Understanding the excited-state dynamics and conformational relaxation in thermally activated delayed fluorescence (TADF) molecules, including conformations that potentially support intramolecular through-space charge transfer, can open new avenues for TADF molecular design as well as elucidate complex photophysical pathways in structurally complex molecules. Emissive molecules comprising a donor (triphenylamine, TPA) and an acceptor (triphenyltriazine, TRZ) bridged by a second donor (9,9-dimethyl-9-10-dihydroacridin, DMAC, or phenoxazine, PXZ) are synthesized and characterized. In solution, the flexibility of the sp 3 -hybridized carbon atom in DMAC of DMAC–TPA–TRZ , compared to the rigid PXZ, allows significant conformational reorganization, giving rise to multiple charge-transfer excited states. As a result of such a reorganization, the TRZ and TPA moieties become cofacially aligned, driven by a strong dipole–dipole attraction between the TPA and TRZ units, forming a weakly charge-transfer dimer state, in stark contrast to the case of PXZ–TPA–TRZ where the rigid PXZ bridge only supports a single PXZ–TRZ charge transfer (CT) state. The low-energy TPA-TRZ dimer is found to have a high-energy dimer local triplet state, which quenches delayed emission because the resultant singlet CT local triplet energy gap is too large to mediate efficient reverse intersystem crossing. However, organic light-emitting diodes using PXZ–TPA–TRZ as an emitting dopant resulted in external quantum efficiency as high as 22%, more than two times higher than that of DMAC–TPA–TRZ -based device, showing the impact that such intramolecular reorganization and donor–acceptor dimerization have on TADF performance.

We report a systematic study of charge transport in a range of low-molar-mass and extended (having at least six aromatic rings) nematic liquid crystals, some of which are reactive mesogens, with a high degree of shape anisotropy, i.e., the length-to-width (aspect) ratio is exceptionally high. We demonstrate that the hole mobility is independent of the macroscopic, but not microscopic, ordering of the nematic and isotropic phases of these nematic liquid crystals with a long, rigid, and extended aromatic molecular core, because no discontinuity is observed at the transition between these phases. A room-temperature mobility of up to 1.0 × 10-3 cm2 V-1 s-1 is obtained in the nematic phase, which is attributed to the short intermolecular distances between the highly polarizable but rigid long aromatic cores. We show that the intermolecular separation can be easily fine-tuned by changing the lateral and terminal aliphatic groups of these nematic liquid crystals. Hence, the charge mobility can be varied by up to 2 orders of magnitude without altering the core structure of the molecules, and this chemical fine control could be used to limit hole transport and so provide better charge balance in organic light-emitting diodes. X-ray diffraction is used to obtain the intermolecular separation and shows local lamellar order in the nematic phase.

In this paper we demonstrate how the photonic properties of a diatom can be altered by growth with a metal pollutant. Both the optical and physical properties of the silica frustule of the diatom Coscinodiscus wailesii were affected by the presence of nickel sulfate in sea water. It was found that a sublethal concentration of the metal both significantly modified the size of the pores of the valves and quenched the intrinsic PL of the amorphous silica. Since cytoplasmic structures may be involved in determining the frustule architecture, we also present TEMs of nickel-grown diatoms and show the affected organelles. The ability to modify the properties of the frustule shows that mechanisms exist for the alteration of existing structures in nature to optimize specific characteristics for exploitation in biotechnological applications.

free them from inhibitors prior to use. GPC was performed with a Waters system using polystyrene standards and THF as the mobile phase.Microgel Preparation: Monomers were mixed in the desired ratios (Table 1) in a round-bottom flask. The resulting mixtures (6 g) were diluted with the prescribed amount of cyclopentanone. 0.18 g (3 wt.-% with respect to the monomer mixture) azobis(isobutyronitrile) (AIBN) were then added. The resulting solution was degassed, put under nitrogen, and placed for 72 h in a thermostated oil bath preheated at 80 C. The polymerization solution was concentrated to about 1/4 of the original volume and subsequently poured in the fivefold volume of petroleum ether under efficient stirring. The precipitated solid was filtered off and dried under vacuum to constant weight. Yields were in all cases greater than 85 %.Preparation of Pd Nanoclusters: 1 g microgel was dissolved in 20 mL dichloromethane under an inert atmosphere. A solution of 48 mg Pd(OAc) 2 (0.25 equiv with respect to the available amino groups, 2.4 wt.-% Pd) in 10 mL dichloromethane was then added, and the resulting solution was stirred at room temperature overnight. Subsequently, the reduction of the metal precursor was performed by two different methods: 1) the solution was heated at reflux and 6 mL ethanol were added under stirring. Stirring was continued for 12 h, after which the nanocluster-containing microgel was precipitated by pouring the solution in petroleum ether. 2) 2 mL NaHBEt 3 (1 M solution in THF) were added and the resulting solution was stirred at room temperature for 1 day, after which the nanocluster-containing microgel was precipitated by pouring the solution into petroleum ether.Preparation of Pt Nanoclusters: 1 g microgel was dissolved in 20 mL acetonitrile under an inert atmosphere. A solution of 74 mg PtCl 2 (CH 3 CN) 2 (0.25 equiv with respect to the available amino groups) in 10 mL dichloromethane was then added, and the resulting solution was stirred at room temperature for 24 h. 2 mL NaHBEt 3 (1 M solution in THF) were added and the resulting solution was stirred at room temperature for 1 day, after which the nanoclustercontaining microgel was precipitated by pouring the solution into diethyl ether.Catalytic Tests: 10 mmol aryl halide, 0.84 g (10 mmol) NaOAc, 47 mg catalyst (0.01 mmol Pd), and 25 mL N,N-dimethylacetamide were mixed at room temperature in a three-necked round-bottom flask equipped with a reflux condenser. The resulting mixture was degassed and put under a nitrogen atmosphere. 17 mmol n-butylacrylate were added and the flask was put in an oil bath at 120 C and stirred for 1 h. One of the fascinating aspects of chiral nematic liquid crystals is their vivid color resulting from selective reflection of circularly polarized light with the same handedness as the liquid crystal. The self-assembly of the uniformly aligned helical structures establishes a one-dimensional (1D) photonic stop band reflecting circularly polarized light of wavelength matching the helical pitch. There are a number of ...

The clinical performance of the SLMA as a ventilatory device is comparable with that of the PLMA, as illustrated by the similar LSPs. The inferior position of the SLMA airway tube compared with that of the PLMA does not affect its ease of ventilation.

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Light-emitting nematic liquid crystals are promising materials for organic light-emitting devices because their orientational anisotropy allows polarized electroluminescence and improved carrier transport. Two classes of nematics, i.e., room-temperature glasses and crosslinked polymer networks are discussed. The latter class has an additional advantage in that photolithography can be used to pixelate a full-color display. We show that the order parameter and birefringence of a new light-emitting nematic liquid crystal with an extended aromatic core both have values greater than 0.9. The performance of green light-emitting devices incorporating liquid crystals of different conjugation lengths is discussed. Efficacies up to 11.1 cd/A at 1160 cd/m 2 at an operating voltage of 7 V were obtained. A spatially graded, color organic light-emitting device obtained by overlapping pixels of blue-, green-, and red-emitting liquid crystals were demonstrated. Some regions of the red pixel were only partially photopolymerized in order to obtain different hues in the overlapping region with green. We also show that the photolithographic process has micron-scale resolution.

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