Evidence for excited state intramolecular charge transfer in benzazole-based pseudo-stilbenes.
Evidence for excited state intramolecular charge transfer in benzazole-based pseudo-stilbenes.
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基于苯并唑的假茋中激发态分子内电荷转移的证据。
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
F. Rodembusch
中科院分区：
文献类型：
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作者：
F. S. Santos;R. R. Descalzo;P. Gonçalves;E. Benvenutti;F. Rodembusch
以黏土蒙脱土KSF为催化剂，通过氨基苯并唑衍生物与N，N-二甲基苯胺的重氮化反应，得到了两个偶氮化合物。采用元素分析、傅里叶变换红外光谱、（13）C和(1)H核磁共振光谱对合成的染料进行了表征。用紫外-可见和稳态荧光法研究了它们的光物理行为。这些染料在蓝色区域表现出强烈的吸收。偶氮化合物的光谱特征可能与染料的伪二苯乙烯类型和E异构体有关。在吸收最大值处的激发不会产生激发态的发射物质。然而，在350 nm左右的激发允许荧光从局部激发（LE，短波长）和分子内电荷转移（ICT，长波长）状态双重发射，荧光最大值（ν(max)）与溶剂极性函数（Δf）的线性关系证实了这一点。从ICT发射波段荧光强度的黏度依赖性出发，讨论了这些染料中存在TICT的证据。为了研究染料在基态和激发态的几何形状和电荷分布，还进行了理论计算。利用理论能级BLYP/ augc -cc- pvdz进行几何优化和频率计算，B3LYP/6-311+G（2d）进行单点能量评估，计算结果表明，能量最低和最强烈的光子吸收导致极激发态非放射性松弛，这可能与光化学异构化有关。
Two azo compounds were obtained through the diazotization reaction of aminobenzazole derivatives and N,N-dimethylaniline using clay montmorillonite KSF as catalyst. The synthesized dyes were characterized using elemental analysis, Fourier transform infrared spectroscopy, and (13)C and (1)H NMR spectroscopy in solution. Their photophysical behavior was studied using UV-vis and steady-state fluorescence in solution. These dyes present intense absorption in the blue region. The spectral features of the azo compounds can be related to the pseudo-stilbene type as well as the E isomer of the dyes. Excitation at the absorption maxima does not produce emissive species in the excited state. However, excitation around 350 nm allowed dual emission of fluorescence, from both a locally excited (LE, short wavelength) and an intramolecular charge transfer (ICT, long wavelength) state, which was corroborated by a linear relation of the fluorescence maximum (ν(max)) versus the solvent polarity function (Δf) from the Lippert-Mataga correlation. Evidence of TICT in these dyes was discussed from the viscosity dependence of the fluorescence intensity in the ICT emission band. Theoretical calculations were also performed in order to study the geometry and charge distribution of the dyes in their ground and excited electronic states. Using DFT methods at the theoretical levels BLYP/Aug-cc-pVDZ, for geometry optimizations and frequency calculations, and B3LYP/6-311+G(2d), for single-point energy evaluations, the calculations revealed that the least energetic and most intense photon absorption leads to a very polar excited state that relaxes non-radioactively, which can be associated with photochemical isomerization.