Synthesis of novel multifunctional carbazole-based molecules and their thermal, electrochemical and optical properties

Abstract

Two novel carbazole-based compounds <b>7a</b> and <b>7b</b> were synthesised as potential candidates for application in organic electronics. The materials were fully characterised by NMR spectroscopy, mass spectrometry, FTIR, thermogravimetric analysis, differential scanning calorimetry, cyclic voltammetry, and absorption and emission spectroscopy. Compounds <b>7a</b> and <b>7b</b>, both of which were amorphous solids, were stable up to 291 °C and 307 °C, respectively. Compounds <b>7a</b> and <b>7b</b> show three distinctive absorption bands: high and mid energy bands due to locally excited (LE) transitions and low energy bands due to intramolecular charge transfer (ICT) transitions. In dichloromethane solutions compounds <b>7a</b> and <b>7b</b> gave emission maxima at 561 nm and 482 nm with quantum efficiencies of 5.4% and 97.4% ± 10%, respectively. At positive potential, compounds <b>7a</b> and <b>7b</b> gave two different oxidation peaks, respectively: quasi-reversible at 0.55 V and 0.71 V, and reversible at 0.84 V and 0.99 V. At negative potentials, compounds <b>7a</b> and <b>7b</b> only exhibited an irreversible reduction peak at -1.86 V and -1.93 V, respectively.