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The visible spectra of a large panel of thioindigo dyes are evaluated with the polarizable continuum method (PCM) and time-dependent density functional theory (TD-DFT), using the PBE0 functional and extended atomic basis sets. It is found that the majority of the cis thioindigo dyes are planar and their hypso-character originates from repulsion of electron densities in the excited state, and the central C=O double bond length is a good indicator of the color of the substituted thioindigo

Density functional theory schemes based on conventional exchange-correlation functionals have been used to establish dipole moment, polarizability, and first and second hyperpolarizabilities of push-pull pi-conjugated systems. It is concluded that current exchange-correlation functionals do not accurately describe the polarization of conjugated systems when the polarization is the result of donor/acceptor substitution or an external field or both.

A reliable and fast computational method developed for the calculation of p[K.sub.a]* of photoacids is examined. The results obtained from the five coumarins verify the reliability of the model that is developed by combination of density functional theory (DFT) for the excited states, time-dependent DFT, with a polarizable continuum model for solvent.

The ultraviolet absorption spectra of coumarins and chromones are investigated with the PCM-time-dependent-density functional theory (PCM-TD-DFT) theoretical scheme by using three hybrid functionals and taking into account methanol or ethanol solvation effects. The results have shown that there are at least two allowed excited states presenting strong oscillator strength in the UV region, where both involve a charge transfer from the benzenic cycle to the pyranone moiety.

The UV/visible spectra of a series of indirubin, isoindigo, and other indigo/thioindigo related dyes are evaluated in various solvent environments by using the time-dependent density functional theory in conjunction with the polarizable continuum model. It is stated that even for molecules of the same family, significant differences in the excitation processes are noted.