Synthesis of heteroatom containing aromatic conjugated polymers using Acyclic Diene Metathesis (ADMET)

This doctoral thesis describes the synthesis of heteroatom (B/Si/Ge/Sn) containing conjugated macromolecules via Acyclic Diene Metathesis (ADMET) polycondensation. The main objective was to obtain a library of macromolecules with unique optical properties based on different aromatic segments and heteroatoms.;In chapter 2, the selective synthesis and characterization of a germanium containing macrocycle with two stilbene fluorophores is reported. The structure and size of the macrocycle were determined by 1H NMR, 13C NMR, GPC (polystyrene standards) and MALDI – TOF. The macrocycle features "all – trans" configuration at the vinylene bonds. The optical properties were studied by UV/Vis and fluorescence spectroscopy. The material emits in the blue region around 363 nm with a quantum efficiency of 0.4 relative to trans – stilbene. Theoretical calculations using B3LYP/6-31G** and Lanl2dz basis sets offered a better understanding of structural and electrooptical properties. They showed the presence of two important transitions in the absorption and the involvement of germanium orbital in the electronic conjugation with the stilbene segments.;Chapter 3 outlines the extension of this aforementioned synthetic strategy to the group 14 element boron, in order to generate a new class of conjugated macromolecules – homopolymers based on boron (p2a, p2b) and co-polymers based on silicon and boron (p12a, p12b). The structures and these new systems were determined by 1H NMR, 13C NMR and correlation NMR spectroscopy. The molecular weights were determined by GPC using polystyrene standards. Both the homopolymers and copolymers have "all – trans" configuration around the internal vinylene bonds. The copolymers were found to be random. The optical properties showed that all the macromolecules absorbed in the range of 327 – 406 nm and emitted at 416 nm (p2a, p12a) and 494 nm (p12b). The quantum efficiencies of these macromolecules were in the range of 0.28 – 0.30. p12a was found to be a potential fluoride ion sensor with very high sensitivity due to a polymer co-operative effect. Two distinct emissions dominated the emission spectrum of p12b, investigation of which indicated possible intermolecular energy transfer. The thermal properties indicated higher stability of the copolymers compared to the homopolymers. Degradation of p12a followed a two-step process and p12b was found to be more stable than p12a..;Chapter 4 of this thesis reports the synthesis of a library of homologous polymers based on Si, Ge, or Sn alternating with dithienylthiophene segments. The microstructures were analyzed by 1H NMR, 13C NMR and Correlation spectroscopy (HSQC, COSY). All the polymers p3a – c showed "all – trans" configuration at the vinylene bonds. The molecular weights were determined by GPC using polystyrene standards. No significant side products were observed under the ADMET conditions employed. Optical property analysis showed that the monomers were non-emissive whereas they absorb in the range of 263 – 264 nm. The polymers were highly fluorescent emitting in the range of 419 – 423nm. The quantum efficiencies were found to decrease from 0.18 to 0.11 from Si over Ge to Sn along with a small gradual blue shift of the emission maximum with the increase in size of the heteroatom. Thermogravimetric analysis indicated that Si based p3a showed the highest stability among the three homologous polymers.;Chapter 5 is strongly related and involves alkyloxy homologous side – chain substituted systems. The microstructures of the macromolecular products were analyzed by 1H NMR, 13C NMR showing that these polymers also have an "all – trans" configuration around the vinylene bond. The molecular weights were determined by GPC using polystyrene standards. Alkyloxy substituted silicon containing stilbene polymers showed a strong red shift compared to their stilbene homologous without side chains, with an absorption maximum at 371 nm. The emission maximum was observed at 412 nm. The quantum yield was 0.50 – 0.52 indicating that, there is no photo – induced cis – trans isomerization.