Synthesis and Electropolymerization of π-Conjugated Donor-Acceptor Small Molecules and Their Optoelectronic Properties

Kumar, Chandan (2024) Synthesis and Electropolymerization of π-Conjugated Donor-Acceptor Small Molecules and Their Optoelectronic Properties. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Chandan Kumar (14IP040)) 14IP040.pdf - Submitted Version Restricted to Repository staff only Download (8MB)

Abstract

This thesis deals with the synthesis of BF2 formazanate complexes with thiophene and 3,4-ethylenedioxythiophene (EDOT) and their π-conjugated polymers in the form of electroactive uniform thin films by electrochemical polymerization. These new formazanates and their polymers possess panchromatic absorption with low-lying frontier molecular orbitals. With small band gaps (1.5-1.8 eV). these materials are good candidates for organic electronics and light-harvesting applications. A computational study on the charge transport properties of BF2 formazanates with 3,4-ethylenedioxythiophene (EDOT) indicated an ambipolar semiconductor nature. In one series, thiophene and 3,4-ethylenedioxythiophene (EDOT) were used as the donor units, and the BF2 formazanate core moiety was used as the acceptor. This is the first example of the electropolymerization of monomers with BF2 formazanate complexes in their backbone. These new formazanates and their polymers possess panchromatic absorption with low-lying frontier molecular orbitals. New indigo derivatives were synthesized and used as active layers in organic thin film transistors (OTFTs). The synthesized molecules are insoluble in common organic solvents; hence, modification is performed by introducing thermocleavable tert-butoxycarbonyl (Boc) groups. The presence of bulky Boc groups increased its solubility. Postdepositional thermal treatment at temperatures above 150°C could remove the Boc groups to restore the highly coplanar geometry of the unsubstituted indigo units. The studied pigments show strong p-type behavior, with n-type transport being nonobservable even in configurations promoting electron injection (Al source and drain). Pigment shows slight ambipolar behavior, with p-type behavior being an order of magnitude stronger (~10⁻² vs. ~10⁻³ cm²×V⁻¹×s⁻¹ hole and electron mobility, respectively). We reported the synthesis of polycyclic heteroaromatic compounds via DDQ-mediated C-C coupling under Scholl oxidation conditions. The active α,α-position of the thiophene ring couples together instead of the β position of the thiophene and the core part of the anthracene benzene ring. This molecule is composed of four fused thiophenes and two embedded cyclopentadiene rings along with an anthraquinone core. From the X-ray structure, we confirmed the saddle shape of the compound. We calculate the hole mobility (μh) by the space charge limited current (SCLC).

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