Results

The quantum-chemical calculation of the basic and excited states of molecules were put by semiempirical method with intermediate neglect of differential overlap (INDO) involving special spectroscopic parametrization [1-3]. Designed by us the energy and intensity of transitions have allowed to construct the energy schemes of electronic excited states of 4MU and its protolytic forms, and constants obtained of internal conversion (k_ic) and matrix elements calculated using of matrix elements of spin-orbital interaction constant of intercrossing conversion (k_ST) to assume ways of deactivation energy of excitation in the given structures ([4-6], Fig. 2, Table 1). The analysis of distribution of electronic density in basic and various electronic states allows to conclude, that at excitation in Frank-Condone S₁* in the neutral form there is the transfer of electronic density from a phenolic ring of a molecule (aromatic ring and its hydroxygroup) to a pyronic ring, that raises probability its hydroxygroup to interrupe proton, and the pyronic part to attach, therefore at excitation existence the ionic forms, such as (A^-)* and (PhT₁)* (Fig. 1) is possible, at existence in the basic state only the neutral form (Table 2). A structure of the pyronic ring (PhT₁)* is different , than one in other protolytic forms: instead of carbonyl oxygen in its structure there is the hydroxygroup. The nature of the first singlet transition, though has charge transfer character, but direction of the transfer is different: electronic density increases on the pyronic ring and hydroxygroup and decreases on the aromatic part and oxygen of carbonyl group, that results in reduction of value of dipole moments in the excited states pp*- type. A molecule in (PhT₁)* form is less polar in excited states, than in the basic state.