A second-order nonlinear optical material prepared through in situ hydrothermal ligand synthesis

The in situ hydrothermal reactions of ZnCl(2) with benzonitrile, 2-amino-5-cyanopyridine, and trans-2,3-dihydro-2-(4' '-cyanophenyl)-benzo[e]indole in the presence of NaN(3) and water afford two 3D-diamond-like networks, (CN(4)-C(6)H(5))(2)Zn (1) and (NH(2)-C(5)H(3)N-CN(4))(2)Zn (2), and one 2D square grid network, [(CN(4)-C(6)H(4)-C(12)H(7)N-C(5)H(4)N)(2)Zn].1.5H(2)O (3), in which these ligands gradually involve a noncenter-A-D (acceptor-donor) system, a one-center-A-D system, and a two-center-A-D system, respectively. All three compounds crystallize in noncentrosymmetric space groups (I2d for 1 and 2 and Fdd2 for 3) and display strong second harmonic generation (SHG) responses. Among the three new complexes, 3 shows the largest SHG effect, which is about 50 and 500 times that of urea and KDP (KH(2)PO(4)), respectively. The two-center-A-D system (multicenter push-pull electronic effect) in 3 may be responsible for it having the largest SHG effect. Interestingly, the three compounds exhibit strong fluorescent emissions at different wavelengths, 1 and 2 with blue fluorescent emissions at 390 and 415 nm and 3 with yellow-green fluorescent emissions at 495 and 532 nm.