SYNTHESIS AND CHARACTERIZATION OF MATERIALS BASED ON INDOLOQUINOXALINE

Abstract

The aim of the research described in this thesis to explore the structure-property relationship of substituted indoloquinoxaline derivatives in an attempt to develop emitting functional materials. Indoloquinoxaline contains both indole and quinoxaline segments fused together and consequently considered as built-in dipolar entity. Such dipolar architecture may be fine tuned by appropriate substitution in one of the functional segments. Obviously in the present core the donor substituents on the indole unit or in an electronically communicating position to it will enhance the donating ability while the incorporation of electronwithdrawing substituents will reduce it. In this thesis a study on the alternations in the electro-optical properties of the derivatives resulting due to the introduction of electron releasing moieties such as arylamines or electron accepting fragments such as oxadiazole or quinoxaline is performed. The thesis is divided into eight chapters. First chapter briefs the aim and scope of the work and identifies the areas to be explored. A thorough survey of literature related to synthesis and electronic applications of quinoxaline based materials is presented in Chapter 2. Quinoxaline based materials in the context of their application in electronic devices may be classified as: (a) electron transporting and (b) dipolar dual functional materials. On the basis of their structure they are grouped as: (a) quinoxaline and (b) fused quinoxaline derivatives. Normally, quinoxalines due to their electron-accepting nature function as electrontransporting layer in organic light-emitting diodes. However, incorporation of electrondonating groups such as triarylamines renders hole-transporting ability. Quinoxalinetriarylamine conjugates were demonstrated as efficient electroluminescent materials. Aromatic segments fused with pyrazine or quinoxaline segment have been studied in detail iv due to their unique emission and thermal properties. Functionality of such fused quinoxalines is mainly decided by the nature of the fusing segment. For instance, the substituted pyrazoloquinoxalines and thienopyrazines have been demonstrated to possess excellent emission and balanced charge transport characteristics. From the literature survey, it is clearly evident that due to the structural simplicity and ease of formation from commercially cheap starting materials the quinoxaline based compounds have been abundantly used as functional materials for electro-optical and biological applications. Even though a wide variety of quinoxalines are known, a structure property relationship for indoloquinoxalines remains unexplored. Particularly we are interested in elucidating the changes in the electro-optical properties arising due to the variation in the nature of the substituents present in the indoloquinoxaline nucleus...............