Synthesis and properties of novel polycyclic (Hetero)aromatic systems

Abstract

Polycyclic aromatic hydrocarbons are ubiquitous functional molecules that have numerous applications in optoelectronic devices, molecular recognition and sensing, dye materials. Therefore, various synthetic organic chemistry and material research groups have devoted a significant effort towards these structural scaffolds. In this context, we describe the synthesis and properties of novel polycyclic (hetero)aromatic systems. Part 1 of the thesis begins with Chapter 1, which describes the synthesis and properties of phosphole-embedded polycyclic aromatic compounds (PACs). Chapter 2 describes the synthesis and properties of phospha[5]helicenes bearing an inner-rim phosphorus center. The key intermediate, 7-hydroxybenzo[b]phosphole oxide, was prepared in a regioselective manner from 3-(methoxymethoxy)phenylzinc reagent, 5-decyne, and PPhCl2 in a one-pot protocol. By utilizing the hydroxyl group as a synthetic handle, allowing the construction of the angularly fused carbohelicene moiety bearing an inner-rim phosphorus center in a concise manner. Based on 1H NMR and single crystal analysis, the thus-synthesized phospha[5]helicenes were demonstrated to undergo facile helicity inversion in solution, which was also corroborated by DFT calculations. Chapter 3 discusses about the synthesis and optical properties of phosphole oxide-fused triphenylene derivatives. As was the case of phospha[5]helicenes synthesis, 7-hydroxybenzo[b]phoshole oxide was utilized as a key precursor for the extension of the π-conjugation system, and the triphenylene core was furnished through dehydrogenative C-C coupling of biaryl (Scholl reaction). The present compounds represent rare examples of phosphole-embedded triphenylenes. The thus-synthesized compounds displayed strong blue fluorescence.

Part 2, Chapter 4 of the thesis, firstly describes a brief review on synthesis and properties of heptagon-embedded polyaromatic hydrocarbons and transition metal-catalyzed annulation reactions between alkynes and aromatic substrates. Secondly, this chapter describes the palladium-catalyzed annulation of 1-halo-8-arylnapthalenes and alkynes leading to heptagon-embedded aromatic systems with all sp2 carbon center. The reaction is promoted by the catalytic system comprised of Pd(OAc)2, moderate electron-deficient triarylphosphine P(4-ClC6H4)3 and Ag2CO3. Notable feature of the reaction is the broad substrate scope and variety of aryl groups on the 7- and 8-positions of the benzo[4,5]cyclohepta[1,2,3-de]naphthalenes and two-fold annulated heptagon containing PAHs.