We report the rational design of the matrix-free carbon dots (C-dots) with long wavelength and wavelengthtunable room-temperature phosphorescence (RTP). Taking advantage of microwave-assisted heating treatment, three RTP C-dots in boric acid (BA) composites are synthesized by using diethylenetriaminepentakis (methylphosphonic acid) as a multiple-sites crosslink agent, a moderately acid catalyst and P source; phenylenediamines (either o-PD, m-PD, or p-PD, respectively) as building block while BA as a carbon-ization-retardant matrix. After the water-soluble BA matrix is removed by dialysis, three matrix-free C-dots are obtained with RTP emission at 540, 550 and 570 nm under an excitation wavelength of 365 nm. Alterations of RTP emission of three matrix-free C-dots are ascribed to the difference in their particle size and band gap from n-π* transition. Furthermore, the application of three matrix-free C-dots are successfully performed in information encryption and decryption.

The understanding of the dissolution processes of solids is important for the design and synthesis of solids in a controlled and precise manner and for predicting their fate in the aquatic environment. We report herein single-particle-based confocal laser scanning microscopy (CLSM) for tracking the dissolution surface kinetics of a single fluorescent cyclodextrin metal−organic framework (CD-MOF). As a proof of concept, CD-MOF containing fluorescein, named as CD-MOF⊃FL, was synthesized by encapsulating fluorescein into the interior of CD-MOF via a vapor diffusion method and used as a single-particle dissolution model because of its high FL efficiency and unique structure. The morphology of CD-MOF⊃FL and the distribution of fluorescein within CD-MOF⊃FL were characterized. The growth and dissolution processes of CD-MOF⊃FL at the single-particle level were visualized and quantified for the first time by recording the change of the fluorescence emission. Three processes, including nucleation, germination growth, and saturation stage, were found in the growth of CD-MOF⊃FL, and the growth kinetics followed Avrami's model. The dissolution rate at the face of a single CD-MOF⊃FL crystal was slower than that of its arris, and the dissolution rate of the CD-MOF⊃FL crystal was increased with the increase of the water amount in methanol solution. The dissolution process of the CD-MOF⊃FL crystal was a competitive process of erosion and diffusion in different methanol aqueous solutions, and the dissolution kinetics followed the Korsmeyer−Peppas model. These results offer new insights into the nature of dissolution kinetics of CD-MOF⊃FL and provide new venues for the quantitative analysis of solid dissolution and growth at the single-particle level.