Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
J Phys Chem A. 2012 May 17;116(19):4726-34. doi: 10.1021/jp211330x. Epub 2012 May 3.
The UV/vis absorption and fluorescence spectra of 9,9'-bisanthracenyl (BA), 9,9'- bisacridinyl (BAC), 9,9'-bicarbazyl (BC), and 9-(9'-anthracenyl)carbazole (C9A) were precisely recorded in solvents that change their solvent dipolarity scale (SdP) values from 0.000 (in 2-methylbutane at 293 K) to 1.294 (in 1-chlorobutane at 77 K). An analysis based (i) on the solvatochromic behavior of the four 9,9'-biaryl compounds in terms of the dipolarity of the solvents used, quantified by means of their SdP values, and (ii) on the behavior of the emission band profiles, allows the conclusion that, whereas the apolar 9,9'-biaryl compounds BA, BAC, and BC need solvents with SdP values larger than 0.74 to give a twisted intramolecular charge-transfer (TICT) process after excitation, for dipolar C9A the TICT mechanism is predominant already at solvent SdP values smaller than 0.23, i.e., near a solvent dipolarity of 0. The accuracy and simplicity achieved by application of the SdP scale in analyzing the solvatochromic behavior of the four 9,9'-biaryl compounds studied make evident the advantages of this solvent scale in comparison to other empirical solvent scales, which not only include the solvent's dipolarity but also consist of a more limited numerical range of values only.
9,9'-双蒽基（BA）、9,9'-双吖啶基（BAC）、9,9'-双碳酰肼（BC）和 9-（9'-蒽基）咔唑（C9A）的紫外可见吸收和荧光光谱在溶剂中精确记录，这些溶剂的溶剂偶极矩标度（SdP）值从 0.000（293 K 下的 2-甲基丁烷）变化到 1.294（77 K 下的 1-氯丁烷）。基于（i）四种 9,9'-联芳基化合物在所用溶剂的偶极矩方面的溶剂变色行为，通过它们的 SdP 值进行量化，以及（ii）发射带轮廓的行为，得出结论，非极性 9,9'-联芳基化合物 BA、BAC 和 BC 需要 SdP 值大于 0.74 的溶剂才能在激发后发生扭曲的分子内电荷转移（TICT）过程，而对于偶极 C9A，TICT 机制在 SdP 值小于 0.23 的溶剂中已经占主导地位，即接近 0 的溶剂偶极矩。在分析研究的四种 9,9'-联芳基化合物的溶剂变色行为时应用 SdP 标度达到的准确性和简单性，使得与其他经验溶剂标度相比，这种溶剂标度具有明显的优势，后者不仅包含溶剂的偶极矩，而且还仅包含更有限的数值范围值。
