Synthesis and Characterizations of Linear and Ladder Conjugated Polymers

Abstract

Semiconducting polymers have gained tremendous attention in the past decades as a potential alternative over Si-based semiconductors. The research on tuning the band gap of semiconducting polymers has mainly focused on the development of new electron donor and acceptor building blocks. Post-polymerization such as annulations and modification of functional groups is considered as an effective approach to the band-gap tuning for semiconducting polymers. The first part of this thesis describes the synthesis and characterization of ladder and linear-ladder polymers by post-polymerization annulations. 8-Octylnaphtho[2,3-c]thiophene-4,9-dione (NTDO) having the two keto groups was incorporated into conjugated linear polymers, which were then treated with Lawesson's Reagent (LR) for post-polymerization annulation. The obtained ladder and linear-ladder polymers had a lower energy band gap and absorption at a longer wavelength in comparison with their precursor polymers. The linear-ladder polymers containing of the electron-donating thiophene units and electron-withdrawing benzothiadiazole units had the absorption onset in the NIR region, e.g., at 1300 nm and 1000 nm, respectively. The second part discusses chemical transformations of the NTDO-containing conjugated polymers. The transformation by sequential reduction, dehydration, and esterification on the NTDO homopolymer was successful. The energy band gap decreased, absorption maxima were red-shifted and the absorption spectrum was broadened after chemical transformation. The transformation of the keto group of NTDO-based D-A polymers to the corresponding dicyanovinylene group unexpectedly resulted in an increase of the LUMO energy level and therefore an increase in energy band gap. In the third part of this thesis, the building block of thieno[3,4-c]pyrrole-4,6-dione (TPD) was incorporated into conjugated linear polymers. Treatment of TPD-containing polymers with LR led to conversion of the keto group to thio-keto instead of annulation by intramolecular coupling. The obtained polymer displayed a hypsochromic shift and a higher energy band gap. In the final part of this thesis, fluorene-based conjugated polymers containing the AIE-active tetraphenylethene and dicarboxylate pseudocrown as an ion receptor were synthesized and the optical sensing for lead ion was investigated. The study showed that polymer structure, solvent polarity, and nature of probe-analyte complex play collective roles in the dual-mode fluorescence detection for lead ion.