Computational refinement of the puzzling red tetrasulfur chromophore in ultramarine pigments,Physical Chemistry Chemical Physics

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Computational refinement of the puzzling red tetrasulfur chromophore in ultramarine pigments
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2020-09-15 , DOI: 10.1039/d0cp03019h
Paweł Rejmak _{1,

2,

3}

Affiliation

We investigated the cryptic red chromophore, accompanying the blue S₃˙⁻ radical in ultramarine pigments, which usually was tentatively assigned to an unspecified isomer of either neutral S₄ or ionic S₄˙⁻ species. To reveal its identity, we performed the first systematic density functional studies on periodic and large cluster models of red ultramarines, considering several S₄/S₄˙⁻ isomers embedded in aluminosilicate cages. For both neutral and charged tetrasulfides the most stable confined isomer is the planar C_2v one. The only plausible candidate for the red chromophore among the tetrasulfur species is the planar C_2v isomer of the neutral S₄ molecule, which, apart from being thermodynamically preferable, strongly absorbs green light and its vibrational modes match very well with the available Raman data. The C_2v-S₄˙⁻ radical, if present at all in red ultramarines, could be identified by strong absorption in the near infrared region and possibly by the slightly larger isotropic value of the g tensor than that of the S₃˙⁻ radical.

中文翻译：

群青颜料中令人费解的红色四硫发色团的计算精细化

我们研究了隐蔽红色发色团，伴随着蓝S- ₃ ˙ ^-在群青颜料，其通常被暂时分配到中性S的未指定的异构体基团₄或离子小号₄ ˙ ^-物种。为了揭示其身份，我们进行了一次系统地密度泛函研究上的红色群青定期和大型集群模式，考虑到几微秒₄ / S _4分˙ ^-镶嵌在铝笼异构体。对于中性和带电荷的四硫化物，最稳定的受限异构体是平面C _2v一。在四硫物质中，唯一可能的红色生色团是中性S ₄分子的平面C _2v异构体，除了在热力学上是优选的，它还强烈吸收绿光，并且其振动模式与可用的拉曼数据非常吻合。所述Ç _2V -S ₄ ˙ ^-基团，如果存在的话为红色群青，可通过强吸收在近红外区域和可能通过的稍大各向同性值标识克张量小于S的₃ ˙ ^-自由基。

更新日期：2020-10-16

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