Structural and spectroscopic characteristics of Pyrromethene 567 laser dye. A theoretical approach

Quantum mechanic calculations at the DFT (B3LYP) and semiempirical PM5 levels were performed to study the structural and electronic properties of Pyrromethene 567 laser dye. TD-DFT and semiempirical ZINDO and CISD methods were carried out to predict the photophysical characteristics of the dye. The effect of the solvent was evaluated by means of SCRF (PCM) and the semiempirical COSMO models in c-hexane, acetone and methanol, and the results are compared to the experimental data. Both algorithms indicate an increase of the charge separation through the chromophore π-system in the polar solvents. This result explains the increase in the dipole moment and the hypsochromic shift of the absorption and fluorescence spectral bands in polar solvents, which is also experimentally observed, inducing a diminution in the dipole transition moment.