Design and synthesis of a series of N-donor quinacridone derivatives with novel nonlinear optical properties

In this work, five new quinacridone (QA)-based dyes containing a N-donor moiety have been synthesized, defined as C12QA–F, C12QA–G, C12QA–H, C12QA–I and C12QA–J, for the application of third-order nonlinear optical (NLO) responses. A new design has been put forward with the first step of connecting a long alkyl chain on the planar structure of parent ring of QA, with the aim to increase the solubility of the compound and reduce its π-π intermolecular stacking and the second step of connecting N-donor groups to enhance the effect of molecule. Electrochemical measurement data indicated that the tuning of the HOMO and LUMO energy levels can be easily realized by introducing the N-donor moiety. The theoretical calculations showed a smaller dihedral angle between the QA moiety and the N-donor than the usual, implying an excellent planarity between the two groups, which is beneficial for the intramolecular charge transfer (ICT). NLO tested under similar Z-scan measurements conditions showed that, the second-order hyperpolarizability (γ) of the five synthesized compounds ranged from 2.136 × 10−33 esu to 13.856 × 10−33 esu, with the maximum of C12QA-H was more than 13 times higher than N,N-di(n-dodecane) quinacridone(C12QA) of 0.964 × 10−33 esu. The results suggested that the designed QA-based compounds had good thermal stability and superior third-order NLO properties, very promising for integrated NLO devices.