Isomeric carbazolocarbazoles: Synthesis, characterization and comparative study in Organic Field Effect Transistors

We report here the synthesis and characterization of a new family of isomeric carbazolocarbazole derivatives, namely carbazolo[1,2-a]carbazole, carbazolo[3,2-b]carbazole and carbazolo[4,3-c]carbazole. Thermal, optical, electrochemical, morphological and semiconducting properties have been studied to understand the influence of geometrical isomerism on the optoelectronic properties of these compounds. Different packing patterns have been observed by single crystal X-ray diffraction (XRD) which then correlate with the different morphologies of the evaporated thin films studied by XRD and Atomic Force Microscopy (AFM). The effect of N-substituents has also been evaluated for one of the isomers revealing a noticeable influence on the performance as organic semiconductors in Organic Field Effect Transistors (OFETs). A good p-channel field effect has been determined for N,N′-dioctylcarbazolo[4,3-c]carbazole with a mobility of 0.02 cm² V^-1 s^-1 and I _on/I_off ratio of 10⁶ in air. These preliminary results demonstrate the promising properties of molecular carbazolocarbazole systems which should be further explored in the area of organic semiconducting materials.