Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
Phys Chem Chem Phys. 2011 Sep 7;13(33):15022-30. doi: 10.1039/c1cp21380f. Epub 2011 Jul 14.
In this work, we substantiate the change in the emitting state of indole caused by the dipolarity increase in the solvent 1-chlorobutane, observed on lowering the temperature from 293 to 133 K, accompanied by no significant changes in the corresponding excitation and absorption spectra. No similar changes in indole emission were observed over the temperature range 293-133 K for solutions of indole in 2-methylbutane in the presence and absence of 0.5 M 1-chlorobutane. The solvatochromism of indole in 1-chlorobutane at temperatures from 293 to 133 K allowed us to estimate the dipole moment and polarizability of the emission state of the chromophore and to detect two states (S(1) and ): one, the S(1), involving no significant change and the other, the , exhibiting a substantial change in the dipole moment of the chromophore upon electronic excitation (viz. μ(S(1)) = 2.5 and vs. μ(S(0)) = 2.13 D). The former state, S(1), is the major contributor to the structured emission of indole at temperatures from 293 to 193 K, as is the latter, S'(1) , to its structureless, red-shifted emission over the range 193-133 K. Although the emission changes of indole, dissolved in 1-chlorobutane at temperatures from 293 to 133 K, are seemingly consistent with the widely accepted photophysical model for inversion of its (1)L(b) and (1)L(a) states as the polarity of the medium is increased, below 133 K the emission becomes structured and blue-shifted, two typical features of indole above 193 K. Also, below 123 K is not feasible to photo-select the (1)L(a) state in spite of this state being the first excited electronic state of indole under large dipolarity conditions. Therefore, the established photophysical model cannot hold under these conditions and a new one accounting for these experimental facts is proposed instead.
在这项工作中，我们证实了吲哚在溶剂 1-氯丁烷中偶极矩增加导致的发射态变化，这种变化是在温度从 293 降至 133 K 时观察到的，同时相应的激发和吸收光谱没有显著变化。在 293-133 K 的温度范围内，对于吲哚在 2-甲基丁烷中的溶液，无论是否存在 0.5 M 1-氯丁烷，都没有观察到吲哚发射的类似变化。吲哚在 1-氯丁烷中的溶剂化变色，在 293-133 K 的温度范围内，使我们能够估计发色团发射态的偶极矩和极化率，并检测到两种状态（S(1)和 S(0)）：一种是 S(1)，没有明显变化，另一种是 S(0)，在电子激发时，发色团的偶极矩发生显著变化（即 μ(S(1))=2.5 和 vs. μ(S(0))=2.13 D）。前者状态 S(1)，是吲哚在 293-193 K 温度范围内结构发射的主要贡献者，后者状态 S'(1)，是其在 193-133 K 温度范围内无结构、红移发射的主要贡献者。尽管吲哚在 1-氯丁烷中的溶解，在 293-133 K 的温度范围内的发射变化，似乎与广泛接受的其（1）L(b)和（1）L(a）态反转的光物理模型一致，但在 133 K 以下，发射变得结构和蓝移，这是吲哚在 193 K 以上的两个典型特征。此外，尽管在大偶极矩条件下，（1）L(a）态是吲哚的第一激发电子态，但在 123 K 以下，仍然无法对其进行光选择。因此，在这些条件下，所建立的光物理模型不再适用，取而代之的是提出了一个新的模型，该模型考虑了这些实验事实。
