Effects of the ratio and arrangement of donor and acceptor on the electronic and optical properties of conjugated polymers
Date Issued
2015
Date
2015
Author(s)
Liu, Yu-Hsuan
Abstract
Since the conformation of conjugated polymer can greatly affect electronic and optical properties, we employed all-atom molecular dynamics (AAMD) simulation chain conformation and quantum mechanical (QM) methods to explore the effects of the ratio and arrangement of donor/acceptor on the electronic and optical properties of conjugated polymers. In the study of poly(thieno[3,4-b]pyrazine) (PTP), the low band gaps observed in TP homopolymer materials are typically attributed to the fused-ring of the backbone and the oligomer series revealed broad absorption, significantly red-sifted by approximately 120~150 nm with each additional TP unit. Hence it is currently common for TP to be utilized as an ‘acceptor’ unit in a ‘donor-acceptor’ pair. In order to probe the extent and nature of ‘donor-acceptor’ properties , thiophene monomer and thieno[3,4-b]pyrazine monomer has been simulated. Through the study of monomer, when thiophene and thienopyrazine binding to form ‘donor-acceptor’, results in a lower bandgap due to the orbital mixing of the donor and the acceptor units, the UV-visible absorption spectrum reveal wide range (200~700 nm). The characteristics of these materials provide further insight to the electronic and optical properties through varying the ratio and arrangement of P3HT and PTP. In this study, we employed AAMD to simulate the conformation of different ratio and arrangement of donor/acceptor conjugated polymer and analyze the torsion angle distribution on the main chain. In the case of the series, the long alkyl side chain on both P3HT and PTP results in more conformational flexibility, resulting in wide range distribution of main chain torsion angles. Then we employed QM to calculate UV-visible absorption spectrum and molecule orbital energy. These results demonstrate the fact that the content of acceptor increase, the overall absorption range becomes broad, and the bandgap becomes small. The absorption spectrum of alternative versus block, alternative reveals red shift, simultaneously, the band gap is smaller. Only if the alternative polymer chain reveals big torsion deviation, block copolymer shows red shift and small bandgap.
Subjects
conjugated polymer
donor-acceptor
all atom molecular dynamics
quamtum mechmical
Type
thesis
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