Since the breakthrough by Kodak in 1987, organic light-emitting diodes (OLEDs) have been seen as one of the most promising technologies for future displays. A number of materials have been developed and improved in order to fulfil the requirements of this application. The materials differ from one another by their structure but also by the mechanism involved in the electroluminescence produced (fluorescence versus phosphorescence). When properly stacked, these materials result in a device that can achieve the required high efficiency and long lifetime. Such red, green and blue devices can then be combined in matrices to become the core of a display. Building up these structures onto a display backplane is one of the challenges facing the industry. The circuitry for driving the pixels can be adapted to the OLED, sometimes at the expense of the simplicity of the display, but bearing in mind that the fabrication process must remain industrially viable.

Hybrid perovskites have emerged over the past five years as absorber layers for novel high-efficiency low-cost solar cells combining the advantages of organic and inorganic semiconductors. Unfortunately, electrical transport in these materials is still poorly understood. Employing the linear response approach of density functional theory, we reveal strong anharmonic effects and a double-well phonon instability at the center of the Brillouin zone for both cubic and orthorhombic phases of inorganic CsPbI. Previously reported soft phonon modes are stabilized at the actual lower-symmetry equilibrium structure, which occurs in a very flat energy landscape, highlighting the strong competition between the different phases of CsPbI. Factoring these low-energy phonons into electron-phonon interactions and band gap calculations could help better understand the electrical transport properties in these materials. Furthermore, the perovskite oscillations through the corresponding energy barrier could explain the underlying ferroelectricity and the dynamical Rashba effect predicted in halide perovskites for photovoltaics.

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.

This work reports the use of 9,9′-spirobifluorene and 4-phenyl-9,9′-spirobifluorene, pure hydrocarbon small molecules, as hosts for efficient green and blue phosphorescent OLEDs.

Abstract:The present works report the first structure-properties relationship study of a key class of organics semiconductors, ie 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 rationalized. 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. The first member of a new family of spirobifluorenes substituted in position 1, which presents better performances in blue Phosphorescent OLEDs than those of its regioisomers is reported. These features highlight not only the great potential of 1-substituted spirobifluorenes but also the remarkable impact of regioisomerism on electronic properties.

This work describes the first thermally activated delayed fluorescence material enabling circularly polarized light emission through chiral perturbation. These new molecular architectures obtained through a scalable one-pot sequential synthetic procedure at room temperature (83% yield) display high quantum yield (up to 74%) and circularly polarized luminescence with an absolute luminescence dissymmetry factor, |glum|, of 1.3 × 10−3. These chiral molecules have been used as an emissive dopant in an organic light emitting diode exhibiting external quantum efficiency as high as 9.1%.

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. [1] In this context, poly-and oligophenylene derivatives constitute an important class of highly promising molecules, which have been widely studied for the last two decades. [2,3] 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, [4] investigations of the dihydroindeno[1,2-b]fluorenyl core only started a decade ago thanks to the pioneering work of Müllen, which made this molecule a key building block for electronics. [2] There are nowadays numerous examples of efficient dihydroindeno[1,2-b]fluorenylbased semiconductors that have found application in various fields, such as fluorescent [2,3,[5][6][7][8] and phosphorescent [9] organic light-emitting diodes (OLEDs), organic field-effect transistors, [10][11][12] and organic solar cells. [13] 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, [14] and thanks its particular syn geometry has emerged as a promising scaffold for a new generation of excimer-based OLEDs. [15] Similarly, antiaromatic fully conjugated indenofluorene derivatives have recently attracted particular attention; [16][17][18][19] Haley and co-workers have for example reported a new class of (2,1-c)indenofluorenes with high electron affinities. [20] 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, [21] are almost absent from the literature, [22] 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.

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