Electronic and Optical Properties of Polythiophene Molecules and Derivatives

Huai-Wen Tsai,Che-Wun Hong,Mei-Hsin Chen,Kan-Lin Hsueh

doi:10.3390/cryst11111292

Abstract

The electronic and optical properties of polythiophene (PT) for polymer light-emitting diodes (PLEDs) were calculated using density functional theory (DFT) and time-dependent DFT. We calculated the electronic and optical properties of thiophene and PT polymers with degrees of polymerization (DP) from 2 to 30 monomers (T1–T30) and their derivatives. The associated highest occupied molecular orbital (HOMO) energy, lowest unoccupied molecular orbital (LUMO) energy, band gaps, electron orbitals, and molecular structures were determined. As the DP increased, the LUMO energy gradually decreased, and the HOMO energy gradually increased. The band gap of PT approached 2 eV as the DP of the PT polymer increased from 1 to 30. The calculations and exchange–correlation functional were verified against values in the literature and experimental data from cyclic voltammetry (redox potential) and ultraviolet-visible, photoluminescence, and ultraviolet photoelectron spectra. The color of PT PLEDs can be adjusted by controlling the DP of the polymer and the substituents.

Highlights

The quantum efficiency of polymer light-emitting diodes (PLEDs) can reach up to 8%, and their driving voltage is lower as compared to other LEDs
The simulation method was used to derive the properties of the PT, which is a linear polymer composed of multiple thiophene monomers
Five substituents were chosen for this study: the strong electron-donating group (OCH3), electron-donating group (OCOCH3), weak electron-donating group (CH3), weak electron-withdrawing group (Br), substitution comes in many forms

Summary

Introduction

Polymer light-emitting diodes (PLEDs) were developed in the Cavendish Lab Burroughs of the University of Cambridge in 1990 using the spin coating method [1]. The quantum efficiency of PLEDs can reach up to 8%, and their driving voltage is lower as compared to other LEDs. Developing PLEDs is simple because a vacuum is not required. During the development of such materials, the molecular structure can be changed using different methods of synthesis to obtain PLEDs of different materials with various functionalization. By changing the molecular bond length [2], adding a launching group to control the color of the wavelength, or adding various groups for electron transport to improve carrier injection, the efficiency of illumination [3] or functionalization can be improved

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