We show that the organic salt 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) is a very interesting material for electro-optic applications in the near infrared. The electro-optic coefficients, namely r111, r221, r331, r113, r223, and r333, were determined in the spectral range of 700 up to 1535 nm using optical samples cut from large high quality bulk crystals. DAST combines large electro-optic coefficients, e.g., r111=77±8 pm/V at λ=800 nm and r111=47±8 pm/V at λ=1535 nm, with low dielectric constants, e.g., ε1=5.2±0.4. This combination leads to large polarization-optical coefficients.

Organic materials with large second-order nonlinear optical (NLO) susceptibilities are of interest because of their potential applications in optical signal processing and frequency conversion.['-31 Much work has therefore been devoted to the search for optimal molecular crystalline materials composed of stable chromophoric molecules with large molecular hyperpolarizabilities with an optimized orientation for large macroscopic NLO effects.Crystal growth research is of basic importance for the application of organic crystals in NLO and electro-optical devices.I4] Bulk crystalline samples of reasonable size and good quality are also essential for the accurate measurement of electro-optical and NLO coefficients in order to evaluate the potential for future applications. In addition, it has been found that, particularly in organic materials, the linear electro-optical responses are strongly dependent on the crystal quality.[" Furthermore, growth of bulk crystals of organic salts with large chromophoric cations has hardly been reported in the literature. In this work, we describe the growth of the organic salt crystal 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST), and the main results of the linear, nonlinear, and electro-optical characterization.In this crystal, the stilbazolium, one of the most efficient NLO chromophores, is the nonlinear optically active part.[61 The anion (tosylate) induces the non-centrosymmetric macroscopic crystal packing (see Fig. 2, bottom). DAST crystals have already been reported to have very large nonlinear optical su~ceptibilities.[~-~~~ The lack of reasonably large and optically homogeneous DAST crystals has hindered the accurate linear, nonlinear, and electro-optical characterization in earlier investigations of DAST.[*-'O1 DAST was synthesized by the condensation of 4-methyl-N-methyl pyridinium tosylate, which was prepared from 4-picoline and methyl toluenesulphonate, and 4-N,N-dimethylamino-benzaldehyde in the presence of pipendine (Scheme 1).DAST was then purified ( > 99.8 %) by recrystallization from water and methanol. Orange co-crystals, DAST . H20, in space group Pi (point group i, z = 2)[l2]were obtained from water or a methanol-water mixture. DAST can hardly be dissolved in non-polar and most polar solvents. Alcohol, however, is a reasonably good solvent for DAST and we found that methanol was the most suitable solvent for the growth of high-quality DAST crystals. The solubility curve for DAST in a methanol solution (see Fig. 1) was defined by saturating solutions at a high temperature and slowly cooling the solution in the presence of a precipitated solid to maintain equilibrium and analyzing the solution at defined temperatures.DAST single crystals were grown from a seeded saturated methanol solution (between 40 and 50°C with concentrations of about 4-5.5 g(DAST)/IOO g(so1vent)) by a 8 . 0 ) . I . , . , . , . , . , .

A fluoro-substituted cyanine showing reliable in vivo labelling of Aβ oligomers and potent neuroprotective effect against Aβ-induced toxicities is reported as a novel theranostic agent for the early diagnosis and therapy of Alzheimer's disease.

A novel series of monodisperse bis-dipolar emissive oligoarylfluorenes, OF(2)Ar-NPh, bearing an electron affinitive core, 9,9-dibutylfluorene as conjugated bridges, and diphenylamino as end-caps was successfully synthesized by a convergent approach using palladium catalyzed Suzuki cross-coupling. The results of optical and electrochemical investigations showed that the HOMO, LUMO, and energy gap of these diphenylamino endcapped oligoarylfluorenes can easily be modified or tuned by the use of various electron affinitive central aryl cores that included dibenzothiophene, phenylene, oligothiophenes, 2,1,3-benzothiadiazole, 4,7-dithien-2-yl-2,1,3-benzothiadiazole, thiophene S,S‘-dioxide, and dibenzothiophene S,S‘-dioxide as well as the extent of the π-conjugated core. As a result, their emission bands measured in chloroform can cover the full UV−vis spectrum (from 412 to 656 nm). In contrast to the common dipolar chromophores, most of OF(2)Ar-NPhs can form morphologically stable amorphous thin films (T g = 88−127 °C) with a high decomposition temperature, T dec > 450 °C. Remarkably, undoped OF(2)Ar-NPh-based multilayer OLEDs could exhibit good to excellent device performance with emission colors spanning the full UV−vis spectrum. OF(2)Ar-NPh bearing oligothiophene core based devices exhibit a maximum luminance of 5000−12500 cd m-2 and luminous efficiency up to 3.6−4.0 cd A-1. Our findings provide a practical approach to design and tune the color emission of efficient and potentially useful light emitting materials.

A novel ratiometric mitochondrial cysteine (Cys)-selective two-photon fluorescence probe has been developed on the basis of a merocyanine as the fluorophore and an acrylate moiety as the biothiol reaction site. The biocompatible and photostable acrylate-functionalized merocyanine probe shows not only a mitochondria-targeting property but also highly selective detection and monitoring of Cys over other biothiols such as homocysteine (Hcy) and glutathione (GSH) and hydrogen sulfide (H2S) in live cells. In addition, this probe exhibits ratiometric fluorescence emission characteristics (F518/F452), which are linearly proportional to Cys concentrations in the range of 0.5-40 μM. More importantly, the probe and its released fluorophore, merocyanine, exhibit strong two-photon excited fluorescence (TPEF) with two-photon action cross-section (Φσmax) of 65.2 GM at 740 nm and 72.6 GM at 760 nm in aqueous medium, respectively, which is highly desirable for high contrast and brightness ratiometric two-photon fluorescence imaging of the living samples. The probe has been successfully applied to ratiometrically image and detect mitochondrial Cys in live cells and intact tissues down to a depth of 150 μm by two-photon fluorescence microscopy. Thus, this ratiometric two-photon fluorescent probe is practically useful for an investigation of Cys in living biological systems.

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Novel deep‐blue‐light‐emitting diphenylamino and triphenylamino end‐capped oligofluorenes were synthesized by double palladium‐catalyzed Suzuki cross‐coupling of dibromo‐oligofluorene with the corresponding boronic acid as a key step. These oligofluorenes exhibit deep‐blue emission (λemmax = 429–432 nm), low and reversible electrochemical oxidation (highest occupied molecular orbital = 5.15–5.20 eV), high fluorescence quantum yield (ΦFL = 0.61–0.93), and good thermal properties (glass‐transition temperature, Tg = 99–195 °C and decomposition temperature, Tdec > 450 °C). Remarkably, saturated deep‐blue organic light‐emitting diodes, made from these oligofluorenes as dopant emitters, have been achieved with excellent performance and maximum efficiencies up to 2.9 cd A–1 at 2 mA cm–2 (external quantum efficiency of 4.1 %) and with Commission Internationale de l'Éclairage (x,y) coordinates of (0.152,0.08), which is very close to the National Television System Committee standard blue.

We have demonstrated that the subcellular targeting properties of the indole-based cyanines can be tuned by the functional substituent attached onto the indole moiety in which the first example of a highly RNA-selective and two-photon active fluorescent light-up probe for high contrast and brightness TPEF images of rRNA in the nucleolus of live cells has been developed. It is important to find that this cyanine binds much stronger toward RNA than DNA in a buffer solution as well as selectively stains and targets to rRNA in the nucleolus. Remarkably, the TPEF brightness (Φσmax) is dramatically increased with 11-fold enhancement in the presence of rRNA, leading to the record high Φσmax of 228 GM for RNA. This probe not only shows good biocompatibility and superior photostability but also offers general applicability to various live cell lines including HeLa, HepG2, MCF-7, and KB cells and excellent counterstaining compatibility with commercially available DNA or protein trackers.