Vibration frequencies of perylene with different molecular charges

Abstract EN

The (B3LYP) Density Functional Theory (DFT) method was applied for calculating the vibration frequencies and normal coordinates of the neutral aromatic perylene molecule as well as its radical cation and anion.

Comparison of the results showed that for the C-H stretching vibrations, the symmetric mode shows higher frequency values than its corresponding asymmetric.

As for the C-C stretch, as well as the δCH and δCC deformation vibrations the asymmetric vibrations were of higher frequencies than the symmetric one.

Comparing the frequencies of the three differently charged species with each other, it was found that; νCH str.

·+ > νCH str.

○ > νCH str.

·- and, νsym CC str.

> νsym CC str.

˙ + > νsym CC str.˙ ¯ for some modes; and; νsym CC str.·+ > νsym CC str.

> νsym CC str.·¯ for other modes.

These relations are discussed in terms of the change in the σ electron densities at the H atoms of the C-H bonds and the changes in the bond orders of the related C-C bonds.