The change of hydrogen position on pi-conjugated bridge to affect NLO property of D(-NH2)-pi(DHTPs)-A(-NO2) system

The donor-pi-conjugated bridge-acceptor (D-pi-A) is a classical framework to design high-performance organic electro-optical materials. In this work, based on the pi-conjugated dihydrotetraazapentacenes (DHTPs), four isomers (1-4) with D(-NH2)-pi(DHTPs)-A(-NO2) framework are designed and characterized. The 2 and 3 origi-nate from single-hydrogen migration of 1, and 4 derives from double-hydrogen migration of 1. Significantly, the change of hydrogen position on DHTPs bridge can affect their nonlinear optics (NLO) property. Compared with the first hyperpolarizability (beta tot) (4.08 x 103a.u.) of 1, the 6.90 x 103-2.56 x 104 a.u. of 2-4 are enhanced. More interestingly, the 4 has largest beta tot value of 2.56 x 104, which is approximately equal to the sum of 6.90 x 103 a. u. of 2 and 1.82 x 104 a.u. of 3. Furthermore, the change of hydrogen position on DHTPs brings some distinctive changes in their geometric structure, nucleus-independent chemical shifts (NICS) value, natural population analysis (NPA) charge, UV-vis absorption spectrum along with its other electronic property that might be beneficial to explore their structure-property relationships.