Structure properties relationship study of electron-deficient dihydroindeno [2,1-b]fluorene derivatives for n-type Organic Field Effect Transistors

International audience; A bridged syn triphenylene deriv., 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 electrochem. properties have been carefully studied through a combined exptl. and theor. approach and compared to those of three other structurally related dihydro[2,1-b]indenofluorene derivs. 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 (\textgreater10-3 cm2 V-1 s-1) and excellent stability under elec. stress. This elec. 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.