We present a novel core-shell-surface multifunctional structure for dendrimers using a blue fluorescent pyrene core with triphenylene dendrons and triphenylamine surface groups. We find efficient excitation energy transfer from the triphenylene shell to the pyrene core, substantially enhancing the quantum yield in solution and the solid state (4-fold) compared to dendrimers without a core emitter, while TPA groups facilitate the hole capturing and injection ability in the device applications. With a luminance of up to 1400 cd/m(2), a saturated blue emission CIE(xy) = (0.15, 0.17) and high operational stability, these dendrimers belong to the best reported fluorescence-based blue-emitting organic molecules.

The complex interaction between an ultrasound-driven microbubble and an enclosing capillary microvessel is investigated by means of a coupled, multidomain numerical model using the finite volume formulation. This system is of interest in the study of transient blood-brain barrier disruption (BBBD) for drug delivery applications. The compliant vessel structure is incorporated explicitly as a distinct domain described by a dedicated physical model. Red blood cells (RBCs) are taken into account as elastic solids in the blood plasma. We report the temporal and spatial development of transmural pressure (P tm ) and wall shear stress (WSS) at the luminal endothelial interface, both of which are candidates for the yet unknown mediator of BBBD. The explicit introduction of RBCs shapes the P tm and WSS distributions and their derivatives markedly. While the peak values of these mechanical wall parameters are not affected considerably by the presence of RBCs, a pronounced increase in their spatial gradients is observed compared to a configuration with blood plasma alone. The novelty of our work lies in the explicit treatment of the vessel wall, and in the modelling of blood as a composite fluid, which we show to be relevant for the mechanical processes at the endothelium.

Thorough analyses of the photo-and devicephysics of by the means of absorption and photoluminescence emission, time resolved photoluminescence and photoinduced absorption spectroscopy as well as organic light emitting devices (OLEDs) are presented in this contribution. Thereby we find that this novel class of polymers shows deep blue light emission as required for OLEDs and does not exhibit excimer or aggregate emission when processed from solvents with low polarity. Moreover the decay dynamics of the compound is found to be comparable to that of well blue emitting conjugated polymers such as polyfluorene. OLEDs built in an improved device assembly show stable bright blue emission for the PPyr homopolymer and further a considerable efficiency enhancement can be demonstrated using a triphenylamine(TPA)/pyrene copolymer. ©2011 Optical Society of America

Wiedemair et al. Phys. Fluids 26, 062106 (2014) The response of individual MBs in an infinite liquid volume to an incident US field has been studied extensively 10 and is analytically described. 11 Moreover, some aspects of MB dynamics in a confined space can be predicted. 12 The non-linear response of MBs to increasing levels of ultrasound excitation was examined by Lauterborn 13 employing frequency response curves. In the last decade experimental investigations 14 have profited from the availability of ultra-high frame rate cameras. 15 However, capturing the small length scales and the rapid vibrations of MBs in the MHz frequency range remains challenging, especially when multiple bubbles are considered. The force resulting from a spatial pressure gradient acting on a vibrating bubble was investigated by Bjerknes. 16 This gradient may either be created by an external source, giving rise to the primary Bjerknes force (f B1), or caused locally by the vibrations of a neighboring bubble, resulting in the secondary Bjerknes force (f B2). The interaction of two MBs is governed by the latter force, which, according to linear theory, determines mutual attraction or repulsion depending on the difference in vibration phase. 17 For simplified systems where the MBs retain a spherical shape throughout the oscillation cycle and are spaced sufficiently far apart, the dynamics can be studied by analytical means. 18, 19 Most derivations assume viscous, incompressible host liquids, and adiabatically compressible bubbles. 20-22 Non-spherical oscillations of MBs in close proximity in an inviscid, incompressible liquid were studied by Pelekasis and Tsamopoulos 23 using Legendre modes. The influence of non-linear pulsations on the translation direction was investigated by Oguz and Prosperetti 19 using a virial theorem approach which was further developed and refined by Harkin et al. 24 Doinikov 25 proposed a model for the time-averaged dynamics of multiple bubbles spaced at arbitrary distances and specifically addresses the time-averaged force of closely spaced air bubbles in an inviscid fluid. 26 The direction of this force depends also on the distance between the MBs 22 and the excitation amplitude. 18 A detailed review of the topic is provided by Doinikov. 27 Experimental observations of f B2 are reported by Garbin et al., 28 who studied the impact of close-by walls or neighboring MBs on the oscillation pattern of an MB. Marmottant et al. 29 investigated the oscillatory and translator dynamics of a MB interacting with a wall using ultra-fast imaging technologies. 15 Yoshida et al. 30 reported the observation of changes in direction of the relative motion of two MBs and its dependence on their distance. The aggregation of stable bubble clusters, 31 called bubble grapes, could be related to this phenomenon. 32 Volume of fluid, 33 level set, 34 and front tracking 35, 36 methods have been proposed to describe the bubble interface, for example, in the modeling of rising macroscopic gas bubbles. 37-41 An interface tracking algorithm em...

Encapsulated microbubbles (MBs) serve as endovascular agents in a wide range of medical ultrasound applications. The oscillatory response of these agents to ultrasonic excitation is determined by MB size, gas content, viscoelastic shell properties and geometrical constraints. The viscoelastic parameters of the MB capsule vary during an oscillation cycle and change irreversibly upon shell rupture. The latter results in marked stress changes on the endothelium of capillary blood vessels due to altered MB dynamics. Mechanical effects on microvessels are crucial for safety and efficacy in applications such as focused ultrasound-mediated blood-brain barrier (BBB) opening. Since direct in vivo quantification of vascular stresses is currently not achievable, computational modelling has established itself as an alternative. We have developed a novel computational framework combining fluid-structure coupling and interface tracking to model the nonlinear dynamics of an encapsulated MB in constrained environments. This framework is used to investigate the mechanical stresses at the endothelium resulting from MB shell rupture in three microvessel setups of increasing levels of geometric detail. All configurations predict substantial elevation of up to 150 % for peak wall shear stress upon Zurich Center for Integrative Human Physiology, and Neuroscience Center Zurich, University of Zurich, Zurich, Switzerland MB breakup, whereas global peak transmural pressure levels remain unaltered. The presence of red blood cells causes confinement of pressure and shear gradients to the proximity of the MB, and the introduction of endothelial texture creates local modulations of shear stress levels. With regard to safety assessments, the mechanical impact of MB breakup is shown to be more important than taking into account individual red blood cells and endothelial texture. The latter two may prove to be relevant to the actual, complex process of BBB opening induced by MB oscillations.