Introduction: Branched macromolecules or dendrimers have provided a rich seam of research in terms of both innovative chemistry and applications.1-14 For example, dendrimers have been studied for use as low-dielectric materials,15 as templates for the growth of single-wall carbon nanotubes,16 as catalysts,17-19 and in biological applications,20-23 including biosensors,24 magnetic resonance imaging,25-28 and drug delivery.29-33 However, it has only been more recently that such macromolecular structures have been explored in terms of their electronic and optoelectronic properties, which is the focus of this series of reviews. For example, charge-transporting dendrimers have become an important class of organic semiconducting material34 and significant effort has focused on light harvesting and energy transfer from a peripheral dye or chromophore to an emissive dye at the center or focus of the dendrimer.35-39 Organic semiconductors have become increasingly important as the active component in applications including organic light-emitting diodes (OLEDs),40-42 transistors,43,44 photovoltaic (PV) cells,45,46 optical amplifiers,47,48 and lasers.49-51 Traditionally, organic semiconductors have fallen into two main classes, small molecules and polymers, and these materials and their applications will be covered in detail by other authors. Small molecules are generally processed by evaporation techniques and have the advantages that the structure−property relationships are relatively simple to understand, the materials are mono(disperse), and they are deposited in a pure form. On the other hand, conjugated polymers are soluble and can be deposited from solution by processes such as spin-coating and ink-jet printing, which opens up the exciting prospect of simple, fast, large-area, low-temperature device manufacturing. An additional advantage for conjugated polymers is that solution processing is potentially less wasteful of material than evaporation for devices that require patterning. However, it is often difficult to control the polydispersity, molecular weight, backbone defects, and end groups of conjugated polymers reproducibly. Branched macromolecules, known as dendrimers, also have the advantage of being solution processable but by careful design can incorporate the control over the optoelectronic properties that is reminiscent of small molecules. In addition, the dendritic architecture provides a number of other attractive properties, including the ability to independently control the processing and optoelectronic properties; providing the processing power to enable simple chromophores to be deposited as stable amorphous films; dendrimer generation as a tool for controlling the intermolecular interactions that govern device performance; and the ability in well-defined dendrimers to have high chemical purity. In this review, we will focus on synthetic strategies that have been investigated for the preparation of optoelectronically active solution-processable dendritic materials and concentrate on two different applications, namely OLEDs and solar cells, in which they have been used. In the context of OLEDs, we limit the discussion to light emission, as branched macromolecules for charge transport will be discussed in the review by Shirota. We will also briefly comment on other recent light-emitting and -absorbing branched molecular materials that have been used in OLEDs and solar cells.

Development of Dendrimers: Macromolecules for Use in Organic Light-Emitting Diodes and Solar Cells

The present invention relates to compounds of the formula (1) which are suitable for use in electronic devices, in particular organic electroluminescent devices, and to electronic devices which contain these compounds.

Materials for organic electroluminescent devices

One of the requirements for efficient organic electroluminescent devices (OLEDs) is balanced charge injection from the two electrodes and efficient transport of both holes and electrons within the luminescent layer in the device structure. Many of the common luminescent conjugated polymers, e.g. derivatives of poly(phenylenevinylene) and poly(fluorene), are predominantly hole transporters (i.e. p-dopable). This article gives a brief overview of organic electroluminescence and electrophosphorescence and provides a more detailed consideration of ways in which electron transport in these systems has been enhanced by the incorporation of electron-deficient (i.e. n-dopable) small molecules and polymers into the devices, either as blends or by covalent attachment of sub-units to the luminophore or as an additional electron-transporting, hole-blocking (ETHB) layer adjacent to the cathode. The chemical structures of these systems are presented and their roles are assessed. Most of these ETHB molecules are electron-deficient aromatic nitrogen-containing heterocycles, e.g. derivatives of 1,3,4-oxadiazole, pyridine, pyrimidine, pyrazine, quinoline, etc. Non-aromatic thiophene-S,S-dioxide derivatives are also discussed. The article is written from an organic chemist's perspective.

Electron-transporting materials for organic electroluminescent and electrophosphorescent devices

Porous, fluorescent, covalent triazine-based frameworks (CTFs) are obtained in an unprecedentedly mild reaction, opening up a scalable pathway for molecular building blocks previously thought incompatible with this chemistry. Choice of monomers and synthetic conditions determines the optical properties and nano-scale ordering of these highly microporous materials with BET surface areas exceeding 1100 m(2) g(-1) and exceptional CO(2) capacities (up to 4.17 mmol g(-1)).

Porous, Fluorescent, Covalent Triazine-Based Frameworks Via Room-Temperature and Microwave-Assisted Synthesis

An aromatic anion receptor: anion-pi interactions do exist.

Four novel blue luminescent star-shaped compounds 1,3,5-tris(di-2-pyridylamino)benzene, 1, 1,3,5-tris[p-(di-2-pyridylamino)phenyl]benzene, 2, 2,4,6-tris(di-2-pyridylamino)-1,3,5-triazine, 3, and 2,4,6-tris[p-(di-2-pyridylamino)phenyl]-1,3,5-triazine, 4, have been synthesized and fully characterized. Compounds 1, 2 and 4 were prepared from the reactions of appropriate s-triazine and 1,3,5-trisubstituted benzene compounds with di-2-pyridylamine via copper-mediated Ullmann condensation in good yield (45–85%). Compounds 1, 2
and 4 show glass formation. Compounds 1–4 emit a blue color both in solution and in the solid state. The emission maxima of compounds 1–4 in the solid state are at λ = 412, 409, 393 and 440 nm, respectively. Fluorescence quantum yields of compounds 1–4 are 0.53, 0.16, 0.43 and 0.78, respectively. Electroluminescent devices using compounds 1–4 as the emitters were fabricated.

Xiao-Ping Yang

Papers

Syntheses, structures, and electroluminescence of new blue luminescent star-shaped compounds based on 1,3,5-triazine and 1,3,5-trisubstituted benzene