Electronic structure, cationic, and excited states of nitrogen-containing spiroborates.

CONTEXT: This paper presents the results of the study of the electronic structure and cationic and excited states of three spiroborate complexes (2-acetylacetonato-1,3,2-benzodioxaborol, its NH- and NMe-derivatives) and three corresponding ligands (acetylacetone, 4-aminopent-3-en-2-one, and 4-methylaminopent-3-en-2-one). Materials based on spiroborates are used in medicine, for example, as a drug carrier. In industry, spiroborate anions are used in ionic liquids and as alternative high performance lubricants. Analysis of experimental and calculated data allowed determining the influence of functional groups on the parameters of the electronic structure and energy of electronic transitions. Compared to acetylacetone and its NH- and NMe-derivatives, the upper filled molecular orbitals of the corresponding spiroborates are stabilized at 0.4-1.7 eV, which is due to the positive charge of the ligand due to the acceptor properties of the dioxyphenylene fragment. Among the studied compounds, when replacing the oxygen atom in the α-position with the NH- or NMe-group, a bathochromic shift of intense bands in the absorption spectra is observed, since the energy intervals between the orbitals of the π3 and π4 ligand are reduced. In addition, in a number of spiroborates, the violation of C2v symmetry when replacing an oxygen atom leads to the appearance of a low-intensity maximum in the long-wave part of the absorption spectrum, due to the π2X → π4 transition. METHOD: Complexes were studied by photoelectron spectroscopy, absorption spectroscopy, and high-level ab initio quantum chemical computations, including the algebraic diagrammatic construction method for the polarization propagator of the second order (ADC(2)), the outer-valence Green's function (OVGF), the density functional theory (DFT), the time-dependent density functional theory (TDDFT) and the domain-based local pair natural orbital (EOM-DLPNO) methods. X-ray photoelectronic spectra of two spiroborates in the condensed state were measured using a two-chamber high-vacuum system MXPS XP (Omicron, Germany). UV-visible absorption spectra were recorded using a spectrophotometer 2550 (Shimadzu-UV, Japan). The geometry of all studied compounds was optimized by the DFT/B3LYP/Def2-SVP method. The energy of electron levels in the S0 state and the distribution of electron density at each MO were obtained by the DFT/CAMB3LYP/cc-pVDZ method. The energies of excited states were obtained by the TDDFT/CAMB3LYP/cc-pVDZ, ADC(2)/cc-pVDZ and EOM-DLPNO/cc-pVDZ methods. All DFT and TDDFT calculations were carried out in the GAMESS (US) software computing package. ADC(2) calculations of excited states were performed using the Orca 4.0.1 software package. EOM-DLPNO and OVGF calculations were carried out in the Gaussian 16 software package.

XPS and quantum chemical analysis of 4Me-BODIPY derivatives.

The results of a X-ray photoelectron spectroscopy (XPS) and steady-state absorption spectroscopy study of the electronic structure, and cationic and excited states of a series of 1,3,5,7-tetramethyl-substituted BODIPYs (4Me,2R-BODIPYs) are presented. The experimental data were interpreted using high-level ab initio quantum chemical computations, including the algebraic diagrammatic construction method for the polarization propagator of the second order (ADC(2)), the outer-valence Green's function (OVGF) method, the density functional (DFT) approach, and the time-dependent DFT (TD-DFT) approach. Substitution effects on the XPS and absorption spectra were determined for 2,6-positions of 4Me,2R-BODIPY pyrrole nuclei (R = H, Br, Bu, benzyl). A very satisfactory performance of the DFT Koopmans theorem analogue was demonstrated with respect to the energy intervals between the electronic levels of 4Me,2R-BODIPY above 13 eV (BHHLYP functional) and the values of the HOMO-LUMO energy gap (ωB97X functional).

Photoelectron spectra and electronic structure of boron diacetate formazanates.

The electronic structure and cationic states of two 1,5-diphenylformazanes and two boron diacetate (B(OAc)2) formazanates were modeled using the outer valence Green's function (OVGF) and density functional theory (DFT) methods. Comparison of data of the OVGF and ultraviolet photoelectron spectroscopy (UPS) methods made it possible to determine an effect of functional groups and complexing agents on energies of cationic states. Addition of NO2-group at the γ-position of the chelate cycle causes stabilization of levels the five upper occupied molecular orbitals (MO) and destabilization of the bonding orbital π3Ph + π3 level. The levels of MOs π3Ph-π3 and n- are stabilized due to influence of the complexing agent B(OAc)2, with a difference in the shift of 0.67 eV. The ionization energies (In) changes for the π-orbitals of benzene rings are within the error of the OVGF method. Under methylation of phenyl groups, the differences between the calculated In, corresponding to the π-orbitals of aromatic substituents, are in good agreement with the experimental In shifts at transition from benzene to toluene. According to the OVGF method, in all the studied complexes the lowest unoccupied molecular orbital (LUMO) is localized mainly on the chelate cycle and has a strong acceptor character, which should contribute the low-lying charge-transfer electronic excitations. Moreover, an application of the DFT analog of the Koopmans' theorem with the BHHLYP and B2PLYP functionals made it possible to determine qualitatively a sequence of cationic states and energy intervals between them in the spectral range up to 10 eV. The DFT/wB97x/cc-pVTZ method data on the energy gap between the highest occupied molecular orbital (HOMO) and LUMO levels correlate with the OVGF/cc-pVTZ calculation results.