Polyazulenes and Polynaphthalenes: Prediction and Computational Study

The geometries, the electronic structures and the aromaticity of the [n]-azulene and [n]-naphthalene polymers were studied, by using the Density Functional Theory (DFT) and the Moller-Plesset (MP2) Pertubation Theory, for the different multiplicities (M=2S+1): singlet (S=0, closed and open shell), triplet (S=1) and quintet (S=2). The ground-states of the [n]-azulene polymers were a singlet (closed shell) for any values of n (n <= 10). The ground-states of the [n]-naphthalene polymers were a singlet (closed shell) for n <= 6 and triplet for 7 <= n <= 10. The electric dipole moment of the odd [n]-azulene polymers varied with the length of the polymer chain, while exhibiting a local minimum for [5]-azulene. The dipole of the even [n]-azulene and the (even and odd) [n]-naphthalene polymers were null by symmetry. The HOMO-LUMO gap was estimated at 0.70 eV for [n]-azulene polymers with large chain. All of the polymers had electronic transition peaks in the visible region and their maximum was red-shifted for the increasing chains. The nucleus independent chemical shift (NICS) calculations have shown that ring tension was an important factor in the aromaticity loss, as shown, for example, for the flat, the cycle, and the Mobius strip [20]-polymers. The Aromatic Stabilization Energies (ASEs) that were based on the homodesmotic and isodesmic reactions were also obtained.