Semi-empirical study of two-color fluorescent dyes based on 3-hydroxychromone

Extensive study of eight 3-hydroxychromone derivatives designed as fluorescence dyes for the hydrophobic range of polarities is performed. The properties of the ground and excited states of both normal (N) and tautomeric (T) forms are calculated in vacuum and in the solvent media approximated as continuous dielectrics. The determined molecular properties and obtained values of absorption and emission wavelengths are compared with experimental data. It is shown that semi-empirical AM1 method captures essential trends in molecular properties of 3HC dyes the electronic structures of which are modulated by the presence of substituents. Calculated energy differences between N* and T* (and N and T) forms and between ground and excited states are qualitatively consistent with the experimental data. Meantime, a systematic deviation is observed for the calculated emission wavelengths from the T* state. Thus semi-empirical methods can be used to search for 3HC derivatives with the desired properties by comparing the calculated spectra of the tested compounds with the existent experimental data.