3D optical data storage based on two-photon processes provides a mechanism for writing and reading data with less crosstalk between multiple memory layers, due to the quadratic dependence of two-photon absorption (2PA) on the incident-light intensity.[1] This capacity for highly confined excitation and intrinsic 3D resolution affords immense information storage capacity (up to 10 12 bits cm -3). [2] Recently, the use of photochromic materials for 3D memory has received intensive interest because of several major advantages over current optical systems, including their erasable/rewritable capability, high resolution, and high sensitivity. [3] Among the several classes of photochromic materials, diarylethenes with heterocyclic aryl groups are the most promising candidates for applications because of their excellent fatigue resistance, picoseconds switching time, high photoisomerization quantum yields, and absence of thermal isomerization. [4,5] Various optical systems for reading and writing 3D memories using diarylethene derivatives as storage media have been reported, [3] where several methods using fluorescence readout were used to avoid destructive readout. [4] In particular, Jares-Erijman and Irie used Lucifer Yellow I as the donor and bis(thienyl)ethane as the acceptor to build fluorescent molecules and they developed a general conceptual reading/writing system based on fluorescence resonance energy transfer (FRET), where they found that the single-photon fluorescence emission of the donor is reversibly modulated by cyclical transformations of the photochromic acceptor upon irradiation with appropriate UV and visible light. [5,6] This system provided a novel method of using fluorescence to readout the recorded data without simultaneously erasing part of the stored information. However, to the best of our knowledge, modulation of the twophoton fluorescence emission of a dye by a photochromic diarylethene has not been reported as the readout method in a 3D optical-data-storage system. This may be due, in part, to the difficulty in making suitable materials with large 2PA cross sections, high fluorescence quantum yields, and high photostability, in which the emission spectrum properly overlaps the absorption spectrum of one of the isomers of the photochromic diarylethene. In this paper, we demonstrate a novel two-photon 3D optical-storage system based on the modulation of the fluorescence emission of a highly efficient two-photon absorbing fluorescent dye and a photochromic diarylethene. This system is suitable for recording data in thick storage media and providing a non-destructive readout method without exhibiting any apparent fatigue, even after 10 000 readout cycles. The storage medium consists of a commercial available photochromic molecule (diarylethene 1), 1,2-bis(2-methylbenzo[b]thiophen-3-yl)hexafluorocyclopentene, and a specially designed two-photon absorbing dye (2,7-bis[4-(9,9-didecylfluoren-2-yl)vinyl]phenylbenzothiazole (fluorene derivative 2) (Scheme 1). Figure 1 shows the absorption spectra of t...

We report the synthesis of a dithienylethene-tetraphenylethene (DTE-TPE) conjugated photochromic fluorophore which simultaneously exhibits aggregation-induced emission and reversible fluorescence switching. Photochromic DTE-TPE turns cyan-blue after 5 s of UV irradiation and exhibits a strong green emission at 520-540 nm upon excitation with visible light when present in nanoparticles and the solid state, in contrast to non-fluorescence in solution. DTE-TPE exhibits reversible fluorescence switching under alternating irradiation with UV and visible light (wavelengths greater than 440 nm), when present in nanoparticles and the solid state. The continuous readout of the emissive DTE-TPE film over 1 h upon 440 nm excitation-irradiation causes only a 7% reduction in emission intensity for DTE-TPE. The superresolution fluorescence nanolocalization indicates that the vicinal DTE-TPE emitters show sub-100 nm resolution which is higher than for conventional fluorescent imaging. The spectroscopic and imaging data provides initial guidelines for the screening of molecular scale memory units with the corresponding excitation and detection wavelengths for signal readout and super-resolution imaging agents.

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A new strategy for narrowing the size distribution of colloidal quantum dots (QDs) was developed by combining cation exchange and quantized Ostwald ripening. Medium-sized reactant CdS(e) QDs were subjected to cation exchange to form the target PbS(e) QDs, and then small reactant CdS(e) QDs were added which were converted to small PbS(e) dots via cation exchange. The small-sized ensemble of PbS(e) QDs dissolved completely rapidly and released a large amount of monomers, promoting the growth and size-focusing of the medium-sized ensemble of PbS(e) QDs. The addition of small reactant QDs can be repeated to continuously reduce the size distribution. The new method was applied to synthesize PbSe and PbS QDs with extremely narrow size distributions and as a bonus they have hybrid surface passivation. The size distribution of prepared PbSe and PbS QDs are as low as 3.6% and 4.3%, respectively, leading to hexagonal close packing in monolayer and highly ordered three-dimensional superlattice.