Carbazole, Fluorene and Perylene Based Materials for Potential Applications in Organic Light Emitting Diodes-Syntheses and Characterization

conjugated molecules are integral components of organic light-emitting diodes (OLEDs) responsible for light creation via absorption and emission, charge transportation and recombination. The present thesis focuses on the syntheses, characterization and studies of conjugated polymeric and small molecules for potential applications in OLEDs and multifunctional materials addressing the carbazole, fluorene and perylene. Carbazole-based materials are thoroughly studied electro- and photoluminescent stuff with excellent stability; these are common in the field of organic electronics due to their hole-transporting properties. Thus, some new carbazole-based polymers were synthesized in good yields by a cost-effective, modified Chichibabin reaction. The methodology involved the alkylation of carbazolic nitrogen, followed by Friedel-Crafts acetylation at 3,6 positions to afford the monomer. Polymerization entailed reaction with suitably- substituted benzaldehydes using ammonium acetate in refluxing acetic acid leading to creation of pyridine ring in situ, thus, comprising both hole- and electron-transporting moieties in the unit. Different alkyl chains were attached to investigate the effect of chain length on thermal properties. Similarly, the influence of electron-donating and electron- withdrawing substituents on the optical properties was also studied. Polymers exhibit good thermal stability, good solubility with blue emission. A second series of polymers having octyl chain and 3,3'-biscarbazolyl moiety was synthesized using the same methodology, exploiting better thermal properties of biscarbazole unit. The resulting polymers possess improved thermal stability, blue emission with solution processability providing the potential use as charge-transporting as well as light-emitting materials in OLEDs. In addition to the polymeric materials, different small molecular entities employing carbazole/fluorene core were also synthesized by Suzuki cross coupling in good yields. Fluorene was preferred due to its excellent morphological stability and blue light emission. A variation of the core nucleus from fluorene to carbazole was a key point to study its effect on thermal, optical and electrochemical properties. All molecular substances exhibited high thermal stability and blue emission. Perylene is a well-known n-type stable material. Different small molecular frameworks having the substitution on imide part and the bay position of the perylene nucleus were also synthesized. The synthetic strategy aimed at the imidization with suitable anilines followed by nucleophilic substitution with phenols. The resulting objects are amorphous in nature, possess good solution processability and electron-transporting properties due to their decreased LUMO level with good emissive properties ranging from yellow to orange depending on the substituents, thereby indicating their potential use in OLEDs as either electron-transporting or emissive layers. All the synthesized compounds were characterized by spectroscopic techniques like FTIR, 1H-NMR, 13C-NMR, mass spectrometry and the elemental analyses.