A rapid and mild esterification method using carboxylic 2,4,6-trichlorobenzoic anhydrides in the presence of 4-dimethylaminopyridine was developed. The method was also successfully applied to the synthesis of large-ring lactones, including Dl-2,4,6-tridemethyl-3-deoxymethynolide.

Fluorescence properties have been studied for Mn:ZnS crystallites with average diameter of 4 nm prepared by an aqueous colloidal method under 266 nm light excitation. The intensity ratio of the blue band at ∼430 nm to the orange band at ∼590 nm has decreased after the preparation on a time scale of hours in aqueous solution. On the other hand, hyperfine structures of Mn 2+ in the electron paramagnetic resonance spectrum have increased markedly on the same time scale in solution samples. These phenomena are attributed to the redistribution of defect centers in nanocrystals. Such phenomena have not been observed in samples incorporated into poly(vinyl alcohol). The orange emission is mainly due to the 6 A 1 r 4 T 1 transition of Mn 2+ , while the blue emission is tentatively assigned to the donor-acceptor pair transition in which the acceptor is related to the Zn 2+ vacancy. Fluorescence decay times of the blue and orange bands have been found to be ∼10 ns and ∼1 ms, respectively, the latter being the same as in the bulk samples. A weak fluorescent component with fast kinetics observed in the orange region has been identified as a tail of the blue band. No lifetime shortening of the Mn 2+ emission due to quantum confinement has been observed, contrary to reports in the literature.

We report observations of a new optical memory effect in Sm-doped ZnS nanocrystals and elucidate its mechanism. One of the salient properties of this effect is that the incident angle as well as the wavelength of incoming light is memorized with high resolution. We show that this effect is not based upon spectral selection of homogeneous absorption lines as in the persistent spectral hole-burning effect but upon recording of interference patterns of multiple-scattered light in disordered media. PACS numbers: 42.25.Hz, 42.25.Dd, 78.90. + t In strongly scattering media, various remarkable phenomena related to multiple scattering of light, such as coherent backscattering [1-3], memory effects [4], laser action without an external cavity [5], and Anderson localization of light [6], have been observed. To this list we add here a novel effect observed in Sm-doped ZnS nanocrystals, in which both the wavelength and the incident angle of incoming light is memorized with high resolution. Its appearance as the wavelength memory resembles that of the persistent spectral hole-burning effect [7]. However, we show that the mechanism is entirely different, and the effect is due to interference of multiple-scattered light in the medium. It is closely related to weak localization of light and expected to find application in high-density optical data storage.Sm-doped ZnS nanocrystals were prepared by the same procedure as that for CdS nanocrystals [8] with Zn-

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