Two isomers of azulene and indacenodithiophene (IDT)-based compounds 1 and 2 were designed and synthesized, according to the different connections of azulene unit with IDT through its electron-rich five-membered ring and the electron-deficient seven-membered ring, respectively. The UV-Vis spectra, electrochemical properties and proton-responsive properties of 1 and 2 were studied. Compounds 1 and 2 show obviously different physicochemical properties and device performance of organic field-effect transistors (OFET). Both compounds 1 and 2 have reversible proton response characteristics. The end absorption peaks of these two compounds are between 400 and 600 nm before protonation. With the addition of trifluoroacetic acid (TFA), the absorption peaks are red shifted to 550~850 nm. When they are protonated fully (TFA volume ratio is about 1%), they are red shifted about 200 and 177 nm, respectively. The color of compounds 1 and 2 in dichloromethane solution before protonation is red after the adequate protonation. It turned to blue and returned to its original color after the addition of triethylamine. OFET thin film devices of 1 and 2 showed an order of magnitude difference, with hole mobilities of 4.14×10^-3 and 1.05×10^-5 cm²·V^-1·s^-1, respectively. The different connections of IDT and azulene units through the electronic rich five-membered ring and the electronic deficient seven-membered ring of azulene greatly affect the materials’ device performance as well as their physicochemical properties, providing valuable insights for developing azulene-based novel organic functional molecules.

Key words: azulene, indacenodithiophene, isomer, organic field effect transistors