Cyril Poriel

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. To date, this is the highest performance ever reported for a blue PhOLED by using a dihydroindenofluorene derivative. Through this structure-property relationship study, a remarkable difference of performance between syn and anti isomers has also been highlighted. This surprising behaviour has been attributed to the different symmetry of the two molecules, and highlights the importance of the geometry profiles in the design of host materials for PhOLEDs.

The structure–property relationship study of electron-deficient dihydroindeno[2,1-b]fluorene derivatives for n-type organic field effect transistors

A bridged syn triphenylene derivative, namely 5,7-dihydroindeno[2,1-b]fluorene, functionalized with dicyanovinylene units (2,1-b)-IF(C(CN)2)2 has been designed, synthesized and characterized. Its optical and electrochemical properties have been carefully studied through a combined experimental and theoretical approach and compared to those of three other structurally related dihydro[2,1-b]indenofluorene derivatives bearing methylenes, (2,1-b)-IF, carbonyls, (2,1-b)-IF(O)2, or both carbonyl and dicyanovinylene, (2,1-b)-IF(O)(C(CN)2) on the bridgeheads. (2,1-b)-IF(C(CN)2)2, which possesses a very low LUMO level, ca. −3.81 eV, has been successfully used as an active layer in n-channel OFETs using an epoxy based photoresist SU-8 as the gate insulator. (2,1-b)-IF(C(CN)2)2 based n-channel OFETs show promising properties such as a low threshold voltage functioning of 7.2 V (low gate–source and drain–source voltages), a high ratio between the on and the off currents (6.3 × 105), interesting subthreshold swing (SS = 2.16) and electron mobility (>10−3 cm2 V−1 s−1) and excellent stability under electrical stress. This electrical stability has allowed the incorporation of (2,1-b)-IF(C(CN)2)2 based n-channel OFETs in an integrated circuit. Thus, as a proof of concept, pseudo CMOS inverters made of n-type (2,1-b)-IF(C(CN)2)2-based OFETs have been fabricated and characterized highlighting the potential of this new family of materials.

An electron deficient dicyanovinylene-ladder-type pentaphenylene derivative for n-type organic field effect transistors

A bridged pentaphenylene derivative functionalized with dicyanovinylene units LPP([double bond, length as m-dash]C(CN)2)2 has been designed, synthesized and characterized. The optical and electrochemical properties have been carefully studied through a combined experimental and theoretical approach and compared with those of two pentaphenylene derivatives bearing methylenes (LPP) or carbonyl (LPP([double bond, length as m-dash]O)2) on the bridgeheads. LPP([double bond, length as m-dash]C(CN)2)2 which possesses a very low LUMO level, ca. −4.02 eV, has been successfully used as an active layer in n-channel OFETs using the epoxy based photoresist SU-8 as a gate insulator. LPP([double bond, length as m-dash]C(CN)2)2 based n-channel OFETs show low voltage functioning (low gate-source and drain-source voltages), high ratio between the on and the off currents (2 × 105), interesting subthreshold swing (S = 1) and excellent stability under electrical stress and in a nitrogen atmosphere. More importantly, we have also shown that LPP([double bond, length as m-dash]C(CN)2)2 based n-channel OFETs present an excellent environmental stability. This work is to the best of our knowledge the first report on bridged pentaphenylene-based semiconductors in n-type OFETs and highlights the potential of such type of material to provide air stable OFETs.

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. The first member of a new family of spirobifluorenes substituted in the 1-position, which presents better performance 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.

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.

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. Dihydroindenofluorenes have also appeared as very promising building blocks for OE applications. In the dihydroindenofluorene family, there are five positional isomers, with three different phenyl linkages ( para/ meta/ ortho) and two different ring bridge arrangements ( anti/ syn). We have focused on the concept of positional isomerism. Indeed, the structural differences of the dihydroindenofluorenyl cores lead to unusual electronic properties, which our group has described since 2006, thanks to the five dispirofluorene-indenofluorene positional isomers (dihydroindenofluorenes substituted on the bridges by fluorenyl units). 6,12-Dihydroindeno[1,2- b]fluorene (the para-anti isomer) is constructed on a p-terphenyl core and possesses an anti geometry. Although this isomer has been widely investigated over the last 20 years, studies of the four other isomers remain very scarce. 11,12-Dihydroindeno[2,1- a]fluorene (the para-syn isomer) is also built on a bridged p-terphenyl core but possesses a syn geometry. This particular geometry has been advantageously used by our group to drastically tune the electronic properties, and this isomer has emerged as a promising scaffold to obtain stable blue emission arising from conformationally controllable intramolecular excimers. These preliminary studies have shown the crucial influence of the geometry on the electronic properties of the dihydroindenofluorenes. Modification of the arrangement of the phenyl linkages from para to meta provides the meta isomers, namely, 7,12-dihydroindeno[1,2- a]fluorene (the meta-anti isomer) and 5,7-dihydroindeno[2,1- b]fluorene (the meta-syn isomer). With these two regioisomers, the strong impacts of both the linkage and the geometry on the electronic properties have been particularly highlighted over the years. The last positional isomer of the family is 5,8-dihydroindeno[2,1- c]fluorene, which possesses a central o-terphenyl backbone and a syn geometry. This isomer is unique because of its ortho linkage, which induces a particular helicoidal turn of the dihydroindenofluorenyl core. Using a structure-property relationship approach, in the present Account we describe the molecular diversity of the five dispirofluorene-indenofluorene positional isomers and the consequences both in terms of their organic synthesis and electronic properties. This Account shows how positional isomerism can be a powerful tool to tune the electronic properties of OSCs.

Discrimination of positional isomers by ion mobility mass spectrometry: application to organic semiconductors

Organic semiconductors are increasingly being used in organic-based opto-electronic devices. Since regioselective synthetic approaches are not always controlled, promising compounds are sometimes prepared following non-regioselective routes. Ion mobility mass spectrometry is here introduced as a direct method to distinguish isomers in mixtures, instead of undertaking time-consuming analytical chromatography procedures.