A Carbazole-based Fluorescent Turn-off Chemosensor for Iron (II/III) Detection in a Dimethyl Sulfoxide.

We designed a novel carbazole-based chemosensor from 2-(N-hexylcarbazol-3'-yl)-pyridine-5-carbaldehyde which was named probe 7b. The main purpose of this study is to investigate whether metal ions in liquid media can be detected with probe 7b. The details were presented in this paper. First, the molecular absorption and fluorescence properties of probe 7b were characterized by spectrophotometers. Then, several methods were applied to check its sensing properties. The results showed that probe 7b has a sense towards Fe3+ ion than other interfering metal ions. The selectivity and sensitivity of probe 7b towards Fe3+ were very satisfactory to use in applications. Also, it was observed that when aqueous Fe3+ ion solutions were added to probe 7b in dimethyl sulfoxide (DMSO), the fluorescence intensity of probe 7b decreased. This situation (turn-off of emission) is due to the paramagnetic effect between probe 7b and Fe3+ ions. The limit of detection (LOD) value was found as 1.38 nM for probe 7b. This value is very small to compete with its counterparts in the literature. A real sample experiment indicated that probe 7b can detect Fe3+ ions more than other ions in real media, too. As a result, it was deduced that probe 7b is a very strong candidate to use in sensor technology.

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

Two novel carbazole-based compounds 7a and 7b 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 7a and 7b, both of which were amorphous solids, were stable up to 291 °C and 307 °C, respectively. Compounds 7a and 7b 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 7a and 7b gave emission maxima at 561 nm and 482 nm with quantum efficiencies of 5.4% and 97.4% ± 10%, respectively. At positive potential, compounds 7a and 7b 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 7a and 7b only exhibited an irreversible reduction peak at -1.86 V and -1.93 V, respectively.