Jiwon Moon

Benchmark Study of Density Functional Theory for Neutral Gold Clusters, Aun (n = 2–8)

Neutral gold clusters, Aun (n = 2-8), were optimized using coupled cluster singles and doubles with perturbative triples (CCSD(T)) with a triple-ζ-level basis set to develop reliable reference values for their structural and energy parameters in order to assess the performance of density functionals. The performance of 44 density functional theory (DFT) methods for calculating molecular structures and relative energies is assessed with respect to CCSD(T). In addition, their performance when calculating vertical ionization potentials (vIPs) of Aun (n = 2-8) is also assessed by comparison with experimental values. The revTPSS functional shows good performance for calculating both the structural and energy properties of Aun (n = 2-8), whereas B3P86 shows a remarkable performance in calculating the vIPs. The quadruple-ζ-level valence basis set is necessary for obtaining accurate energy values in CCSD(T) calculations.

Spin–Orbit Effect on the Molecular Properties of TeXn (X = F, Cl, Br, and I; n = 1, 2, and 4): A Density Functional Theory and Ab Initio Study

Density functional theory (DFT) and ab initio calculations, including spin-orbit coupling (SOC), were performed to investigate the spin-orbit (SO) effect on the molecular properties of tellurium halides, TeXn (X = F, Cl, Br, and I; n = 1, 2, and 4). SOC elongates the Te-X bond and slightly reduces the vibrational frequencies. Consideration of SOC leads to better agreement with experimental values. Møller-Plesset second-order perturbation theory (MP2) seriously underestimates the Te-X bond lengths. In contrast, B3LYP significantly overestimates them. SO-PBE0 and multireference configuration interactions with the Davidson correction (MRCI+Q), which include SOC via a state-interaction approach, give the Te-I bond length of TeI2 that matches the experimental value. On the basis of the calculated thermochemical energy and optimized molecular structure, TeI4 is unlikely to be stable. The use of PBE0 including SOC is strongly recommended for predicting the molecular properties of Te-containing compounds.

Direct Observation of a Transiently Formed Isomer During Iodoform Photolysis in Solution by Time-Resolved X-ray Liquidography

Photolysis of iodoform (CHI3) in solution has been extensively studied, but its reaction mechanism remains elusive. In particular, iso-iodoform (iso-CHI2-I) is formed as a product of the photolysis reaction, but its detailed structure is not known, and whether it is a major intermediate species has been controversial. Here, by using time-resolved X-ray liquidography, we determined the reaction mechanism of CHI3 photodissociation in cyclohexane as well as the structure of iso-CHI2-I. Both iso-CHI2-I and CHI2 radical were found to be formed within 100 ps with a branching ratio of 40:60. Iodine radicals (I), formed during the course of CHI3 photolysis, recombine nongeminately with either CHI2 or I. Based on our structural analysis, the I-I distance and the C-I-I angle of iso-CHI2-I were determined to be 2.922 ± 0.004 Å and 133.9 ± 0.8°, respectively.

Performance of Density Functional Theory and Relativistic Effective Core Potential for Ru-Based Organometallic Complexes.

Herein a performance assessment of density functionals used for calculating the structural and energetic parameters of bi- and trimetallic Ru-containing organometallic complexes has been performed. The performance of four popular relativistic effective core potentials (RECPs) has also been assessed. On the basis of the calculated results, the MN12-SX (range-separated hybrid functional) demonstrates good performance for calculating the molecular structures, while MN12-L (local functional) performs well for calculating the energetics, including that of the Ru-Ru bond breaking process. The choice of appropriate density functional is a crucial factor for calculating the energetics. The LANL08 demonstrates the lowest performance of the RECPs for calculating the molecular structures, especially the Ru-Ru bond length.

Identifying the major intermediate species by combining time-resolved X-ray solution scattering and X-ray absorption spectroscopy

Identifying the intermediate species along a reaction pathway is a first step towards a complete understanding of the reaction mechanism, but often this task is not trivial. There has been a strong on-going debate: which of the three intermediates, the CHI2 radical, the CHI2-I isomer, and the CHI2(+) ion, is the dominant intermediate species formed in the photolysis of iodoform (CHI3)? Herein, by combining time-resolved X-ray liquidography (TRXL) and time-resolved X-ray absorption spectroscopy (TR-XAS), we present strong evidence that the CHI2 radical is dominantly formed from the photolysis of CHI3 in methanol at 267 nm within the available time resolution of the techniques (∼20 ps for TRXL and ∼100 ps for TR-XAS). The TRXL measurement, conducted using the time-slicing scheme, detected no CHI2-I isomer within our signal-to-noise ratio, indicating that, if formed, the CHI2-I isomer must be a minor intermediate. The TR-XAS transient spectra measured at the iodine L1 and L3 edges support the same conclusion. The present work demonstrates that the application of these two complementary time-resolved X-ray methods to the same system can provide a detailed understanding of the reaction mechanism.

Theoretical Investigation of the Reaction Mechanism of the Photoisomerization of 1,2‐Dihydro‐1,2‐azaborine

The photoisomerization of 1,2-dihydro-1,2-azaborine was investigated by high-level multireference ab initio and density functional theory calculations. The intermediates (IMs) and transition states (TSs) on the S(0) and S(1) states were optimized using the state-averaged complete active space self-consistent field method. The multireference configuration interaction method with the Davidson correction was used to obtain accurate energetics. Moreover, the conical intersections (CIs), which play a crucial role in photoisomerization, were also optimized. On the basis of the calculation results, the most favorable proposed reaction pathway is as follows: reactant→Franck-Condon region→TS(1) →CI→IM(0) →TS(0P) →product. The product was not directly formed through the CI, and the IM(0) existed on the S(0) state. These results show that the isomerization of 1,2-dihydro-1,2-azaborine involves both photoreactions and thermal reactions. The calculated results clarify recent experimental observations.

Density functional and ab initio study of samarium dihalides, SmX2 (X = I, Br, and Cl)

ABSTRACT Quantum chemical calculations were performed to identify the closely lying septet electronic states of SmX2 (X = I, Br, and Cl) and their electronic structures were analysed. According to high-level ab initio calculations, the ground state of SmX2 (X = I, Br, and Cl) is the 7B1(2) state. The molecular structures of SmX2 (X = I, Br, and Cl) as optimised by B1B95 are very close to those obtained using coupled-cluster singles and doubles including perturbative corrections for the triple excitations (CCSD(T)). Since the electronic states of SmX2 (X = I, Br, and Cl) are quite close, the thermal average should be considered to compare the calculated results with the experimental ones. Descriptions of the molecular properties of SmX2 (X = I, Br, and Cl) are correlated to the ability to accurately describe the ionic bonding character of SmX2 (X = I, Br, and Cl). GRAPHICAL ABSTRACT

Effect of phosphorus on the electronic and optical properties of naphthoxaphospholes: theoretical investigation

ABSTRACT Density functional theory (DFT) and time-dependent DFT calculations were performed to elucidate the electronic and optical properties of 2-R-naphthol[2,3-d]oxaphospholes (R-NOPs). On the basis of the calculated results, the poor π overlap between the 3pz orbital of P atom and the 2pz orbitals of other atoms and increasing polarity of P atom result in a reduced energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. When these two effects are considered simultaneously, the absorption energies obtained for the S1 state can be below 3.00 eV according to replace the P atom of oxaphosphole ring by As atom (increasing the poor π overlap) and change the functional groups (increasing polarity). The origin of these two effects is the inherent size of the 3p orbital of P atom. The role of P atom in the control of the electronic and optical properties of R-NOPs is clearly elucidated.

Reaction mechanism of cyanoethynyl radical (C3N) with ethylene (C2H4) to form C5H3N and H: a theoretical investigation

The reaction mechanisms of cyanoethynyl radical (C3N) with ethylene (C2H4) to form C5H3N and H were investigated using density functional theory and a high-level ab initio method such as the coupled-cluster singles and doubles including a perturbative estimate of triples (CCSD(T)). The reaction pathways can be categorized into three types. The first pathway includes only chain intermediates (IMs). The second pathway includes ring IMs except for pyridine-like structures. The final pathway includes the pyridine-like structures. On the basis of the calculated results, the most favorable reaction pathway is the first type; the H elimination takes place from the initial chain adduct of C3N with C2H4. Because C3N and butadinyl (C4H) radical are isoelectronic, the most favorable reaction pathway and barrier energy of the reaction of C3N with C2H4 are almost identical to those of the reaction of C4H with C2H4.

Achieving a high-efficiency dual-core chromophore for emission of blue light by testing different side groups and substitution positions

Hetero dual-core derivatives that combine anthracene and pyrene were systematically studied for the purpose of producing highly efficient blue light-emitting materials applicable to organic light-emitting diode (OLED) lighting. Five compounds were designed in order to (1) determine which one of the two core chromophores in a hetero dual-core moiety, if any, acts as the main contributor to the optical and electronic properties of the final compounds, (2) control the electron-donating ability of the side group, and (3) change the substitution position. 1-[1,1′;3′,1′′]terphenyl-5′-yl-6-(10-[1,1′;3′,1′′]terphenyl-5′-yl-anthracen-9-yl)-pyrene (TP-AP-TP) was used as the reference material, and four other materials, including diphenyl-[10-(6-[1,1′;3′,1′′]terphenyl-5′-yl-pyren-1-yl)-anthracen-9-yl]-amine (DPA-AP-TP), diphenyl-[6-(10-[1,1′;3′,1′′]terphenyl-5′-yl-anthracen-9-yl)-pyren-1-yl]-amine (TP-AP-DPA), diphenyl-{4-[10-(6-[1,1′;3′,1′′]-terphenyl-5′-yl-pyren-1-yl)-anthracen-9-yl]-phenyl}-amine (TPA-AP-TP) and diphenyl-{4-[6-(10-[1,1′;3′,1′′]terphenyl-5′-yl-anthracen-9-yl)-pyren-1-yl]-phenyl}-amine (TP-AP-TPA), were synthesized as model compounds. The synthesized materials showed absorption wavelength peaks at 403–410 nm in the film state and exhibited PL emissions of 458–505 nm. Also, anthracene was shown to be the main core contributing to the optical and electronic properties. Among the synthesized molecules, the TPA-AP-TP molecule, in which triphenylamine, with its optimum electron-donating ability, was substituted into anthracene, showed excellent electroluminescence (EL) performance for OLED lighting with a current efficiency of 8.05 cd A−1, external quantum efficiency of 6.75%, and narrow EL FWHM of 53 nm.