Visible Light-induced Photoluminescence of a Zinc(Ⅱ) Complex of N-methyl-4,4-bipyridinium Cation

Compounds with visible-light-induced photoluminescence are particularly attractive in acting as the emitting components of light-emitting diodes and fluorescent probes for biological applications. A new complex [Zn(NCS)_3(MQ)](MQ^+ = N-methyl-4,4?-bipyridinium) with an isolated molecular structure has been hydrothermally synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy and solid-state photoluminescent determination. Crystal data: C_(14)H_(11)N_5S_3Zn, M_r = 410.83, monoclinic, space group P2_1/c, a = 8.809(5), b = 13.138(7), c = 15.580(9) ?, b = 104.433(10)°, V = 1746.2(17) ?~3, Z = 4, D–c = 1.563 g×cm^3, μ = 1.769 mm^(–1), F(000) = 832, the final R = 0.0376 and wR = 0.1243 for 2850 observed reflections with I > 2s(I). In the crystal structure, the zinc atom is tetrahedrally coordinated by one MQ+ ligand and three NCS– groups to yield a tetrahedral configuration. The bond length of Zn–NMQ is clearly shorter than those found in reported Zn(Ⅱ) complexes of 4,4?-bipy. The isolated units are joined by C–H···S interactions to generate a 2D hydrogen-bonding network. This compound displays visible light-induced photoluminescence, which originates from both intraligand charge-transfer of the MQ+ ligand and NCS~–→MQ^+ charge-transfer according to a density of states(DOS) calculation. Moreover, its emission band shows a clear blue shift compared with those of halide compounds.