colloids is attributed mostly to the Rayleigh scattering superimposed over the finite absorption in the visible wavelength.

Femtosecond time-resolved fluorescence up-conversion spectroscopy has been used in a study of the photoinduced isomerization reactions of a rotation-restricted trans-azobenzene (trans-AB) derivative capped by a crown ether (1), a chemically similar open derivative (2), and unsubstituted trans-AB (3) after excitation to the S 1 (np*) state at l ¼ 475 nm in dioxane solution. The observed biexponential temporal fluorescence profiles for 1 and 2 were almost indistinguishable within experimental error. The fitted fast fluorescence decay times (AE2s) for the two compounds were t 1 (1) ¼ (0.79 AE 0.20) and t 1 (2) ¼ (1.05 AE 0.20) ps, compared to t 1 (3) ¼ (0.37 AE 0.06) ps. The second decay components could be described with t 2 (1) ¼ (20.3 AE 9.5) resp. t 2 (2) ¼ (19.0 AE 6.0) ps, vs. t 2 (3) ¼ (3.26 AE 0.85) ps. The very similar lifetimes strongly suggest that trans-cis isomerization of 1 and 2 after S 1 excitation is governed by the same mechanism. Since 1 cannot isomerize by a simple large-amplitude rotation of one of the phenyl rings about the central NN bond, the isomerization dynamics of both ABs should be better described as ''inversion'' at the N atom(s) rather than large-amplitude ''rotation''.