Theoretical investigation of electro-optical properties of novel D-Pi-D based organic compounds for OLED applications

This article presents the design of five new π-conjugated molecules whose structure contains a D-Pi-D succession, where the donor D unit consists of a carbazole, and the Pi unit varies according to the different donors. Parameters examined included HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) energy levels, band gap energy (Egap), frontier molecular orbitals, electron affinity and ionization potential. The results show that the Egap values of the molecules studied range from 3.34 to 4.11 eV, suggesting strong conjugation of these structures. The Time-Dependent Density Functional Theory using the B3LYP hybrid functional and the 6-311G(d,p) basis set method was used to analyze the absorption and emission properties of the compounds, highlighting various features such as their maximum wavelength (λmax), vertical excitation energy (E) and oscillation strengths (O.S), maximum emission wavelengths (λem) and fluorescence energies (EFLu). These materials exhibit broad absorption bands above 360 nm and intense emissions above 421 nm, falling into the UV–visible region. Analysis of the I–V characteristic obtained by SILVACO TCAD software indicates that a minimum voltage is required for the organic light-emitting diode (OLED) to emit light, with threshold voltages of VD = 2 V and VD = 2.2 V. The results show that Oi compounds possess promising properties, makes them potentially interesting materials for use in OLED devices. This theoretical study therefore provides a valuable framework to guide the experimental synthesis of these compounds.