Görner Helmut, Khanra Sumit, Weyhermüller Thomas, Chaudhuri Phalguni
Max-Planck-Institut für Bioanorganische Chemie, D-45413 Mülheim an der Ruhr, Germany.
J Phys Chem A. 2006 Mar 2;110(8):2587-94. doi: 10.1021/jp053662p.
N,N'-Bis(salicylidene)hydrazine (L(I)), a bis-2-hydroxybenzene-type ligand H2L, its tert-butyl derivative (L(II)), and the corresponding Zn2+ complexes of the type Zn2(LH)2L (Zn-I and Zn-II) were synthesized. The molecular structure of Zn-II was determined by X-ray crystallography at -170 degrees C. The photoreactions of the four compounds in solution were studied by time-resolved UV-vis spectroscopy using nanosecond laser pulses. A weak but strongly Stokes shifted fluorescence signal of the ligands L(I) or L(II) is suggested to be due to excited-state intramolecular proton transfer (ESIPT) from the phenolic hydroxy group to the nitrogen of the methine bond in analogy to the fast enol --> keto tautomerization of other 2-hydroxybenzenes. A transient with the maximum at 480 nm, bleaching at 370 nm, and a lifetime of 0.01-0.3 ms is attributed to the trans-keto tautomer, formed via internal conversion. The decay occurs via trans --> cis isomerization and proton back-transfer to the enol form. Quenching by water indicates a proton-catalyzed reaction. To account for similar fluorescence and transient properties in the cases of the Zn2+ complexes, a photoinduced tautomerism at one of the two free phenolic hydroxy groups is proposed. The rapid ESIPT followed by a relatively slow relaxation process is reversible.
合成了N,N'-双（水杨醛）肼（L(I)），一种双-2-羟基苯型配体H2L，其叔丁基衍生物（L(II)），以及Zn2(LH)2L型的相应锌配合物（Zn-I和Zn-II）。通过在-170℃下的X射线晶体学确定了Zn-II的分子结构。使用纳秒激光脉冲，通过时间分辨紫外可见光谱研究了这四种化合物在溶液中的光反应。配体L(I)或L(II)的微弱但斯托克斯位移强烈的荧光信号被认为是由于激发态分子内质子转移（ESIPT），即从酚羟基转移到次甲基键的氮上，类似于其他2-羟基苯的快速烯醇→酮互变异构。在480nm处有最大值、在370nm处有漂白且寿命为0.01 - 0.3ms的瞬态归因于通过内转换形成的反式酮互变异构体。衰变通过反式→顺式异构化和质子回转移到烯醇形式发生。水猝灭表明是质子催化反应。为了解释锌配合物情况下类似的荧光和瞬态性质，提出了在两个游离酚羟基之一处的光诱导互变异构。快速的ESIPT之后是相对缓慢的弛豫过程，这是可逆的。
