Excited states and absorption spectra of 2-β-diketonato-1,3,2-benzodioxaborol with aromatic substituents: Quantum-chemistry modeling.

The nature of excited states of 2-β-diketonato-1,3,2-benzodioxaborol compounds with aromatic substituent have been studied by the quantum-chemical method in the approximation of the time-dependent electron density functional theory. We have measured the absorption spectra of these compounds in acetonitrile solution and compared them with the model spectra constructed on the basis of calculations. The calculations give two long-wavelength transitions with small oscillator strengths, caused by π-π transitions with the charge transfer from the benzodioxo-group to the chelate fragment. Observed long-wavelength shoulders of the spectra bands correlate with the mentioned transitions. Typical high intensity bands for π-π transitions in the ultra-violet range are caused by transitions of π-electrons in the fragments. Increasing extension of π-system gives the batochromic shift of these absorption bands and the growth of the probabilities of the transition.