The absorption, emission spectra as well as ground and excited states calculations of some dimethine cyanine dyes

The absorption and emission properties as well as electronic structure in the ground (S0) and excited states (S1) of seven dimethine cyanine dyes were investigated by time dependent density functional theory (TD-DFT) and configuration interaction singles (CIS) levels. The effect of water on the absorption and emission spectra of the dyes was taken into account using the polarizable continuum model (PCM). TD-DFT calculations provided a correct description of the electronic absorption spectra and showed that the dominant transitions of seven dye molecules presented a π-π* character. Scaling factor 0.72 was used on the absorption and emission wavelengths obtained by CIS method, and the scaled emission wavelengths were in good agreement with the experimental values. Compared with experimental counterparts, the average relative deviations of the absorption and emission maxima were about −2.4% and 1.7%, respectively.