Dimesitylborane as Electron Accepting Unit in High Performance Yellow Single-Layer Phosphorescent Organic Light Emitting Diode.

A new host material for Single-Layer Phosphorescent Organic Light-Emitting Diodes (SL-PhOLED) is reported, namely SPA-2-FDMB, using the dimesitylborane (DMB) fragment as an acceptor unit. The molecular design is constructed on the general donor-spiro-acceptor architecture, which consists of connecting, via a spiro bridge, a donor and an acceptor units in order to avoid strong interaction between them. The DMB fragment is known for many electronic applications (notably Aggregation-Induced Emission) but has not been used yet for SL-PhOLED applications.

Grafting Electron-Accepting Fragments on [4]cyclo-2,7-carbazole Scaffold: Tuning the Structural and Electronic Properties of Nanohoops.

Since the first applications of nanohoops in organic electronics appear promising, the time has come to go deeper into their rational design in order to reach high-efficiency materials. To do so, systematic studies dealing with the incorporation of electron-rich and/or electron-poor functional units on nanohoops have to be performed. Herein, the synthesis, the electrochemical, photophysical, thermal, and structural properties of two [4]cyclo-2,7-carbazoles, [4]C-Py-Cbz, and [4]C-Pm-Cbz, possessing electron-withdrawing units on their nitrogen atoms (pyridine or pyrimidine) are reported.

Modulation of [8]CPP properties by bridging two phenylene units.

We report the synthesis and characterization of two new fluorophores, consisting of a [8]cyclo--phenylene core in which two phenylenes are bridged by either a nitrogen atom or a carbonyl group. The nitrogen bridge increases the HOMO-LUMO gap, whereas the carbonyl bridge decreases it. These results provide guidelines to control the electronic properties of nanohoops.

Dihydroindenofluorenes as building units in organic semiconductors for organic electronics.

This review aims to discuss organic semiconductors constructed on dihydroindenofluorene positional isomers, which are key molecular scaffolds in organic electronics. Bridged oligophenylenes are key organic semiconductors that have allowed the development of organic electronic technologies. Dihydroindenofluorenes (DHIFs) belong to the family of bridged oligophenylenes constructed on a terphenyl backbone.

Electronic and Charge Transport Properties in Bridged versus Unbridged Nanohoops: Role of the Nanohoop Size.

In the field of π-conjugated nanohoops, the size of the macrocycle has a strong impact on its structural characteristics, which in turn affect its electronic properties. In this work, we report the first experimental investigations linking the size of a nanohoop to its charge transport properties, a key property in organic electronics. We describe the synthesis and study of the first example of a cyclocarbazole possessing five constituting building units, namely [5]-cyclo-N-butyl-2,7-carbazole, [5]C-Bu-Cbz.

Pure Hydrocarbon Materials as Highly Efficient Host for White Phosphorescent Organic Light-Emitting Diodes: A New Molecular Design Approach.

To date, all efficient host materials reported for phosphorescent OLEDs (PhOLEDs) are constructed with heteroatoms, which have a crucial role in the device performance. However, it has been shown in recent years that the heteroatoms not only increase the design complexity but can also be involved in the instability of the PhOLED, which is nowadays the most important obstacle to overcome. Herein, we design pure aromatic hydrocarbon materials (PHC) as very efficient hosts in high-performance white and blue PhOLEDs.

Evolution of pure hydrocarbon hosts: simpler structure, higher performance and universal application in RGB phosphorescent organic light-emitting diodes.

In the field of phosphorescent organic light-emitting diodes (PhOLEDs), designing high-efficiency universal host materials for red, green and blue (RGB) phosphors has been quite a challenge. To date, most of the high-efficiency universal hosts reported incorporate heteroatoms, which have a crucial role in the device performance. However, the introduction of different kinds of heterocycles increases the design complexity and cost of the target material and also creates potential instability in the device performance.

[4]Cyclo--alkyl-2,7-carbazoles: Influence of the Alkyl Chain Length on the Structural, Electronic, and Charge Transport Properties.

Macrocycles possessing radially oriented π-orbitals have experienced a fantastic development. However, their incorporation in organic electronic devices remains very scarce. In this work, we aim at bridging the gap between organic electronics and nanorings by reporting the first detailed structure-properties-device performance relationship study of organic functional materials based on a nanoring system.

[n]-Cyclo-9,9-dibutyl-2,7-fluorene (n=4, 5): Nanoring Size Influence in Carbon-Bridged Cyclo-para-phenylenes.

For the last ten years, ring-shaped π-conjugated macrocycles possessing radially directed π-orbitals have been subject to intense research. The electronic properties of these rings are deeply dependent on their size. However, most studies involve the flagship family of nanorings: the cyclo-para-phenylenes.

New generations of spirobifluorene regioisomers for organic electronics: tuning electronic properties with the substitution pattern.

The spirobifluorene (SBF) fragment constitutes one of the most important scaffolds used in the design of Organic Semi-Conductors (OSCs) for organic electronics. In the last ten years, new generations of SBF positional isomers have appeared in the literature. The different positions of substitution (C1, C3 or C4) have allowed the tuning of the electronic properties of great interest for the further design of functional materials.

Photoactive Boron-Nitrogen-Carbon Hybrids: From Azo-borazines to Polymeric Materials.

In this paper, we describe synthetic routes for preparing a novel switchable BNC-based chromophore, composed of a borazine core peripherally functionalized with azobenzene moieties. Capitalizing on the Pd-catalyzed Suzuki cross-coupling reaction between a tris-triflate borazine and an organoboron azobenzene derivative, a photoswtichable azo-borazine derivative was successfully prepared. The molecule showed reversible / photoisomerization upon irradiation at the maximum of the intense π-π* absorption feature (360 nm).

Cyclization of Terphenyl-Bisfluorenols: A Mechanistic Study of the Regioselectvity.

The mechanism of the bicyclization reaction of a series of terphenyl-bisfluorenols into dispiro[fluorene-9,6'-indeno[1,2-b]fluorene-12',9''-fluorene] and dispiro[fluorene-9,6'-indeno[2,1-a]fluorene-12',9''-fluorene] is reported. Through a combined experimental and theoretical study, the different parameters that drive the regioselectivity of this cyclization reaction have been studied and are presented.

[4]Cyclo-N-ethyl-2,7-carbazole: Synthesis, Structural, Electronic and Charge Transport Properties.

Nanorings, which are macrocycles possessing radially directed π-orbitals have shown fantastic development in the last ten years. Unravelling their unusual electronic properties has been one of the driving forces of this research field. However, and despite promising properties, their incorporation in organic electronic devices remains very scarce.

C1-Linked Spirobifluorene Dimers: Pure Hydrocarbon Hosts for High-Performance Blue Phosphorescent OLEDs.

Reported here are C1-linked spiro-bifluorene dimers. A comprehensive study is carried out to analyze the electronic properties of these highly twisted structures. This work shows that the C1-position enables the design of pure hydrocarbon materials, with a high triplet energy, for hosting blue phosphors in efficient phosphorescent OLEDs (PhOLEDs).

[4]Cyclofluorene: Unexpected Influence of Alkyl Chain Length.

Presented here is the study of a new example of [4]cyclofluorene, with ethyl chains on the bridgeheads. Its molecular structure was established by solution NMR spectroscopy and single-crystal X-ray diffraction. Three successive oxidation processes and one reversible reduction were observed through cyclic voltammetry.

Dihydroindenofluorene Positional Isomers.

Bridged oligophenylenes are very important organic semiconductors (OSCs) in organic electronics (OE). The fluorene unit, which is a bridged biphenyl, is the spearhead of this class of materials and has, over the last 20 years, led to fantastic breakthroughs in organic light-emitting diodes. Dihydroindenofluorenes belong to the family of bridged terphenyls and can be viewed as the fusion of a fluorene unit with an indene fragment.

A Dihydrodinaphthoheptacene.

We report the first example of a dihydrodinaphthoheptacene derivative and the mechanistic investigations of the regioselective electrophilic intramolecular cyclization reaction involved in the synthesis. The structural, electrochemical, and photophysical properties have been investigated.

Modulating the Physical and Electronic Properties over Positional Isomerism: The Dispirofluorene-Dihydroindacenodithiophene (DSF-IDT) Family.

We report the first studies on the intrinsic properties of a meta-substituted dihydroindacenodithienyl fragment and more generally the strong impact of positional isomerism on dihydroindacenodithiophene derivatives. The influence of the para and meta linkages has notably been highlighted not only for the electronic properties in solution (electrochemical properties, anodic polymerization, HOMO/LUMO energy levels, optical transitions, fluorescence spectra) but also on the physical properties in the solid state (molecular organization, crystallinity, and phase transitions). The positional isomerism hence appears to be a very efficient tool to drastically tune the properties of dihydroindacenodithiophene derivatives.

Spirobifluorene Regioisomerism: A Structure-Property Relationship Study.

The present works report the first structure-property relationship study of a key class of organic semiconductors, that is, the four spirobifluorene positional isomers possessing a para-, meta- or ortho-linkage. The remarkable and surprising impact of the ring bridging and of the linkages on the electronic properties of the regioisomers has been particularly highlighted and rationalised. The impact of the ring bridging on the photophysical properties has been stressed with notably the different influence of the linkages and the bridge on the singlet and triplet excited states.

Electron-Deficient Dihydroindaceno-Dithiophene Regioisomers for n-Type Organic Field-Effect Transistors.

In this work, we wish to report the first member of a new family of organic semiconductors constructed on a meta dihydroindacenodithiophene core, that is, 2,2'-(2,8-dihexyl-4,6-dihydro-s-indaceno[1,2-b:7,6-b']dithiophene-4,6-diylidene)dimalononitrile (called meta-IDT(═C(CN))). The properties of this molecule were studied in detail through a structure-properties relationship study with its regioisomer, that is, 2,2'-(2,7-dihexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-4,9-diylidene)dimalononitrile (para-IDT(═C(CN))) (see isomer structures in blue in Chart 2). The influence of the bridge functionalization was also investigated by comparison with their diketone analogues meta-IDT(═O) and para-IDT(═O).

Electron-Rich 4-Substituted Spirobifluorenes: Toward a New Family of High Triplet Energy Host Materials for High-Efficiency Green and Sky Blue Phosphorescent OLEDs.

We report herein a detailed structure-properties relationship study of the first examples of electron-rich 4-substituted spirobifluorenes for organic electronic applications, namely, 4-phenyl-N-carbazole-spirobifluorene (4-PhCz-SBF) and 4-(3,4,5-trimethoxyphenyl)-spirobifluorene (4-Ph(OMe)-SBF). The incorporation of the electron-rich moieties in the ortho position of the biphenyl linkage (position C4) induces unique properties, very different from those previously described in the literature for this family of semiconductors. Both dyes can be readily synthesized, possess high triplet energies and excellent thermal stability, and their HOMO energy levels are highly increased compared to those of other 4-substituted SBFs.

9H-Quinolino[3,2,1-k]phenothiazine: A New Electron-Rich Fragment for Organic Electronics.

A new electron-rich fragment, namely the quinolinophenothiazine (QPTZ) is reported. The QPTZ fragment incorporated in spiroconfigured materials leads to higher performance in blue Phosphorescent OLEDs than structurally related phenylacridine and indoloacridine based materials (increasing the HOMO energy level, modulating the spin-orbit coupling, etc.) and leads to highly efficient blue phosphorescent organic light emitting diodes, indicating the strong potential of this new molecular fragment in organic electronics.

Modulation of the Physicochemical Properties of Donor-Spiro-Acceptor Derivatives through Donor Unit Planarisation: Phenylacridine versus Indoloacridine-New Hosts for Green and Blue Phosphorescent Organic Light-Emitting Diodes (PhOLEDs).

This work reports a detailed structure-property relationship study of a series of efficient host materials based on the donor-spiro-acceptor (D-spiro-A) design for green and sky-blue phosphorescent organic light-emitting diodes (PhOLEDs). The electronic and physical effects of the indoloacridine (IA) fragment connected through a spiro bridge to different acceptor units, namely, fluorene, dioxothioxanthene or diazafluorene moiety, have been investigated in depth. The resulting host materials have been easily synthesised through short, efficient, low-cost, and highly adaptable synthetic routes by using common intermediates.

Spirobifluorene-2,7-dicarbazole-4'-phosphine Oxide as Host for High-Performance Single-Layer Green Phosphorescent OLED Devices.

A new host material based on the 2,7,4'-substituted spirobifluorene platform has been designed and used in single-layer phosphorescent OLED with very high efficiency (EQE = 13.2%) and low turn-on voltage (2.4 V).

Donor/Acceptor Dihydroindeno[1,2-a]fluorene and Dihydroindeno[2,1-b]fluorene: Towards New Families of Organic Semiconductors.

New families of donor/acceptor semiconductors based on dihydroindeno[1,2-a]fluorene and dihydroindeno[2,1-b]fluorene are reported. Due to the spiro bridges, this new generation of dihydroindenofluorenes allows a spatial separation of HOMO and LUMO, which retains the high ET value of the dihydroindenofluorene backbone and excellent physical properties. This control of the electronic and physical properties has allowed a second generation of dihydroindeno[1,2-a]fluorene to be obtained with strongly enhanced performance in green and sky-blue phosphorescent organic light-emitting diodes (PhOLEDs) relative to the first generation of materials.