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.

Simplifying the structure of Organic Light-Emitting Diodes (OLEDs) has been for the last twenty years the purpose of many studies. However, despite these efforts, only a few materials provide high...

In this work, we propose pure hydrocarbon materials as universal hosts for high-efficiency red, green and blue phosphorescent organic light-emitting diodes.

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. Three [4]cyclo-N-alkyl-2,7-carbazoles bearing different alkyl chains on their nitrogen atoms have been synthesized and characterized by combined experimental and theoretical approaches. This study includes electrochemical, photophysical, thermal and structural solid-state measurements and charge transport properties investigations. An optimized protocol of the Pt approach has been developed to synthesize the [4]-cyclocarbazoles in high yield (52-64%), of great interest for further development of nanorings especially in materials science. The charge transport properties of [4]-cyclocarbazoles and a model compound, [8]-cycloparaphenylene ([8]CPP), have been studied. Although no field effect (FE) mobility was recorded for benchmark [8]CPP, FE mobility values of ca 10 -5 cm².V -1 .s -1 were recorded for the [4]-cyclocarbazoles. The characteristics (threshold voltage VTH, subthreshold swing SS, trapping energy ∆E) recorded for the three[4]-cyclocarbazoles appear to be modulated by the alkyl chain length borne by the nitrogen atoms. Remarkably, the space-charge-limited current mobilities measured for the [4]-cyclocarbazoles are about 3 orders of magnitude higher than that of [8]CPP (1.37/ 2.78×10 -4 for the [4]-cyclocarbazoles vs 1.21×10 -7 cm².V -1 .s -1 for [8]CPP) highlighting the strong effect of nitrogen bridges on the charge transport properties. The whole study opens the way to the use of nanorings in electronics, which is now the next step of their developments.

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. The optical properties were characterized both in solution and thin film by UV/visible spectroscopy as well as stationary and time‐resolved fluorescence. It was found that this [4]cyclofluorene displays different characteristics compared with the other [4]cyclofluorenes substituted by methyl or propyl chains: a simple modification of the chain length induces a non‐negligible effect on the emission properties, which must be linked to the specific arrangement of the fluorene units. Furthermore, single‐crystal X‐ray diffraction reveals the formation of a pseudo‐tubular solid‐state arrangement of fully symmetrical ring structures, which was not observed for the other members of the [4]cyclofluorenes family. This finding could open the way to modulation of properties of cyclofluorenes through alkyl chain engineering.

Solvent polarity effect on circularly polarized luminescence intensity was assessed in helical push–pull organic systems through excited-state symmetry breaking and interbranched exciton coupling.

Diodes with high performance either for the green (EQE of 20.2%) or the blue colour (EQE of 9.6%). These performances are, to the best of our knowledge, among the highest reported to date for 4-substituted SBF derivatives.

Spirobifluorene (SBF) is one of the most important scaffolds used in the design of organic semi‐conductors (OSCs) for electronics. In recent years, among all the structures developed for these applications, SBF dimers have been highlighted due to their great potential in thermally activated delayed fluorescence and in phosphorescent organic light‐emitting diodes. Attaching two SBF units generate 10 dimers, each possessing its own structural specificity, which in turn drives its electronic properties. These ten SBF dimers are gathered herein. Understanding how the molecular assembly determines the electronic properties has been one of the pillars of organic electronics. This is the goal of this article. As positional isomerism is a key tool to design OSCs, defining the design guidelines for the SBF scaffold appears of interest for the future of this building block. Herein, the importance of the two main parameters involved in the electrochemical and photophysical properties, namely the nature of the phenyl linkages and the steric congestion between the two SBF units is discussed. The combination of these two parameters drives the electronic properties but their respective weight is different as a function of the regioisomer involved or of the property considered (frontier orbitals energy level, absorption, fluorescence, phosphorescence).