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首页> 外文期刊>RSC Advances >Charge transfer or biradicaloid character: assessing TD-DFT and SAC-CI for squarylium dye derivatives
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Charge transfer or biradicaloid character: assessing TD-DFT and SAC-CI for squarylium dye derivatives

机译：电荷转移或双自由基特性：评估TD-DFT和SAC-CI用于方酸染料衍生物

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摘要

Keeping in view to suggest one more class of molecules in order to make a choice and assessment of exchange-correlation (XC) functionals, symmetrical squarylium dye (SQ) derivatives have been considered and Le Bahers's diagnostic indexes have been applied to study the electronic transition character of these molecular systems through TD-DFT and SAC-CI methods. Unlike calculated absorption using SAC-CI, the TD-DFT results do not match with experimental absorption data. However, the diagnostic indexes obtained with TD-DFT and SAC-CI are apparently similar for all methods. This indicates that care should be taken while choosing XC functionals and assessing the nature of electronic transitions of a specific class of molecules. The centroids of charges associated with the density increase and depletion regions are localized on the central C4 ring and carbonyl groups and with a small extension up to side aromatic substitution of the SQ dye derivative. Hence, the electronic transition occurring in this class of molecules is confined mainly within the central part of molecule. This is in contrast to donor-acceptor-donor type structure in which the charge depletion region is expected at side aromatic substitution of the molecule. The small values of calculated transferred charge (q(CT)) upon excitation lend support to the theory that the electronic transition in this class of molecules is not CT excitation. This is in agreement with our earlier finding that biradicaloid character and orbital interactions play a key role in their NIR absorption. Hence, highly correlated, single reference and a multideterminant SAC-CI method is able to explain the nature of electronic excitations in these molecules rather than TD-DFT with various types of XC functionals.
机译：为了提出更多一类分子以选择和评估交换相关（XC）功能，我们考虑了对称方酸染料（SQ）衍生物，并将Le Bahers的诊断指标用于研究电子跃迁TD-DFT和SAC-CI方法鉴定这些分子系统的特征。与使用SAC-CI计算的吸收不同，TD-DFT结果与实验吸收数据不匹配。但是，对于所有方法，用TD-DFT和SAC-CI获得的诊断指标显然相似。这表明在选择XC功能并评估特定类别分子的电子跃迁的性质时应格外小心。与密度增加和耗尽区相关的电荷质心位于中央C4环和羰基上，并且延伸很小，直至SQ染料衍生物的侧芳取代。因此，发生在这类分子中的电子跃迁主要限于分子的中心部分。这与供体-受体-供体类型的结构相反，在该结构中，预期在分子的侧芳取代处具有电荷耗尽区。激发时计算出的转移电荷（q（CT））的较小值支持以下理论：此类分子中的电子跃迁不是CT激发。这与我们先前的发现一致，即双自由基性质和轨道相互作用在其近红外吸收中起关键作用。因此，高度相关的单一参考和多决定因素SAC-CI方法能够解释这些分子中电子激发的性质，而不是具有各种XC功能的TD-DFT。

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