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In this work, the effects of two TiO 2 polymorphs on the decomposition of ammonium perchlorate (NH 4 ClO 4 ) were studied experimentally and theoretically. The interactions between AP and various surfaces of TiO 2 were modeled using density functional theory (DFT) calculations. Specifically, the adsorption of AP on three rutile surfaces (1 1 0), (1 0 0), and (0 0 1), as well as two anatase surfaces (1 0 1), and (0 0 1) were modeled using cluster models, along with the decomposition of adsorbed AP into small molecules. The optimized complexes of the AP molecule on TiO 2 surfaces were very stable, indicating strong covalent and hydrogen bonding interactions, leading to highly energetic adsorption reactions. The calculated energy of adsorption (ΔE ads ) ranged from -120.23 to -301.98 kJ/mol, with highly exergonic calculated Gibbs free energy (ΔG ads ) of reaction, and highly exothermic enthalpy of reaction (ΔH ads ). The decomposition of adsorbed AP was also found to have very negative ΔE dec values between -199.08 and -380.73 kJ/mol. The values of ΔG dec and ΔH dec reveal exergonic and exothermic reactions. The adsorption of AP on TiO 2 surfaces anticipates the heat release of decomposition, in agreement with experimental results. The most common anatase surface, (1 0 1), was predicted to be more reactive for AP decomposition than the most stable rutile surface, (1 1 0), which was confirmed by experiments. DFT calculations show the mechanism for activation of the two TiO 2 polymorphs is entropy driven., (© 2024 Wiley Periodicals LLC.)

This work provides a detailed multi-component analysis of aromaticity in monosubstituted (X = CH 3 , C H 2 - , C H 2 + , NH 2 , NH - , NH + , OH, O - , and O + ) and para-homodisubstituted (X = CH 3 , CH 2 , NH 2 , NH, OH, and O) benzene derivatives. We investigate the effects of substituents using single-reference (B3LYP/DFT) and multireference (CASSCF/MRCI) methods, focusing on structural (HOMA), vibrational (AI(vib)), topological (ELF π ), electronic (MCI), magnetic (NICS), and stability (S 0 -T 1 splitting) properties. The findings reveal that appropriate π-electron-donating and π-electron-accepting substituents with suitable size and symmetry can interact with the π-system of the ring, significantly influencing π-electron delocalization. While the charge factor has a minimal impact on π-electron delocalization, the presence of a p z orbital capable of interacting with the π-electron delocalization is the primary factor leading to a deviation from the typical aromaticity characteristics observed in benzene., (© 2023 Wiley Periodicals LLC.)

Time-dependent density functional theory (TDDFT) was applied to gain insights into the electronic and vibrational spectroscopic properties of an important electron transport mediator, methyl viologen (MV 2+ ). An organic dication, MV 2+ has numerous applications in electrochemistry that include energy conversion and storage, environmental remediation, and chemical sensing and electrosynthesis. MV 2+ is easily reduced by a single electron transfer to form a radical cation species (MV •+ ), which has an intense UV-visible absorption near 600 nm. The redox properties of the MV 2+ /MV •+ couple and light-sensitivity of MV •+ have made the system appealing for photo-electrochemical energy conversion (e.g., solar hydrogen generation from water) and the study of photo-induced charge transfer processes through electronic absorption and resonance Raman spectroscopic measurements. The reported work applies leading TDDFT approaches to investigate the electronic and vibrational spectroscopic properties of MV 2+ and MV •+ . Using a conventional hybrid exchange functional (B3-LYP) and a long-range corrected hybrid exchange functional (ωB97X-D3), including with a conductor-like polarizable continuum model to account for solvation, the electronic absorption and resonance Raman spectra predicted are in good agreement with experiment. Also analyzed are the charge transfer character and natural transition orbitals derived from the TDDFT vertical excitations calculated. The findings and models developed further the understanding of the electronic properties of viologens and related organic redox mediators important in renewable energy applications and serve as a reference for guiding the interpretation of electronic absorption and Raman spectra of the ions., (© 2023 Wiley Periodicals LLC.)

The chemical stability and the low-lying singlet and triplet excited states of BN-n-acenes (n = 1-7) were studied using single reference and multireference methodologies. From the calculations, descriptors such as the singlet-triplet splitting, the natural orbital (NO) occupations and aromaticity indexes are used to provide structural and energetic analysis. The boron and nitrogen atoms form an isoelectronic pair of two carbon atoms, which was used for the complete substitution of these units in the acene series. The structural analysis confirms the effects originated from the insertion of a uniform pattern of electronegativity difference within the molecular systems. The covalent bonds tend to be strongly polarized which does not happen in the case of a carbon-only framework. This effect leads to a charge transfer between neighbor atoms resulting in a more strengthened structure, keeping the aromaticity roughly constant along the chain. The singlet-triplet splitting also agrees with this stability trend, maintaining a consistent gap value for all molecules. The BN-n-acenes molecules possess a ground state with monoconfigurational character indicating their electronic stability. The low-lying singlet excited states have charge transfer character, which proceeds from nitrogen to boron., (© 2022 Wiley Periodicals LLC.)