No abstract

A blue iridium carbene complex realizes high‐efficiency blue and white OLEDs (see figure). For a blue OLED, ηp,max is recorded to be 35.9 lm W−1. For a white OLED, ηp,max and ηp,1000 are measured to be 59.9 lm W−1 and 43.3 lm W−1, respectively, without any light‐outcoupling enhancement. This white OLED also shows an illumination‐acceptable CRI over 80.

Recently, solid-state lighting has received considerable attention in both academic and industrial research. [1,2] Of particular interest, for the replacement of the existing light sources, are organic light-emitting diodes (OLEDs) based on phosphorescent molecules. [3][4][5][6] The advantage of using these materials lies in the possibility to internally convert all the spin uncorrelated injected charges into light. Indeed, an internal quantum efficiency of nearly 100% has been achieved in devices based on the green-emitting organometallic complex Ir(ppy) 3 .[7]However, many unresolved issues are the subject of current research in order to implement efficient white light sources and expand the number of applications. In particular, the origin of the efficiency roll-off at high voltages, [8][9][10] the light outcoupling, [11,12] the long-term stability [13,14] and the generation of white light with an all-phosphor device [6,15] are subjects under intense investigation. White light generation is a key issue because of the wide range of applications involving full-color displays and lighting. [1,2] Among the different approaches, solution processed devices based on white light emitting molecules [16] have been demonstrated as well as thermally evaporated red, green and blue (RGB) blends [15] or stacks. To date, white light OLEDs (WOLEDs) with long term operational lifetimes have been obtained mainly with a combination of a blue fluorescent emitter [6] and phosphors for the other colors. Such an elegant approach relies on a well engineered harvesting of singlet and triplet excitons and requires therefore a precise doping of the RGB emitting dyes in the transporting hosts. In contrast, efficient WOLEDs based on blue phosphors can be obtained with all the emitters in one single layer, [17] simplifying the processing. Generally, however, blue phosphors have in the past turned out to be rather unstable. While a physical explanation for blue phosphor based device instability is still lacking, a shorter phosphorescence lifetime, eventually approaching the sub-microsecond time regime, would decrease the residence time of potentially unstable excited states. Moreover, processes detrimental to the efficiency, such as exciton charge-carrier quenching [8] or triplet-triplet annihilation, [9,10] could be strongly reduced with a faster exciton recombination. A shorter phosphorescence lifetime while maintaining high quantum efficiencies requires a large radiative rate. For organometallic complexes this rate is directly proportional to the spin-orbit coupling (SOC) matrix element involving the emitting triplet and the perturbing singlet state and inversely proportional to the degree of mixing between them, i.e., the singlet-triplet splitting (DE ST ). [18][19][20] Photophysical studies of the role of SOC and DE ST in tuning the radiative rate are still sparse, mainly because the large intersystem crossing (ISC) rates ($10 13 s À1 ) of such phosphors, [21] which makes detection (and therefore direct measurement of DE ST ) rather cha...

A new detection scheme for catecholamines was constructed through embedding synthetic receptors within vesicles comprising phospholipids and polydiacetylene. Fluorescence emission of the polydiacetylene was induced through specific interactions between the soluble ligands and the vesicle-incorporated hosts. The system demonstrated remarkable selectivity among structurally similar ligands and achieved much lower detection thresholds compared to that of other reported catecholamine sensors. The chromatic assembly provides a generic route for high sensitivity detection of ligand-receptor interactions.

A new concept is introduced for the rational design of ␤-sheet ligands, which prevent protein aggregation. Oligomeric acylated aminopyrazoles with a donor-acceptor-donor (DAD) hydrogen bond pattern complementary to that of a ␤-sheet efficiently block the solvent-exposed ␤-sheet portions in A␤-(1-40) and thereby prevent formation of insoluble protein aggregates. Density gradient centrifugation revealed that in the initial phase, the size of A␤ aggregates was efficiently kept between the trimeric and 15-meric state, whereas after 5 days an additional high molecular weight fraction appeared. With fluorescence correlation spectroscopy (FCS) exactly those two, i.e. a dimeric aminopyrazole with an oxalyl spacer and a trimeric head-to-tail connected aminopyrazole, of nine similar aminopyrazole ligands were identified as efficient aggregation retardants whose minimum energy conformations showed a perfect complementarity to a ␤-sheet. The concentration dependence of the inhibitory effect of a trimeric aminopyrazole derivative allowed an estimation of the dissociation constant in the range of 10 ؊5 M. Finally, electrospray ionization mass spectrometry (ESI-MS) was used to determine the aggregation kinetics of A␤-(1-40) in the absence and in the presence of the ligands. From the comparable decrease in A␤ monomer concentration, we conclude that these ␤-sheet ligands do not prevent the initial oligomerization of monomeric A␤ but rather block further aggregation of spontaneously formed small oligomers. Together with the results from density gradient centrifugation and fluorescence correlation spectroscopy it is now possible to restrict the approximate size of soluble A␤ aggregates formed in the presence of both inhibitors from 3-to 15-mers.