Fluorescence anisotropy spectra disclose the role of disorder in optical spectra of branched intramolecular-charge-transfer molecules.
Fluorescence anisotropy spectra disclose the role of disorder in optical spectra of branched intramolecular-charge-transfer molecules.
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DOI：
10.1021/jp2027274
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发表时间：
2011-05
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影响因子：
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通讯作者：
C. Sissa;A. Painelli;M. Blanchard‐Desce;F. Terenziani
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文献类型：
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作者：
C. Sissa;A. Painelli;M. Blanchard‐Desce;F. Terenziani
报道了分子内电荷转移（ICT）生色团的荧光激发和发射光谱及其各向异性。为了揭示与极性溶剂化有关的无序的作用，我们收集了从不同极性溶剂中获得的玻璃中具有八极（C（3））对称性的分子的光谱。与极性溶剂化有关的热无序表现为荧光激发/发射光谱和各向异性光谱对发射/激发波长的依赖性。特别地，对于吸收带的红色边缘中的激发，荧光各向异性信号偏离八极发色团预期的0.1值，接近极限0.4值。在非极性溶剂中观察到定性不同的结果。ICT发色团的本质状态模型的基础上，我们开发了一个原始的方法来计算各向异性光谱，定量再现实验数据。该模型，占电子和分子振动和极性溶剂化之间的耦合，导致在分支ICT发色团的溶质-溶剂相互作用的基础上的现象的透彻理解。一个明确的区别是在激发态和无序诱导的分子对称性降低的破缺现象。指出了它们与红边效应的关系。
Fluorescence excitation and emission spectra and corresponding anisotropies of branched intramolecular charge-transfer (ICT) chromophores are reported. To unravel the role of disorder related to polar solvation, we collected spectra of molecules with octupolar (C(3)) symmetry in glasses obtained from solvents of different polarity. Thermal disorder related to polar solvation is demonstrated by the dependence of fluorescence excitation/emission spectra and anisotropy spectra on the emission/excitation wavelength. In particular, for excitation in the red edge of the absorption band, the fluorescence anisotropy signal deviates from the 0.1 value expected for octupolar chromophores, approaching the limiting 0.4 value. A qualitatively different result is observed in nonpolar solvents. Based on essential-state models for ICT chromophores, we develop an original approach for the calculation of anisotropy spectra that quantitatively reproduces experimental data. The model, accounting for the coupling between electrons and molecular vibrations and polar solvation, leads to a thorough understanding of the phenomena at the basis of solute-solvent interactions in branched ICT chromophores. A clear distinction is made between symmetry-breaking phenomena in the excited state and disorder-induced lowering of the molecular symmetry. Their relation with red-edge effects is pointed out.