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.

No abstract

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.

We report on the reversible fluorescence switching of biodegradable nanoparticles of spiropyranterminated poly(ε-caprolactone) (SP-PCL) for superresolution fluorescence imaging. SP-PCL was synthesized via ring-opening polymerization using hydroxyl-containing SP derivative as the initiator. SP-PCL solution in THF or dioxane exhibits fast photochromism from colorless to blue upon UV irradiation due to the transformation of SPs in SP-PCL into merocyanines (MCs). Although both SP-PCL solution and MC-PCL solution do not fluoresce, SP-PCL nanoparticle dispersion fabricated via nanoprecipitation in aqueous media, in which SP molecules were embedded into the hydrophobic PCL matrix, displays considerable green emission at 530 nm at an excitation wavelength of 420 nm. Upon <420 nm irradiation, the resulting MC-PCL nanoparticles show strong red emission at 650 nm when excited at 420 nm. SP-PCL nanoparticles display green−red dual-color intrinsic fluorescence switching upon alternated UV/vis illumination. Green emission from SP in SP-PCL nanoparticles is observed before UV irradiation while red emission from MCs in MC-PCL nanoparticles after UV irradiation. For both SP-PCL and MC-PCL nanoparticles, the critical excitation wavelength is determined at 420 nm, at which the photoinduced interconversion of MC-and SP-forms are found to be at equilibrium. Positive and inverse photoisomerizations monitored using time-dependent fluorescence spectra show that blue light excitation above 420 nm yields green emission of SPs in SP-PCL nanoparticles while light irradiation below 420 nm imparts photoisomerization (SP to MC) and thus red emission of MCs in MC-PCL nanoparticles. Green and red fluorescence can be optically switched and imaged under fluorescent microscopy. Biodegradable SP-PCL nanoparticles are demonstrated to be promising photoswitchable fluorophores for localization-based super-resolution microscopy, evidencing by resolving nanostructures with sub-50 nm resolution in poly(vinyl alcohol) (PVA) film and live cells.

The parameter value chosen to measure driving performance affects the accuracy of the estimated fatigue level. Methods to analyze the sensitivity of these parameter values were proposed. Standard deviation of lane position (SDLP) and steering reversal rate (SRR) were considered to assess fatigue, and the sensitivity of these parameters was analyzed from the time domain and value domain. Thirty-six male drivers participated in a field test. Lane position, steering wheel angle data, and self-reported fatigue level (scored on the Karolinska sleepiness scale) were recorded. SDLP results indicate that the maximum average coefficient with fatigue level reached .11, with a unified statistical interval of 202 s when the consecutive analysis method was used; the maximum average coefficient was .12 with a unified interval of 120 s when the maximum analysis method was used. SRR results indicate that a steering angle difference of 6° was the most sensitive threshold for driver fatigue level and has an average correlation coefficient of .42, which demonstrated that SRR was more reliable than SDLP for monitoring fatigue level. With the use of the optimal parameter value, the variation results of SDLP and SRR at each fatigue level were examined, and results indicate that driving ability was impaired as fatigue level increased. The methods and results can be applied to analyses of fatigued or drowsy driving.

HIGHLIGHTS• High performance Al nanostructures/ZnO quantum dots heterostructure photodetectors with a controllable geometry of the Al nanostructures are demonstrated.• Light utilization of the photoactive layers is significantly boosted with the Al nanostructures.• The light confinement effect is inherently determined by the geometries of the Al nanostructures.

No abstract