Red‐shifting beyond red: The nonplanar porphyrin complex Pt(tpbp) (tpbp=tetraphenyltetrabenzoporphyrin) has been used as a phosphorescent dopant in highly efficient electrophosphorescent devices that ...emit in the near‐infrared region (see normalized emission spectrum). The high efficiencies of these NIR devices make them amenable to many night‐vision display and sensing applications.
A new thermally cross-linkable copolymer containing reactive benzocyclobutene (BCB) units and the well-known hole-transporting moiety N,N‘-bis(3-methylphenyl)-N,N‘-diphenylbenzidine) (TPD) was ...synthesized and characterized. Thermal annealing of spun-cast films of the copolymer, followed by cross-linking at 200 °C, led to insoluble polymer films with a smooth surface. Green emitting fluorescent OLEDs were fabricated using the new cross-linkable polymer and compared with conventionally prepared devices. Using the thermally cross-linked copolymer as a hole-transporting layer, solution processed multilayer light emitting diodes were prepared that exhibited high performance with 10.4% external quantum efficiency at a brightness of 350 cd/m2.
We report a formulation of near-infrared (near-IR) phosphorescent polymeric nanomicelles and their use for in vivo high-contrast optical imaging, targeting, and detection of tumors in small animals. ...Near-IR phosphorescent molecules of Pt(II)−tetraphenyltetranaphthoporphyrin (Pt(TPNP)) were found to maintain their near-IR phosphorescence properties when encapsulated into phospholipid nanomicelles. The prepared phosphorescent micelles are of ∼100 nm size and are highly stable in aqueous suspensions. A large spectral separation between the Pt(TPNP) absorption, with a peak at ∼700 nm, and its phosphorescence emission, with a peak at ∼900 nm, allows a dramatic decrease in the level of background autofluorescence and scattered excitation light in the near-IR spectral range, where the signal from the phosphorescent probe is observed. In vivo animal imaging with subcutaneously xenografted tumor-bearing mice has resulted in high contrast optical images, indicating highly specific accumulation of the phosphorescent micelles into tumors. Using optical imaging with near-IR phosphorescent nanomicelles, detection of smaller, visually undetectable tumors has also been demonstrated.
Small‐molecule solar cells are demonstrated using Pt and Pd tetraphenylbenzoporphyrin as donor materials. High efficiencies are achieved, and the effects of triplet excited state diffusion are ...studied. The solubility of these molecules allows for the fabrication of solution processed solar cells with relatively high performance.
We explore the dependence of the dark current of C60-based organic photovoltaic (OPV) cells on molecular composition and the degree of intermolecular interaction of several molecular donor materials. ...The saturation dark current density, J S, is an important factor in determining the open circuit voltage, V oc. The V oc values of OPVs show a strong inverse correlation with J S. Donor materials that show evidence for aggregation in their thin-film absorption spectra and polycrystallinity in thin film X-ray diffraction result in a high dark current, and thus a low V oc. In contrast, donor materials with structures that hinder intermolecular π-interaction give amorphous thin films and reduced values of J S, relative to donors with strong intermolecular π-interactions, leading to a high V oc. This work provides guidance for the design of materials and device architectures that maximize OPV cell power conversion efficiency.
Rotverschiebung über Rot hinaus: Der nichtplanare Porphyrinkomplex Pt(tpbp) (tpbp=Tetraphenyltetrabenzoporphyrin) wurde als phosphoreszierendes Dotierungsmittel in hocheffizienten ...elektrophosphoreszierenden Bauteilen eingesetzt, die im Nah‐IR‐Bereich emittieren (siehe normiertes Emissionsspektrum). Die hohen Effizienzen lassen diese NIR‐Funktionseinheiten für Nachtsichtanzeigen und Sensoren geeignet erscheinen.
This dissertation describes the development of interesting materials for different organic layers, which compose the standard organic light emitting diode (OLED) architecture. Chapter one introduces ...the OLEDs architecture, energy transfer mechanisms within the OLED and current – voltage behavior. The first part of chapter two deals with the photoinitiated cationic radical polymerization of cross-linkable monomeric compounds for solution processable hole-transporting layers. These solutions where subjected to UV irradiation and the polymerization process monitored by the disappearance of characteristic IR-Bands using FTIR spectroscopy. The second part of chapter two deals with thermally cross-linkable hole-transporting polymers based on 4-vinyl-benzocyclobutene and, 4-N-(4-vinylphenyl)- N-(4-methylphenyl)amino-4-N-phenyl-N-(4 methylphenyl)-amino-biphenyl or 3-vinyl-triphenylamine. These polymer films were thermally annealed for 2 h at 170 °C followed by cross-linking at 210 °C for 5 h. OLED devices were made by vacuum deposition of aluminum tris(8-hydroxyquinoline) acting as both the emitting- and electron injection layer on top of spin-coated cross-linked, non-cross-linked, and homopolymer hole-transporting layers. The results obtained were compared with small molecule vacuum deposited TPD, a common hole transporting material used in devices today. Chapter three deals with phosphorescent complexes employed as dopants in nIR emitting OLEDs. A family of metal complexes that have shown intense absorption and emission in the red-to-near infrared region of the electromagnetic spectrum are metalloporphyrins. In this chapter we studied the photophysical and electroluminescence properties of two Pt-metalloporphyrins; Pt(II)- tetraphenyltetrabenzoporphyrin and Pt(II)-tetraphenyltetranaphthoporphyrin. Chapter four describes the rational large scale synthesis of asymmetric porphyrins to provide a phosphorescence dopant for the application in organic light emitting diode. These asymmetric porphyrins are expected to have a phosphorescence emission maximum between those reported for Pt(II)(tetraphenylbenzoporphyrin) and Pt(II)(tetraphenylnaphthoporphyrin). Do to scrambling during the porphyrin formation reaction, systematic synthesis of different asymmetric porphyrins was not possible on large scale without extensive work on improving the reaction conditions in order to minimize scrambling and product purification efforts. Thus a statistical synthetic approach was chosen along with HPLC purification to identify specific asymmetric compounds and to investigate their corresponding phosphorescence emission energies. Chapter 5 describes host materials for OLEDs. The most common design for phosphorescence-based OLEDs involves a doped emissive region, where the emissive dopant is either an Ir or a Pt complex. While high-efficiency green and red emitting colors could be obtained readily by doping in the commonly used host materials, such as tris(8-hydroxyquinolinato)aluminum (Alq 3), a wider band gap host is essential for the efficient generation of blue dopant emission. Cyclooctatetraene (COT) is a highly interesting class of organic molecules and despite having the same (CH)n formulation, benzene and COT have strikingly different properties for example, COT is a non-planar tub-shaped molecule. But, the reduction of COT is accompanied by a structural change of the tub shaped neutral molecule to a planar ring, which has been both studied computationally and spectroscopically. For this reason, the geometry of the COT has to be locked into place in order to keep the high triplet energy need for efficient energy transfer to the blue phosphorescent dopant. This may be accomplished through the addition of bulky substituents to the COT scaffold.
Recently there has been a growing interest in OLEDs that emit in the near infrared region (700–1250nm) for covert night vision applications. Here we report our results on a highly efficiency ...phosphorescent metalloporphyrin OLED device with a λmax= 765 nm. We will demonstrate a bi‐color day/ covert night active matrix display fabricated on flexible metal using this material for the IR pixel.
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