Dipartimento di Chimica, Università di Perugia, Via Elce di Sotto, 8, 06123, Perugia, Italy.
Photochem Photobiol Sci. 2011 Jul;10(7):1249-54. doi: 10.1039/c1pp05039g. Epub 2011 May 6.
The present study was undertaken to investigate the photophysical properties of the organic-metal compounds which are the main components of madder lake, one of the most commonly used and widespread organic pigments in painted artworks, from both geographic and historic points of view. Alizarin- and purpurin-Al(III) complexes were studied in solution and as powders. In solution, the chelate stoichiometry, their absorption and emission properties and the efficiency of their excited electronic state deactivation pathways have been determined. The two organic-metal compounds show relevant differences in terms of spectral features consisting of multiple peak (structured) absorption and emission spectra for the purpurin derivative and single broad bands (structureless) for the Al(III)-alizarin chelate. For both the investigated molecules, the chelation process induces a relevant increase of the emission quantum yields and lifetimes. The main differences between photophysical properties of the two metal complexes concern emission quantum yield and lifetime, which are both higher for purpurin chelate compared to alizarine chelate. Furthermore, interesting differences between the two metal complexes concerning the relative relevance of inter- and intra-molecular interaction involved in the mechanism of the excitation energy dissipation have been also highlighted. The knowledge of the determined parameters allows better understanding of the spectral behaviour in the solid state, thus providing a solid reference for the non-invasive characterisation and identification of madder lake on original artworks through its absorption and emission features.
本研究旨在从地理和历史的角度研究胭脂红和茜素-Pur(III) 配合物的光物理性质。胭脂红和茜素-Pur(III) 配合物在溶液中和粉末状态下都进行了研究。在溶液中，确定了螯合物化学计量、它们的吸收和发射性质以及它们激发电子态失活途径的效率。两种有机金属化合物在光谱特征方面表现出明显的差异，包括 purpurin 衍生物的多峰（结构化）吸收和发射光谱以及 Al(III)-alizarin 配合物的单宽带（无结构）。对于这两种研究的分子，螯合过程会导致发射量子产率和寿命的显著增加。两个金属配合物的光物理性质的主要区别在于发射量子产率和寿命，与 alizarine 配合物相比，purpurin 配合物的这两个参数都更高。此外，还强调了两个金属配合物之间关于激发能量耗散机制中涉及的分子内和分子间相互作用的相对重要性的有趣差异。所确定参数的知识允许更好地理解固态中的光谱行为，从而为通过其吸收和发射特性对原始艺术品上的胭脂红进行非侵入性特征描述和鉴定提供了可靠的参考。
