Azo-group dihedral angle torsion dependence on temperature: A theorerical–experimental study

Quantum chemical calculations were carried out to explain the observed shifts in the absorption spectrum of different azo-aromatic compounds due to changes in the dihedral angle of the azo-group. Our results reveal that the π−π∗ transition presents a hypsochromic shift and an oscillator strength drop upon increase of the dihedral angle. Nevertheless, the n−π∗ transition exhibits the opposite behavior. This effect is attributed to the reduction in the π−electron conjugation length of the molecule. Experimentally, we performed temperature dependence measurements of the linear absorption spectrum. Both the theoretical and experimental results demonstrate that small energy changes are mirrored in the electronic transitions of conjugated linear molecules.