Effects of vinylene and azomethine bridges on optical, theoretical electronic structure and electrical properties of new anthracene and carbazole based π-conjugated molecules

摘要

This study aims to synthesize and characterize a new semi-conducting 2,7-distyrylcarbazole-based molecule (M1) and its Schiff-base analog (M2). Those two molecules were synthesized via Wittig-Horner and diamine condensation reactions, respectively. The effects of replacing the vinylene (CHCH) linkage between carbazole donor unit and anthracene acceptor unit in moleculeM1by an azomethine (CHN) bridge in moleculeM2on physicochemical and electrical properties are reported in this work. Thermal characterization shows a semi-crystalline morphology in solid state for the two organic materials and a good thermal stability up to 370 °C in the case ofM2.The observed non-fluorescence character of the Schiff-base molecule has been related to the photo-induced electron transfer (PET) process from the imine receptor moiety to the anthracene fluorophore unit. The effect of the addition of trifluoroacetic acid (TFA) on optical properties of the Schiff base molecule revealed a significant blue shift of the absorption spectrum and a turn-on of the fluorescence as well as visual changes. Computational analyses by Density Functional Theory (DFT) and time-dependent (TD-DFT) were then used to obtain conformation and the energy distributions of the molecular orbitals of the two compounds. The electrochemical behaviors were investigated by cyclic voltammetry and showed a reduction of the band gap ofM2as compared toM1du to the electron-withdrawing effect the azomethine (–CHN–) bond. Finally, the charge-carrier mobility of the two compounds were extracted from single-layer diodes in the space-charge limited current regime (SCLC) and organic field effect transistors (OFETs) demonstrating lower hole mobilities in the case ofM2based thin film devices. The hole effective mobility ofM2(measured by SCLC) was one order of magnitude higher after exposition to trifluoricacetic acid vapors than in neutral films.