Conformers and electronic spectra of dansylamide: experimental and theoretical studies

Particular features of the geometrical and electronic structure of six possible conformers of dansylamide ((CH$_{3}$)$_{2}$N–C$_{10}$H$_{6}$–SO$_{2}$NH$_{2}$) are considered. The electronic absorption spectra of the conformers of dansylamide in the free state and taking into account the influence of an aqueous solvent (in terms of the PCM model) are calculated by the TDDFT method. It is shown that, as a result of taking into account solvation, the electronic absorption spectra of the conformers exhibit a bathochromic shift, and the difference in the values of $\lambda$ of the conformers reaches 16 nm. The calculated electronic absorption spectra in an aqueous medium agree qualitatively with the obtained experimental spectra. An analysis of molecular orbitals involved in the first three electronic transitions of the conformers is carried out. It is suggested that the broadening of the band with $\lambda_\mathrm{max}$ = 326 nm in the experimental spectrum may be caused by the presence of dansylamide conformers in the aqueous solution. It is shown that the calculated values of $\lambda$ in the electronic absorption spectra of dansylamide in the aqueous solvent depend substantially on the DFT functional type.