A DFT study of charge-transfer and opto-electronic properties of some new materials involving carbazole units

We have designed new conjugated copolymers, based on Phenylene-thiophene oligomers coupled with the electron-rich carbazole (Cz) units. Different configurations have been studied via (3,6)-carbazole, (2,7)-carbazole and (9N)-carbazole position linkage. Based on Density Functional Theory (DFT) and using B3LYP method, the functionalisation with carbazole units deeply improve the electronic and optical properties of the resulting compounds. Different characteristics, such as structural parameters, electronic properties, HOMO-LUMO gaps, molecular orbital densities, ionization potentials (IPs), electronic affinities (EAs), reorganization energies (λhole and λelectron) and charge transport rate (khole/electron) are determined. The lowest excitation energies and the maximal absorption and emission wavelength (λmaxABS, λmaxEM) are also underlined using the time-dependent density functional theory (TDDFT) method. The correlation of these different results shows that the introduction of the carbazole unit in the chain backbone improves the electron/hole transport proprieties and so enhances the performance of optoelectronic devices based on these compounds.