چكيده لاتين
Abstract
In this study, the photophysical and optoelectronic properties of different organic and inorganic compounds have been investigated with a focus on emission mechanisms, phosphorescence, and singlet–triplet inversion (IST), using density functional theory (DFT), time-dependent DFT (TD-DFT), and ab initio quantum chemical methods to assess their potential applicability in organic light-emitting diodes (OLEDs).
In the first sections, two series of platinum (II) complexes based on bidentate 2-phenylpyridine (ppy) and 7,8-benzoquinoline (bzq) ligands have been examined. Structural analysis revealed that these complexes maintain good geometric stability in the lowest triplet excited state (T1), and minor coordinate changes upon excitation minimize nonradiative energy loss. Simulated absorption spectra indicate that the electronic transitions are primarily of MLCT, ILCT, and LLCT character and show good agreement with experimental data. Analysis of the HOMO and LUMO orbitals demonstrate that their electron density distribution and proper overlap optimize charge transfer pathways and carrier mobility. Regarding emission, the phosphorescence spectra have been predicted in the green-to-red region, with the dominant transitions in most complexes being ³MLCT/³ILCT. High spin–orbit coupling (SOC) values and suitable singlet–triplet energy gaps facilitate intersystem crossing (ISC) and enhance phosphorescence quantum yields. These features, together with the favorable alignment of the complexes’ energy levels with common OLED materials, provide ideal conditions for efficient charge transport and suppression of energy back-transfer, highlighting the high potential of these complexes for high-efficiency OLED applications.
In the third section, new frameworks based on polycyclic aromatic hydrocarbons (PAHs) with targeted boron–nitrogen (B–N) substitution have been designed and analyzed. High-level calculations (ADC(2), CC2, CASPT2, and TD-DFT) showed that incorporating triangularly arranged B–N units not only preserve singlet–triplet inversion (IST) but also enhances it, reducing the ΔST gap in some cases to –0.29 eV. The decrease in HOMO–LUMO overlap and the reduction of the exchange integral (KHL) were identified as key factors in stabilizing and reinforcing IST. Furthermore, the SOS-RSX-QIDH functional was introduced as a precise and reliable tool for predicting IST behavior, showing excellent agreement with wavefunction-based methods.
