SYNTHESIS AND CHARACTERIZATION OF POLYAROMATIC HYDROCARBON-BASED FUNCTIONAL MATERIALS

Abstract

Polycyclic aromatic hydrocarbons (PAHs) such as anthracene, fluorene, pyrene, perylene, triphenylene, fluoranthene, benzo[&]fluoranthene, pentacene, and their derivatives have received immense attention as building blocks for materials suitable for application in optoelectronics due to their unique properties. They exhibit high thermal stability, good charge transporting characteristics and excellent emission properties owing to the structural rigidity and extended 7t-conjugation. Polymers, dendrimers, oligomers and monomers of PAHs have been reported as functional materials for organic light emitting diodes (OLEDs), photovoltaics including dye sensitized solar cells (DSSC) and thin-film transistors and as nonlinear optical materials (NLO) and optical sensors. PAHs when used as a 7r-linker in the construction of organic dyes suitable for dye-sensitized solar cells, they effectively assist the charge migration from the donor segment to the acceptor unit. PAHs may also be used as a building block in the triarylamine donor unit which generally helps to modulate the oxidation and dye regeneration propensities. Despite all these advantages, planar PAHs suffer from molecular aggregation which leads to unexpected emission and charge transport characteristics. However, this problem has been often circumvented by introduction bulkier nonplanar groups such as triarylamines or tert-butyl groups. Introduction of arylamines on PAHs backbone not only enhances the absorption and emission profiles but also increases the thermal stability, charge transporting ability and amorphous nature. In this thesis, we have explored the utility of PAHs such as fluoranthene, triphenylene and pyrene in the construction of organic dyes suitable for application in organic lightemitting diodes and dye-sensitized solar cells. We have used these cores as carriers for the functional groups such as arylamines and cyanoacrylic acid segment and studied the effect of the functional group introduction on the optical, electrochemical and thermal properties. The materials can be classified as emitting materials and dyes suitable for DSSC. We have also explored the application of selected compounds in OLED and DSSC. The thesis contains six chapters. In the first chapter, a review of the literature related to the work of the thesis has been presented. An up-to-date survey of the organic materials developed using PAHs as building block, have been performed. The optical, electrochemical and thermal properties of the known compound were compiled in the form of tables and an attempt to correlate the structure with the properties made. Generally, the PAHs due to their rigidity show enhanced thermal stability and the extended conjugation present in PAHs helps to realize a red-shifted emission. From the literature present in this chapter, it is abundantly i evident that PAHs have not been exploited for applications in electro-optical devices to the fuller extent mainly due to the lack of facile synthetic methodologies and their aggregation characteristics. Though n-n interactions present in aggregated species are beneficial for charge transport, aggregation is detrimental for emission properties. Thus, the molecular materials presented in this thesis were designed with an aim to inhibit the aggregation while exhibiting extended conjugation..............