DFT/TD-DFT study on halogen doping and solvent contributions to the structural and optoelectronic properties of poly[3,6-carbazole] and poly[indolo(3,2-b)-carbazole]

The polycarbazoles have been proved to be a good organic semiconductor. These are investigated by quantum chemical studies using B3LYP density functional theory (DFT), and the studies have given a detailed understanding on the impact of carbazole units and an introduction to the electron donating on the optoelectronic properties. The electron withdrawing groups of halogen atoms (chlorine, bromine and iodine) have been substituted into the side chain of the poly[3,6-carbazoles] (PCs) and poly[indolo(3,2-b)-carbazoles] (PICs) and analysed. The band was assigned in the gas phase at 354.8 and 365.1nm for PCs and PICs which are in good agreement with experimental values of 350 and 390nm. The calculated results show that the selected three halogen derivatives exhibit a strong blue shift in the toluene solvent medium, with high electronic transition. It is found that PCs, PICs and their derivatives have a narrow band derived in the conduction band, and it is composed of 3p, 4p and 5p states; thus, the energy gap of PCs and PICs increased between the highest occupied molecular orbital and lowest unoccupied molecular orbital energy level by the addition of electron acceptor group atoms. The doped PC and PIC electronegativities are well plotted by an electrostatic potential map, and the plot reveals that chlorine-doped PCs and PICs have less electronegativity and bromine-doped polymer has high electronegativity than that of the chlorine-doped polymers. The results obtained from these studies will expose the affairs between the molecular geometry and electronic and optical properties of the investigated polymers.