Author: Kennedy Ogueri

Publisher:

Published: 2020

Total Pages:

ISBN-13:

ABSTRACT Organic Semiconducting Oligothiophenes and Thiophene-Based Polyphosphazenes: Synthesis, Characterization, and Application by Kennedy S. Ogueri This work involves the synthesis and characterization of thiophene-based materials as well as their photochemistry with a view toward application in organic electronics. 2,5-Bis(trimethyltin)-thieno[3,2-b]thiophene (BTTT) oligomers were prepared by Stille coupling using a palladium catalyst. A combination of proton NMR, MALD-TOF, and optical spectroscopy was used to examine the systems. Steady-state fluorescence quenching behavior of BTTT dimers (with an alkyl side chain of C6 and C12) in the presence of four different n-type dopants (PC70BM, PC60BM, F4TCNQ, TCNQ) was studied in chloroform. At room temperature, in chloroform, BTTT dimers show fluorescence with a distinct peak at around 530 nm with a natural lifetime [tau]o ~ 6.907 x10-10 sec. The addition of dopant as a quencher to a solution of BTTT dimer does not form a complex in the ground state, and its excited state shows an efficient decrease in fluorescence intensity without distorting the shape and peak position of the fluorescence band. The fluorescence quenching reaction follows Stern-Volmer kinetics. The determined fluorescence quenching rate constants range from 1.91 x 1012 Lmol-1s-1 to 1.98 x 1014 Lmol-1s-1. The quenching mechanism is an oxidative process-electron transfer occurs from the singlet excited state of the dimers to the ground state of the dopant in chloroform. This study helps in the understanding of the nature of electrical doping by charge transfer in organic semiconductors. In an extension of this work, a new class of polyphosphazene electroactive materials was synthesized via macromolecular substitution, which integrates a --P=N- backbone with thiophene based side groups. The model reactions between the small-molecule cyclic phosphazene and each of the thiophene substituents were carried out first before applying the reaction to the high polymers. The synthesized thiophene-based polymers were subjected to chemical oxidation (oxidative coupling) to optimize their optical and electronic properties through side-chain chemistry. The redox interactions of the oxidized thiophene-based polyphosphazene with four different dopants were investigated, and their quenching coefficients determined. Furthermore, the fluorescence quenching interactions (except P1/F4TCNQ and P1/TCNQ) obey Stern-Volmer kinetics. Just like the BTTT systems, the quenching mechanism, in this case, is also an oxidative process (electron transfer transpires from the singlet excited state of the polymers to the ground state of the dopant in THF). These results lend credence to the application of thiophene-based polyphosphazene to organic electronics.