Electronic structure of binuclear acetylacetonates of boron difluoride

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 π₃^Ph + π₃ level. The levels of MOs π₃^Ph-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 (I_n) 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 I_n, corresponding to the π-orbitals of aromatic substituents, are in good agreement with the experimental I_n 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.

Theoretical insights into UV-Vis absorption spectra of difluoroboron β-diketonates with an extended π system: An analysis based on DFT and TD-DFT calculations

The UV-Vis absorption spectra of difluoroboron β-diketonates with aromatic substituents at the β-carbon are studied thoroughly using DFT and TD-DFT with the CAM-B3LYP functional. The complicated experimental spectra of these dyes can be correctly interpreted by considering their structural features. A closer look at the calculated data shows that the conformational flexibility of these compounds markedly influences their spectral shape. For the complexes with an extended π system, several conformers with significantly different absorption spectra are present in the equilibrium mixture in solution. Introducing a donor group alters the electronic structure of the complexes, so the charge distribution asymmetry in the molecules increases and the nature of the electronic transitions changes. Thus, both types of substituents, aromatic and donor ones, affect the spectral shape. Understanding their roles may help one to explain the absorption spectra of these and similar compounds and predict their response to analytes and other factors.

Spectroscopic and quantum chemical study of difluoroboron β-diketonate luminophores: Isomeric acetylnaphtholate chelates

The electronic structure and optical properties of the isomeric difluoroboron β-diketonates, 2,2-difluoro-4-methylnaphtho-[2,1-e]-1,3,2-dioxaborin (I) and 2,2-difluoro-4-methylnaphtho-[1,2-e]-1,3,2-dioxaborin (II), were studied by means of X-ray photoelectron, absorption and luminescence spectroscopies. The experimental results were interpreted using high-level ab initio quantum chemical computations, including the algebraic-diagrammatic construction method for the polarization propagator of the second and third orders (ADC(2) and ADC(3)), the outer-valence Green's function (OVGF) method, and the time-dependent density functional (TDDFT) approach. The X-ray photoelectron measurements were assigned in the entire energy range using the results of the Kohn-Sham orbital calculations which employed the B3LYP functional. Pronounced hypsochromic shift of crystal-state fluorescence was observed in I upon the lowering of temperature, which can be explained by the deterioration of the conditions for excimers formation. According to our results, remarkable feature of II, absent in I, is its phosphorescence at room temperature. Basing on our calculations, a decay mechanism for the S₁ state was proposed, explaining the observed differences in the phosphorescence of I and II.