Liu Xiaogang, Cole Jacqueline M, Waddell Paul G, Lin Tze Chia
Cavendish Laboratory, Department of Physics, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, England.
Acta Crystallogr B. 2011 Dec;67(Pt 6):560-8. doi: 10.1107/S0108768111037311. Epub 2011 Oct 13.
The molecular structures of three compounds, LD 425 (C(13)H(14)N(2)O(3)) (1), LD 489 (C(15)H(15)F(3)N(2)O(2)) (2) and LD 473 (C(17)H(19)F(3)N(2)O) (3), are determined by single-crystal X-ray diffraction (XRD) at 180 K. Azacoumarins (1) and (2) possess para-quinoidal bond-length patterns in their benzene rings due to intramolecular charge transfer (ICT) from these rings to the adjoining rings. In contrast, substitution of O with N within the coumarin heterocycle, to form a 2-quinolone, results in the suppression of this ICT effect. Instead, charge transfer within the heterocycle is shown to become more pronounced. Resonance theory is employed to discuss these bond pattern differences and characteristic spectral blue shifts in relation to their coumarin analogues. The application of this theory offers an intuitive understanding of the structure-property relationships in azacoumarins and 2-quinolones which is further supported by quantum chemical calculations. Such an understanding is important for recognizing ICT mechanisms in these compounds which can then be used to facilitate the molecular design of new laser dyes with the desired spectral shifts.
通过在180 K下的单晶X射线衍射（XRD）确定了三种化合物LD 425（C₁₃H₁₄N₂O₃）（1）、LD 489（C₁₅H₁₅F₃N₂O₂）（2）和LD 473（C₁₇H₁₉F₃N₂O）（3）的分子结构。氮杂香豆素（1）和（2）由于分子内电荷转移（ICT）从其苯环转移到相邻环，在其苯环中具有对醌型键长模式。相反，在香豆素杂环内用N取代O以形成2-喹诺酮，导致这种ICT效应受到抑制。取而代之的是，杂环内的电荷转移变得更加明显。采用共振理论来讨论这些键型差异以及与其香豆素类似物相关的特征光谱蓝移。该理论的应用提供了对氮杂香豆素和2-喹诺酮结构-性质关系的直观理解，量子化学计算进一步支持了这一点。这种理解对于认识这些化合物中的ICT机制很重要，然后可用于促进具有所需光谱位移的新型激光染料的分子设计。
