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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 F 2 BAA and its substituted derivatives that contain aromatic groups with one or two benzene cycles in the β position. Optimization of the geometry of complexes show coplanar positions of cycles for all compounds, except for that with the substituent C 6 H 3 (CH 3 ) 2 . 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. We show that, in the absorption spec tra of complexes that contain substituents with one benzene cycle, the first three bands are caused by the tran sition of π electrons of the substituent to the LUMO of the chelate cycle. In complexes with two cycles in the substituent, the number of these transitions increases to five. As the π system becomes more extended, a bathochromic shift of the first absorption band and an increase in the transition probability are observed.

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