Joëlle Rault-Berthelot

Phosphole‐Containing π‐Conjugated Systems: From Model Molecules to Polymer Films on Electrodes

Two series of 2,5-dipyridyl- and 2,5-dithienylphosphole derivatives containing sigma3- or sigma4-P atoms were prepared, and their optical (UV/Vis absorption, fluorescence spectra) and electrochemical properties were systematically evaluated. These physical properties depend mainly on the natures of the 2,5-substituents and of the phosphorus moiety, and they revealed that these compounds contain extended pi-conjugated systems. Structure-property relationships were established on the basis of these experimental data and ab initio calculations on the parent molecules. The limited aromatic character and low-lying LUMO of the phosphole ring appear to be crucial for achieving a highly delocalised pi system. Electrooxidation of 2,5-dithienylphosphole derivatives affords electroactive films with low optical band gaps. As observed for the corresponding monomers, the optical and electrochemical properties of the polymers can be varied over a wide range by modifying the nature of the phosphorus moiety.

ortho‐, meta‐, and para‐Dihydroindenofluorene Derivatives as Host Materials for Phosphorescent OLEDs

This work reports the first structure-properties relationship study of ortho [2,1-c]-, meta [1,2-a]-, and para [1,2-b]dihydroindenofluorenes, highlighting the influence of bridge rigidification on the electronic properties. This study has made it possible to devise an extended π-conjugated molecule with both a high triplet state energy level and excellent thermal and morphological stability. As a proof of concept, dihydroindenofluorenes were used as the host in sky-blue phosphorescent organic light-emitting diodes (PhOLEDs) with high performance.

Intramolecular excimer emission as a blue light source in fluorescent organic light emitting diodes: a promising molecular design

Intramolecular excimer emission arising from organic molecules as a blue light source in fluorescent Small Molecule Organic Light Emitting Diodes (SMOLEDs) is almost absent from the literature. In this work, three aryl-substituted DiSpiroFluorene–IndenoFluorenes (DSF–IFs 1–3) possessing different fluorescent properties due to their different main emitters have been investigated through a structure–property relationship study. Due to its particular geometry, the rigid DSF–IF platform 2 allows an ‘aryl/fluorene/aryl’ dimer to be preformed in the ground state leading, in the excited state, to a deep blue fluorescent emission through strong π–π intramolecular interactions between the two ‘aryl/fluorene/aryl’ arms. 2 has been successfully used as an emitting layer in a SMOLED with electroluminescence arising from electrogenerated intramolecular excimers and the properties of these excimer-based OLEDs have been compared to those of two model compounds (1 and 3). The simple and non-optimized double-layer device displays a deep blue colour (CIE coordinates: 0.19; 0.18) exhibiting a luminance of 510 Cd m−2 with a luminous efficiency of ca. 0.1 Cd A−1. This work is, to the best of our knowledge, the first rational and comparative study describing an intramolecular excimer based-SMOLED.

Dependence of the Properties of Dihydroindenofluorene Derivatives on Positional Isomerism: Influence of the Ring Bridging

The future of organic electronics is driven by the synthesis and the study of novel molecular fragments for the construction of highly efficient polymers or oligomers. In this context, polyand oligophenylene derivatives constitute an important class of highly promising molecules, which have been widely studied for the last two decades. Of particular interest in the chemistry and physics of oligophenylenes is the bridged-para-terphenyl unit, namely, 6,12dihydroindeno[1,2-b]fluorene (Scheme 1). Although it has been known since the 1950s, investigations of the dihydroindeno[1,2-b]fluorenyl core only started a decade ago thanks to the pioneering work of M llen, which made this molecule a key building block for electronics. There are nowadays numerous examples of efficient dihydroindeno[1,2-b]fluorenylbased semiconductors that have found application in various fields, such as fluorescent 5–8] and phosphorescent organic light-emitting diodes (OLEDs), organic field-effect transistors, and organic solar cells. This wide range of applications clearly shows the high potential of this building block, but also its versatility. However, the dihydroindeno[1,2-b]fluorene is not the only member of the bridged-terphenyl family, since it possesses four other positional isomers with different phenyl linkages (para/meta/ortho) and different ring-bridging positions (anti vs. syn ; Scheme 1). There are hence five dihydroindenofluorene positional isomers, each possessing its own ring topology, which in turn has structural and electronic consequences. However, in contrast to the dihydroindeno[1,2-b]fluorene, other positional isomers remain very scarce in the literature owing to synthetic difficulties. For example, the dihydroindeno[2,1-a]fluorenyl (syn para-terphenyl) unit (Scheme 1) has only been investigated for organic electronics very recently, and thanks its particular syn geometry has emerged as a promising scaffold for a new generation of excimer-based OLEDs. Similarly, antiaromatic fully conjugated indenofluorene derivatives have recently attracted particular attention; Haley and co-workers have for example reported a new class of (2,1-c)indenofluorenes with high electron affinities. However, the anti and syn meta-terphenyl isomers, that is, dihydroindeno[1,2-a]fluorene and dihydroindeno[2,1-b]fluorene, although known for 60 years, are almost absent from the literature, and their intrinsic properties have never been studied. As the design of novel molecular fragments is of key importance for the future of organic electronics, we report herein the first examples of the use of dihydroindeno[1,2b]fluorene (1) and dihydroindeno[2,1-a]fluorene (2 ; Scheme 1. The five positional dihydroindenofluorene isomers.

The anodic oxidation of fluorene and some of its derivatives: conditions for the formation of a new conducting polymer

Introduction (avant ou apres polymerisation) de groupes redox qui peuvent posseder des proprietes specifiques chimiques et electrochimiques

Tuning the optical properties of aryl-substituted dispirofluorene-indenofluorene isomers through intramolecular excimer formation.

Two families of positional isomers of dispirofluorene-indenofluorene substituted by phenyl groups at the 2,7-positions of the fluorene moieties present drastically different optical properties. The emission wavelengths may be gradually and conveniently modulated for one of the two isomers by the phenyl groups substituent whose bulkiness controls the extent of the excimeric interaction evidenced in this paper.

New Dispiro Compounds: Synthesis and Properties

We report the synthesis and structural characterization of two dispiro compounds. These two positional isomers have been designed and synthesized through an efficient method. Because of the rigidity and orthogonality of the spiro bridge, both molecules exhibit a well-defined architecture which consists of two fluorene rings connecting to an indenofluorenyl unit via two sp3 carbon atoms. The structural, electrochemical, optical, and thermal properties of these dispiro isomers are discussed.

9,9′-Spirobifluorene and 4-phenyl-9,9′-spirobifluorene: pure hydrocarbon small molecules as hosts for efficient green and blue PhOLEDs

We report herein a new pure hydrocarbon material, 4-phenyl-9,9′-spirobifluorene (4-Ph-SBF), with a high triplet energy level (ET: 2.77 eV) as a host for blue phosphorescent organic light-emitting diodes (PhOLEDs). Structural, thermal, electrochemical and photophysical properties have been investigated in detail and compared to its constituting building block 9,9′-spirobifluorene (SBF) in order to precisely study the influence of the incorporation of a phenyl unit in C4. A surprising out of plane deformation of the fluorene ring and a highly twisted structure have been notably found for 4-Ph-SBF due to the substitution in C4. As both 4-Ph-SBF and SBF possess a high triplet energy level (2.77/2.87 eV resp.), they have been successfully used as host materials for green and blue PhOLEDs. The performance of blue PhOLEDs, ca. 20 cd A−1, appears to be among the highest reported for pure hydrocarbon derivatives.

Encumbered DiSpiro[Fluorene–IndenoFluorene]: Mechanistic Insights

Research and advances in organic electronics have increased the demand for oligomers and polymers of controlled structure needed for applications as diverse as, for example, solar cells, light-emitting diodes, field-effect transistors or field-effect light-emitting transistors. Well characterized smaller molecular units, however, are more suitable than extended p-conjugated polymers for detailed structure–property relationships studies. In such molecular frameworks, the introduction of spiro linkages has interesting structural consequences and have been extensively developed, for instance, in the Tour and Salbeck groups. In our quest for efficient materials for organic light emitting diodes, we designed and studied molecules that combine two fluorene moieties to the indenofluorene core through a spiro-linkage (i.e., dispiro[fluorene-9,6’-indenoACHTUNGTRENNUNG[1,2-b]fluorene-12’,9’’-fluorene], DSF-IF; see R substituted type-2 molecules in Scheme 1). The synthetic approach involves, in the last step, the intramolecular bicyclization of the diol 1 (Scheme 1). Intramolecular electrophilic cyclization in the presence of a Lewis acid is a very common and useful reaction that has been widely used to generate a spiro configuration in mild conditions. For example, Yamagushi and coworkers have reported a double intramolecular cyclization reaction, which should in principle lead to the formation of two regioisomers, however, the authors reported the detection of only one isomer. Similarly, M llen and co-workers have reported the synthesis of poly(p-phenylene-alt-anthrylene) also using an intramolecular cyclization as the last step. Again, the reaction carried out on model compounds indicated that only the anti-ring-closed isomer is formed. We note, however, that indolocarbazole positional isomers with a conceptually related terphenyl backbone have been previously reported by Leclerc and co-workers. While extending the scope of type-2 molecules through the introduction of different R groups on the fluorene moieties (Table 1), we recently managed to separate and fully characterize two positional isomers of DSF-IF derivatives, namely

Anodic oxidation of 9,9'-spirobifluorene in CH2Cl2 + 0.2 M Bu4NBF4. Electrochemical behaviour of the derived oxidation product

The physicochemical properties and electrochemical behaviour of products obtained by anodic oxidation of 2-aminofluorene in CH2Cl2 + 0.2 M Bu4NBF4 are presented together with the oxidation conditions.