Abstract
Three types of fluorescent coordination complexes of an unsymmetrical diimine ligand (LNNOH) with conjugated 14π electrons (14πe) are reported [LNNOH=(E)-2-((phenyl(pyridin-2-yl)methylene) amino)phenol]. The complexes are: [M(LNNO−)X] [M=Zn, X=Cl, 1; M=Zn, X=Br, 2; M=Cd, X=Cl, 3], [Co(LNNO−)2]Cl, [4]Cl and [Ni2(LNNOH)2(LNNO−)2]Cl2, [5]Cl2. The complexes were substantiated by elemental analyses, IR, 1H NMR, mass and UV–Vis spectra including the single crystal X-ray structure determinations of [4]Cl·H2O and [5]Cl2·2H2O. Complexes 1–3 and [4]Cl are brightly fluorescent in fluid solutions (CH2Cl2: 1, λex=475, 507nm, λem=520, 551nm, Φ=0.037, τav=2.6ns; 2, λex=474, 507nm, λem=519, 552nm, Φ=0.027, τav=2.4ns; 3, λex=474, 507nm, λem=518, 551nm, Φ=0.01, τav=2.0ns; [4]Cl, λex=472, 505nm, λem=518, 551, 601nm, Φ=0.06, τav=3.9ns) while [5]Cl2 is weakly emissive (CH2Cl2: λex=472, 506nm, λem=520, 557, 595nm, Φ=0.002, τav=1.9ns). Variable temperature magnetic measurement and Mulliken atomic spin densities obtained from unrestricted density functional theory (DFT) calculation on [5]2+ cation, are consistent with the existence of weakly interactive (J=+2.318) two Ni(II) ions. Time dependent (TD) DFT calculations on 1 and [4]+ authenticated the intra-ligand πphenolato→πdiimine∗ transitions for 1–3 and both intra- and inter-ligand πphenolato→πdiimine∗ transitions for [4]Cl as the origins of the emissive excitations.
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