In the approximation of the time-dependent electron density functional theory, we have studied using the quantum-chemical method the nature of excited states of boron difluoride acetylacetonate F2B(AA) and its substituted derivatives that contain aromatic groups with one or two benzene cycles in the β-position [1]. Optimization of the geometry of complexes show coplanar positions of cycles for all compounds, except for that with the substituent C6H3(CH3)2 and C6H4C6H5. Based on the calculated transition energies and oscillator strengths, we have simulated the absorption spectra in the prevacuum range. The calculated absorption spectra have been compared with the experimental spectra in the gas phase or in solutions. As the π system becomes more extended, a bathochromic shift of the first absorption band and an increase in the transition probability are observed. Structure, compounds and their calculated energy of excitation E and oscillator strength f for the first π-π* transition are in the table.tableIn compounds II–VII, the first absorption bands with a maximal intensity are caused by transitions of π-electrons from the HOMO, which is delocalized over the chelate cycle and the substituent, to the LUMO with a predominant contribution of the π4 orbital of the chelate cycle. According to the calculation results, the contributions of AOs of the substituent to the HOMO increase from 33% in compound II to 63% in IV, and to 86% in V–VII. Transitions with the transfer of the electron density from π3 orbital of the chelate cycle to unoccupied π* MOs of aromatic substituents in the prevacuum range are not numerous and have oscillator strengths that do not exceed 10–1 . The excited states π-π*, which are localized predominantly on aromatic cycles, were predicted in the prevacuum range only for complexes V–VII with conjugated benzene cycles. Their oscillator strength is two orders of magnitude lower than the value of this parameter for first charge transfer transitions. The energy of transitions n-π*, lies in the interval 4.48–4.55 eV, while the value of their oscillator strength is about 10–4 , except for complex IV, the structure of which is acoplanar.