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Abstract

This thesis focuses on the synthesis and characterization of azaacenes and stable azaacene radical cations.

In Chapter 2, the synthesis, properties, and solid state X-ray single crystal structures of two new rubrene derivatives, viz diazarubrene DAR and tetraazarubrene TAR, are reported. Both the azarubrenes are more oxidatively stable than rubrene itself and show similar optical properties but differ in their crystal packing from that of rubrene.

In Chapter 3, the synthesis, property evaluation, and single crystal X-ray structures of 5,7,12,14-tetrafunctionalized diazapentacenes (TDAPs) are presented. Starting from tetrabromo-N,N’-dihydrodiazapentacene, Pd-catalyzed coupling gave the precursors that furnished, after further redox reactions, the diazapentacenes as stable crystalline materials. The performance of the tetraphenylated compound as n-channel semiconductor was evaluated in organic field-effect transistors. In Chapter 4, a series of quinoidal N,N’-diaryl-N,N’-dihydrodiazapentacenes (Quinos) were prepared in a two-step reaction, starting from quinacridone. Oxidation of Quinos furnished stable radical cations, isoelectronic to the radical anions of the azaacenes, whereas the dicationic species are isoelectronic to neutral azapentacenes. The spectroscopic properties of the diaryldiazapentacenes and their oxidized mono- and dications are equivalent to that of the dianion of tetraazapentacene TAP, its radical anion, and the neutral TAP.

In Chapter 5, three stable N,N’-diarylated dihydroazaacene radical cations (DDAs+·) were prepared by oxidation of neutral N,N’-diarylated dihydroazaacenes (DDAs), synthesized through Buchwald-Hartwig aminations of aryl iodides with N,N’-dihydroazaacenes employing a palladium catalyst. The spectroscopic properties, single crystal X-ray structures, and DFT calculations of these neutral compounds and their radical ions were systematically investigated. All the radical cations are stable and their absorption spectra in dichloromethane remained unchanged in ambient conditions for at least 24 hours.