DIPOLAR COMPOUNDS FOR ELECTRO-OPTICAL APPLICATIONS

Abstract

Recently, there is a growing interest for the development of dipolar compounds suitable for application in electro-optical devices such as organic light-emitting diodes (OLED), thin film transistors (TFT) and photovoltaics. Major attraction for the dipolar compounds arises due to their promising charge transport and optical properties. Consequently several donor, acceptor and linker groups have been explored in the construction of dipolar compounds with an aim to achieve optimized materials possessing efficient functional capabilities. For the organic light-emitting diodes, dipolar compounds featuring emission characteristics are required while for the dye-sensitized solar cells (DSSC) the dyes need to undergo charge separation at the excited state at the expense of the emission. In this dissertation, we explore the compounds derived from benzo[a]phenazine and amine functionalized fluorene as potential materials for dye-sensitized solar cells. Pyrazine and the fused pyrazines (quinoxaline) are considered as electron-accepting moieties and have been exploited for the construction of electron-transporting materials. Integration of electron-donating arylamines on the pyrazine or quinoxaline nucleus has led to an array of dipolar materials with balanced charge transport. Similarly, the fluorene based triarylamines and their derivatives have been extensively studied as components in the organic light-emitting diodes and photovoltaics. However, to the best of our knowledge the amine substituted benzo[a]phenazines and fluorene bridged organic dyes containing acetylene linkages or additional amine moieties are not reported in the literature. In this thesis we report the functional materials derived from the above mentioned cores. The thesis is divided into six chapters. First chapter presents the aim and scope of the work. The dipolar compounds are expected to benefit the performance of the corresponding devices by balancing the rates of injection and transportation of both electrons and holes. Second chapter outlines the review of the available literature related to the synthesis and electro-optical characterization of dipolar compounds. The strategies used for the synthesis of the dyes and their physical characterization techniques are presented in the third chapter. The characterization data ('H, 13C NMR, IR and mass spectroscopy) of the newly synthesized compounds are also compiled in this chapter. Chapter 4 describes the synthesis, photophysical, electrochemical and thermal characterization of the dipolar compounds based on benzo[a]phenazine core. This chapter is divided into two sections; one dealing with the amine containing benzo[a]phenazine emitters and the other describing the sensitizers suitable for application in dye-sensitized solar cells. The dyes were constructed by following a novel metal free C-N or C-C bond forming reactions of 1,2-naphthoquinone with the secondary amines. Both the dialkylamines and diarylamines participated in these reactions efficiently. The dialkylamines generally produced the C-N coupling product while the diarylamines depending on the reaction conditions and the nature of the diarylamine either formed C-N coupling product or the C-C coupling product. When the reactions were performed in an apolar solvent, chloroform, the C-N bond formation occurred, while a reaction conducted in a protic solvent, methanol, led to the formation of the C-C coupled product. However, irrespective of the solvent used in the reaction, carbazole yielded the C-Ncoupled product while the N-phenyl-1-naphthylamine produced the C-C coupled product. The amine substituted 1,2- naphthoquinones were then converted to the benzo[a]phenazines by treatment with 1,2-diaminobenzene in the presence ofp-toluenesulfonic acid ....................