Journal
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY
Volume -, Issue 18, Pages 2714-2722Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/ejic.201000100
Keywords
Zinc; Schiff bases; Lanthanides; Luminescence; Energy transfer
Categories
Funding
- National Natural Science Foundation [20871098]
- Provincial Key Item of Shaanxi
- Provincial Natural Foundation of Shaanxi [2007B03]
- Education Committee Foundation of Shaanxi Province [07JK391]
- Graduate Cross-discipline Funds [07YJC11, 09YJC23]
- Northwest University [08YZZ48]
- Hong Kong Research Grants Council in P. R. China [HKBU 202407]
- Welch Foundation [F 816]
- Texas Higher Education Coordinating Board [ARP 003658-0010-2006]
- Petroleum Research Fund [47014-AC5]
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In the presence of excess pyridine (py), Zn(OAc)(2)center dot 2H(2)O reacted with an equimolar amount of asymmetric salen-type Schiff base ligand, generated in situ front the condensation of 2,3-diaminophenol with o-vanillin or 5-bromo-3-methoxybenzaldehyde, to give the d-block complex ligand [Zn(HL1)(py)] or [Zn(HL2)(py)], respectively. Interaction of [Zn(HL1)(py)] or [Zn(HL2)(py)] with Ln(NO3)(3)center dot 6H(2)O in a 1:1 molar ratio gave the cyclic hetero-tetranuclear complexes [Zn-2(L-1)(2)(py)(2)Ln(2)(NO3)(4)(dmf)(2)]center dot 3Et(2)O (Ln = Nd, 1; Yb, 2; Er, 3; and Gd, 4) or [Zn-2(L-2)(2)Ln(2)(NO3)(4)(dmf)(4)] (Ln = Nd, 5; Yb, 6; Er, 7; and Gd, 8), respectively, in moderate yields. Photophysical studies of these cyclic Zn(2)Ln(2) tetranuclear complexes showed that, upon photoexcitation in the 200-550 nm range corresponding to the intraligand pi ->pi* transition of the Schiff base, strong and characteristic NIR luminescence of Ln(3+) ions with emissive lifetimes in the microsecond ranges were observed, whereas the ligand-centered singlet ((LC)-L-1) visible fluorescence was mostly quenched as a result of effective intramolecular energy transfer from the (LC)-L-1 excited state to the Ln(3+) ions. In addition, the occupation of py groups at the axial position of Zn2+ ions and the involvement of heavy atoms seem to help to enhance the NIR luminescence to some extent.
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