Quantum chemical investigations study of the effect of electron donor units on the structural, electronic and optoelectronic properties of diarylthienopyrazine analogs

The structural and electronic properties of thienopyrazine–thiophene copolymer (TP) are studied by means of quantum chemical calculations based on density functional theory (DFT) using B3LYP functional with 6-31G(d,p) for all atoms and all states (ground, excited and doped). The study of the geometrical parameters (dihedral angle, bond length), ground, and doped states (p, n) showed that the structures of these oligomers are planar. er, the electronic properties (HOMO, LUMO, Egap, EA, IP … ) were determined from the fully optimized structures. The absorption and emission of these copolymers are calculated using TD-B3LYP/6-31G(d,p) method. It is found that the structure of diarylthieno 2.3-[3,4-b] pyrazine analogs (TPi with i = 1–5) is planar in these excited states. The S1/S0 electronic excitation is characterized as a highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) transition and is distinguishing in terms of oscillator strength. Fluorescence energies of TPi are calculated from TD-DFT method. This fundamental information is a valuable data in designing and making promising materials for LED materials.