Platinum(II) complexes with cyclometallated 5-pi-delocalized-donor-1,3-di(2-pyridyl)benzene ligands as efficient phosphors for NIR-OLEDs

Two new pincer proligands, namely 5-(p-(N,N-diphenylamino)phenylethynyl)-1,3-di(2-pyridyl)benzene (HL1) and trans-5-(p-(N,N-diphenylamino)styryl-1,3-di(2-pyridyl)benzene (HL2) were prepared together with their N^C^N-coordinated cyclometallated platinum(II) complexes PtL1X (X = Cl, NCS) and PtL2Cl. Both ligands are intensely luminescent in solution (quantum yields > 0.8). PtL1X complexes display high quantum yields in solution whereas that of PtL2Cl is very low due to the ease with which trans to cis isomerisation of the diphenylaminostyryl C[double bond, length as m-dash]C bond occurs. Distinct sets of emission bands attributable to the cis and trans forms are observable in glass at 77 K, the assignments being supported by TD-DFT calculations. Organic light-emitting diodes (OLEDs) have been prepared using the new compounds as phosphorescent emitters. Remarkably, despite the inferior quantum yield of PtL2Cl in solution, the best electroluminescence quantum efficiencies are obtained with this complex, which emerges as an excellent candidate for the preparation of NIR-OLEDs

OLEDs based on multi-emission by a single emitter

Organic light-emitting diodes (OLEDs) are solid state thin film devices composed of stacked organic layers sandwiched between two electrodes. Light is generated in the electroluminescent layer containing an emissive (for example metal complex or polymer). Generally, in order to generate white-light emitting OLED (WOLED), the OLED organic stack has to contain red, green and blue emitters. Herein, we report WOLED where a platinum complex having di(2-pyridinyl)benzene-based tridentate ligand is the only emitter in the emitting layer. The Pt complex, which emits in the blue region, has a planar structure and thus has a tendency to form luminescent red-shifted aggregates. At the concentration of 20% in the emitting layer, the balanced contributions of monomeric and aggregate emissions of the Pt complex yield white light. The performance of WOLEDs devices of new architecture was studied. Luminance reaches 18000 cd/m2 and external electroluminescent efficiency is 7%. White light emitted by the devices is characterized by CIE (0.42, 0.38) and CRI = 65

Monolayers of Silver Nanoparticles Decrease Photobleaching: Application to Muscle Myofibrils

Studying single molecules in a cell has the essential advantage that kinetic information is not averaged out. However, since fluorescence is faint, such studies require that the sample be illuminated with the intense light beam. This causes photodamage of labeled proteins and rapid photobleaching of the fluorophores. Here, we show that a substantial reduction of these types of photodamage can be achieved by imaging samples on coverslips coated with monolayers of silver nanoparticles. The mechanism responsible for this effect is the interaction of localized surface plasmon polaritons excited in the metallic nanoparticles with the transition dipoles of fluorophores of a sample. This leads to a significant enhancement of fluorescence and a decrease of fluorescence lifetime of a fluorophore. Enhancement of fluorescence leads to the reduction of photodamage, because the sample can be illuminated with a dim light, and decrease of fluorescence lifetime leads to reduction of photobleaching because the fluorophore spends less time in the excited state, where it is susceptible to oxygen attack. Fluorescence enhancement and reduction of photobleaching on rough metallic surfaces are usually accompanied by a loss of optical resolution due to refraction of light by particles. In the case of monolayers of silver nanoparticles, however, the surface is smooth and glossy. The fluorescence enhancement and the reduction of photobleaching are achieved without sacrificing the optical resolution of a microscope. Skeletal muscle myofibrils were used as an example, because they contain submicron structures conveniently used to define optical resolution. Small nanoparticles (diameter ∼60 nm) did not cause loss of optical resolution, and they enhanced fluorescence ∼500-fold and caused the appearance of a major picosecond component of lifetime decay. As a result, the sample photobleached ∼20-fold more slowly than the sample on glass coverslips