Small Molecule Organic Semiconductors: Syntheses, Strategies and Applications

Das, Sarasija (2022) Small Molecule Organic Semiconductors: Syntheses, Strategies and Applications. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Sarasija Das (13IP021)) 13IP021_DCS.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

This thesis deals with syntheses, strategies and applications of small molecule organic semiconductors, namely azaheterocycle, azapentacene and triphenylene derivatives. We have reported synthesis, characterization and application of an azaheterocycle obtained via FeCl3 mediated unconventional C-N coupling. The neutral azaheterocycle undergoes one-electron reduction to form an air-stable radical anion in situ, which provides added benefit towards operational stability of the device during n-type charge transport. The unusual stability of this radical anion is due to the fact that the fused cyclopentane ring upon reduction forms aromatic cyclopentadienyl anion, and the negative charge delocalizes over the nearly planar azaheterocycle core. The present azaheterocycle can be considered as a mimic of a fullerene fragment, which shows balanced ambipolar charge transport in space charge limited current (SCLC) devices with moderate hole (μh) and electron (μe) mobilities. Next, we have reported synthesis, characterization, and application of a stable 4nπ dihydrotetraazapentacene derivative. The neutral dihydrotetraazapentacene contains a 24π conjugated N-heteroacene core with two phenyl pendants appended thereof. The exceptional stability of this formally antiaromatic π-system is attributed to the fused dihydropyrazine ring which has two ethenamine (enamine) conjugations, and hence the π-electrons delocalize over the nearly planar azapentacene core to endow with global aromatic character. The embedded dihydropyrazine also offers an additional Clar’s sextet with enhanced aromaticity. The present dihydrotetraazapentacene can be considered as a multitasking N-heteroacene, which showed photoresponsive nature under visible light illumination, acidochromism in solution, and p-type charge transport with appreciable hole mobility in space charge limited current (SCLC) device. Finally, we have reported DDQ mediated solvent-free synthesis of 2,6,11-trimethyltriphenylene. We have also synthesized a new star-shaped triphenylene derivative equipped with three triphenylamine groups and explored its hole-transporting ability by means of the space charge limited current (SCLC) method.

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