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 classical 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 terminals. By applying the sophisticated MP2 calculations, pNA was engineered with π-conjugation of different lengths, and new derivatives of pNA were obtained. The π-conjugation is either –(CHCH)nNH2 or –(CHCH)nNO2 (n = 1–5) chain. The results indicate that introducing such chains results in smaller energy gaps and transition energies, which lead to a significant improvement in the hyperpolarizability (β0). The novel pNA derivatives exhibit larger β0 amplitudes up to 4.67 × 104 au, which is 27-fold greater than that of pNA. Moreover, with increasing β0 amplitude, the –(CHCH)nNO2 unit beats the –(CHCH)nNH2 unit. This study may offer assistance in designing higher performance NLO materials based on pNA.
The effect of π-conjugation on the hyperpolarizabilities of pNA derivatives. [Display omitted]
•The NLO properties of pNA improved by introducing an extended π-conjugation chain.•Smaller energy gaps and transition energies lead to better β0.•The novel pNA derivatives exhibit β0 which is 27-fold greater than that of pNA.•With increasing the β0, the –(CHCH)nNO2 unit beats the –(CHCH)nNH2 unit.