Soluble Thiophene Based Poly(azomethines): Synthesis, Properties, and Theoretical Electronic Structures
Date Issued
2004
Date
2004
Author(s)
Tsai, Fu-Chuan
DOI
en-US
Abstract
Poly(azomethines) are a class of high performance polymers due to their interesting physical properties. The electronic, optical and nonlinear optical properties have been reported in the literature. However, the theoretical electronic structures of conjugated poly(azomethines) have not been investigated yet. Besides, the parent conjugated poly(azomethines) requires complicated processing solvent for processing into thin films, such as strong proton acid or Lewis Acid complexation. Hence, the development of new conjugated poly(azomethines) soluble in organic solvent is required. In this study, theoretical and experimental characterization on the soluble thiophene based conjugated poly(azomethines) were studied.
In the theoretical part, the effects of the linkage and donor/acceptor substituent or ring on the electronic properties of poly(azomethines) were studied. Poly(p-phenylene vinylene) (PPV) and poly(azine) (PAZ) show a coplanar conformation but poly(1,4-phenylene-methylidynenitrilo-1,4-phenylenenitrilomethylidene) (PPI) exhibits a twisted conformation. The nonplanar conformation in the PPI is attributed to the repulsion force between the adjacent hydrogen atoms on the C=N linkage and the N-phenylene. The bandgaps of the studied poly(azomethines) are in the range of 2.35~2.66 eV. All the substituted poly(azomethines) exhibit larger torsional angles than the parent material PTPI. Besides, there is no improvement on tuning the electronic structure due to twisted conformation if the phenylene on the backbone is replaced by the electron-accepting pyridine or the electron-donating naphthalene.
In the experimental part, four soluble thiophene based poly(azomethines) were synthesized and characterized. The absorption band edge of the polymer solution and that of the thin films was in the range 2.36~2.44 eV and 2.25~2.31 eV, respectively. The electrochemically determined HOMO-LUMO bandgap of polymer thin films was in the range of 2.23~2.29 eV. The bandgaps of the four prepared polymers are slightly larger than the parent material PHTPI. The bandgaps of the prepared polymers with various donor/acceptor substituents showed insignificant variation but slightly larger than that of the unsubstituted phenylene based poly(azomethine). The twisted conformation induced by the substitution might account for the trend of the bandgap.
Moreover, the nonplanar conformation in the poly(azomethines) system can be significantly improved if both the aromatic rings are thiophene rings or thiophene derivatives. In such case, the repulsion force between the adjacent hydrogen atoms on the C=N linkage and the N-phenylene that exists in the aromatic poly(azomethines) would be eliminated, leading to much smaller bandgaps of 1.42 eV and 1.10 eV for PTTI and PEDOTI, respectively.
Subjects
電子結構
聚甲亞胺
electronic structure
poly(azomethines)
polymer
Type
thesis