Absorption Spectra of Azobenzenes Simulated With Time-Dependent Density Functional Theory

Using time-dependent density functional theory and the polarizable continuum model, we have simulated the absorption spectra of an extended series of azobenzene dyes. First, we have determined a theoretical level optimal for this important class of dyes, and it turned out that a C-PCM-CAM-B3LYP/6-311+G(d,p)//C-PCM-B3LYP/6-311G(d,p) approach represents an effective compromise between chemical accuracy and computational cost. In a second stage, we have compared the theoretical and experimental transition energies for 46 n -> pi* and 141 pi -> pi* excitations. For the full set, that spans over a 302-565 nm domain, we obtained a mean absolute deviation of 13 nm (0.10 eV) and a linear correlation coefficient of 0.95, illustrating the accuracy of our approach, though some significant outliers pertained. In a last step, the impact of several modifications, that is, trans/cis isomerization, variation of the acidity of the medium and azo/hydrazo tautomerism have been modeled with two functionals. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem 111: 4224-4240, 2011