MP2 calculations of the effect of the π-conjugation on the electronic
and nonlinear optical properties of para-nitroaniline (pNA) derivatives
Abstract
long-range charge transfer organic compounds are remarkable for having
very large hyperpolarizabilities and thus improved nonlinear optical
(NLO) properties. p-nitroaniline (pNA) is known as a prototypical NLO
organic material. The question answered in this work is the NLO
properties of pNA will be improved by introducing an extended
π-conjugation chain between the phenyl ring and the two NH2/NO2
terminal? By means of sophisticated ab initio/MP2 calculations, new
derivatives of pNA with an extended π-conjugation have been designed by
introducing –(CH=CH)nNH2 or –(CH=CH)nNO2 (n = 1–5) chain into pNA.
The results indicate that introducing such chains results in smaller
energy gaps and transition energies, which lead to a significant
improvement in the hyperpolarizability (β_0). The novel pNA derivatives
exhibit larger β_0 amplitudes up to 4.67 x 104 au, which is 27-fold
greater than that of pNA. Moreover, with increasing the β_0 amplitude,
the –(CH=CH)nNO2 chain beats the –(CH=CH)nNH2 chain. It is hoped that
this study can provide a help for designing higher performance NLO
materials based on pNA.