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 NH 2 /NO 2 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 –(CH CH) n NH 2 or –(CH CH) n NO 2 ( 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 ( β 0 ). The novel pNA derivatives exhibit larger β 0 amplitudes up to 4.67 × 10 4 au, which is 27-fold greater than that of pNA. Moreover, with increasing β 0 amplitude, the –(CH CH) n NO 2 unit beats the –(CH CH) n NH 2 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. • The NLO properties of pNA improved by introducing an extended π-conjugation chain. • Smaller energy gaps and transition energies lead to better β 0 . • The novel pNA derivatives exhibit β 0 which is 27-fold greater than that of pNA. • With increasing the β 0 , the –(CH CH) n NO 2 unit beats the –(CH CH) n NH 2 unit.