Synthesis and photo-physical properties of carbazole and benzimidazole based fluorescent derivatives (PhD)

Abstract

Fluorescence is a fast, simple and inexpensive method to determine the concentration of an analyte in solution. Fluorescent chemosensors have been reported for sensing of biologically important species such as metal ions, anions and small molecules. These chemosensors measure the change in the photo-physical properties of the system to report the presence of an analyte. The presence of an analyte can be detected via quenching or enhancement of fluorescence signal. The organic molecules emitting fluorescence are known as fluorophores. We chose carbazole and benzimidazole as fluorophore for the chemosensing as carbazole has a strong 𝜋 electron conjugation and high thermal stability. It’s optical and electrical properties can be easily tuned by putting various substituents at different positions. Carbazole based molecules are widely used in various areas such OLEDs, nanoparticle formation, sensing of cations, anion, and molecules.Similarly, Benzimidazole is a heterocyclic molecule incorporating an imidazole and benzene ring. Because of their emissive properties benzimidazole derivatives have been commonly used as probe for recognition of all cations, anions and neutral molecules. Benzimidazole based molecules possess distinctive linear and non-linear optical properties and have an outstanding thermal stability in guest–host systems. Benzimidazole derivatives have also an important role as pharmacophore in medicinal chemistry. The key feature of chemosensors is to detect analytes like cations, anions and small molecules and consecutively induce a recognition–transduction signal. The development of chemosensors occurs by the combination of mainly two units i.e. the binding site and the signaling subunit. Functionalization of chemosensors enables it to undergo various binding phenomenon which can be detected with different signaling mechanisms viz. PET, ICT, TICT, Excimer, ESIPT, FRET, AIEE in fluorescence spectroscopy. Recently, aggregation induced emission enhancement (AIEE) materials have been used for fluorescent detection of environmentally and biologically significant ions and molecules. AIEE is an unusual phenomenon in which organic luminophores show higher luminescence in the aggregated state than in solution. The AIEE phenomenon basically works on the synergistic effect of restricted intramolecular rotation (RIR) and twisted molecular conformation. In the present thesis, we designed and synthesized new fluorescent carbazole based derivatives exhibiting phenomenon of aggregation induced emission enhancement (AIEE). We have also synthesized benzimidazole based derivatives exhibiting phenomenon of twisted state intramolecular charge transfer (TICT) and sensing analyte through chemosdosimetry approach. The work is distributed in six different chapters from chapter 2 to chapter 7 excluding chapter 1 and chapter 8 which includes introduction and conclusion respectively.