In this work, we theoretically design a new π-conjugated thieno[3,4-b]pyrazine derivative intended for organic electronics. The geometric, electronic, optical, photovoltaic, and nonlinear optical (NLO) properties of the studied molecule were investigated using calculations based on density functional theory (DFT) and its time-dependent variant (TD-DFT) at the B3LYP/6-31G(d,p) level. The structural modification of the reference molecule results in a small energy gap (Eg = 1.68 eV) and a significant enhancement in optical absorption in the visible region, with maxima observed at λmax = 877 nm (TD-B3LYP) and λmax = 668 nm (CAM-B3LYP).

Herein, we theoretically design four new π-conjugated thieno[3,4-b]pyrazine derivatives for organic solar cells (OSCs), denoted 2,3-di([2,2′:5′,2″:5″,2‴-quaterthiophen]-5-yl)-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine, 2,3-bis(5'''-(4-fluorophenyl)-[2,2':5',2'':5'',2'''-quaterthiophen]-5-yl)-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine, 2,3-bis(5'''-(4-methoxyphenyl)-[2,2':5',2'':5'',2'''-quaterthiophen]-5-yl)-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine, and 2,3-bis(5'''-(9-methyl-9H-carbazol-2-yl)-[2,2':5',2'':5'',2'''-quaterthiophen]-5-yl)-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine. The geometric, electronic, optical, photovoltaic, and nonlinear optical (NLO) properties of the investigated chemical structure were investigated using Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations at the B3LYP/6-31G(d,p) level. Structural changes on the chemical structure induce a narrow energy gap in the range (2.08 – 2.12 eV), and an enhancement of the absorption in the visible range (λmax = 682 – 688 nm). In addition, a low value of exciton binding energies is obtained (Eb = 0.28 – 0.31 eV). Analysis of the density of states (DOS), transition density matrix (TDM), electron localization function (ELF), and localized orbital locator (LOL) showed effective charge delocalization and donor-to-acceptor electron transfer. The photovoltaic performance was assessed using the open circuit voltage (Voc) obtained between Highest Occupied Molecular Orbital (HOMO) donor to Lowest Unoccupied Molecular Orbital (LUMO) acceptor levels and was found promising (Voc = 1.32 – 1.44 V). The large hyperpolarizability and high nonlinearity response of the NLO results also indicated the potential for these molecules to be used in various optoelectronic applications.

Due to the increasing scarcity of fossil fuels and the growing demand for energy, it has become necessary to research new renewable energy sources for high-performance organic photovoltaic materials. In this context, a series of new donor–acceptor–donor compounds, based on the thieno[3,4-b]pyrazine core unit, have been designed and theoretically investigated. Donor moieties were introduced to design novel derivatives aimed at enhancing both optical absorption and charge transport properties, denoted respectively as: PTH, PTH4PF, PTH4POME, and PTHCBZ. The geometric, electronic, optical and photovoltaic characteristics of these molecular structures have been studied in depth through extensive theoretical studies. Exhibited energy gap (EH-L =EHOMO - ELUMO) ranging from 2.48 to 2.32 eV, with absorption wavelengths (λabs) between 552 and 589 nm. The Voc obtained values ranged from 0.77 to 0.99 V, while the LHE values varied between 0.59 and 0.87. This study highlights the impact of structural modifications on the electronic and photovoltaic properties of organic molecules, providing valuable guidance for the experimental design of high-efficiency organic solar cells.