χ(2) and χ(3) enhancement by arylamine substituents in aromatic conjugated polyenyne polymers

In this work, we have determined the χ⁽¹⁾, χ⁽²⁾, and χ⁽³⁾ NLO properties of NH₂substituted aromatic polyenynes in ortho, meta, and para positions. It is worth noting that Mednis-Genkin’s approximation takes into account the intraband contribution with a derivate of the dipole valence-conduction band moment transition, unlike, for example, Ward’s summation-over-sates (SOS) methodology, which considers the difference of these states. Indeed, we have selected these polymers because of the high asymmetry in their molecular wavefunction. In this way, the calculated χ⁽³⁾ values of the para-NH₂ substituted aromatic polyenyne with a higher degree of polymerization are near 1 X 10⁻⁷ esu. For its part, the ortho polymer has higher values, of the order of 1 X 10⁻⁶ esu, due to its high transition dipole moment. We have also found that the energy band distribution in the para position of these polymers produces van Hove points, which have a negligible proportion of the NLO properties, compared with singularity regions 1 and 2, which have a contribution of 100 %. These regions are due to the wavefunction coefficients’ first and second-order derivatives. Besides, without considering border effects nor correlation effects, and only the variation of excitation energy, we have calculated that the quaternary monomeric oligomers of these polymers have almost similar values of χ⁽²⁾ and χ⁽³⁾. Then, it implies building a methodology to synthesize the polymers to avoid canceling the NLO-χ⁽²⁾ and -χ⁽³⁾ values.