Theoretical study of thieno-thiophene based low band gap copolymers and substituent effect on the optoelectronic properties of them.
This paper studies donor-acceptor systems which incorporate benzodithiophene (BDT), benzodifuran (BDF) and benzodipyrrole (BDP) units as the electron-rich monomer with TT unit representing the electron-deficient monomer. This research is based on employing density functional theory (DFT) and time-dependent DFT (TD-DFT). The highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO), HOMO-LUMO gaps and dihedral-angles of these copolymers were calculated using oligomer extrapolation technique and periodic boundary condition (PBC) method. The optical band gaps and UV-vis absorption spectra of aforementioned copolymers were obtained by TD-DFT at the same level of theory. Based on the fair agreement between PBC-DFT calculated results and experimental data, the substituent effects of Cl, Br, CCH, COH, NO2, OH, SH and NH2groups were investigated by PBC-DFT method. The difference between the ground and excited-states dipole moment (Δμge) of all derivatives were also calculated. Taking these results into account, a better understanding of the substituent effects on the photo-physical properties of the copolymers under study was achieved. Due to the shift of HOMO and LUMO energy levels, smaller band gaps and higher Δμgeare observed in some derivatives. The calculation results demonstrate that the substitution of COH and NO2by fluorine in BDF-TT and BDP-TT leads to higher maximum theoretical efficiencies (η).
Plasma Physics Department of Science and Research Branch, Islamic Azad University, Tehran, Iran. Electronic address: m.gavankk@gmail.com.
Mehri Javan
MJ
Khoshkholgh
Plasma Physics Department of Science and Research Branch, Islamic Azad University, Tehran, Iran.
Mohammad Reza
MR
Abolhassani
Department of Physics, Amirkabir University of Technology, PO Box 15875-4413, Tehran, Iran.
Farah
F
Marsusi
PBC-DFT; Substituent effect; TD-DFT; Thieno-thiophene based copolymers; UV–vis absorption spectra