School of Mathematics and Physics and Centre for Organic Photonics and Electronics, The University of Queensland, Brisbane, QLD 4072, Australia.
J Chem Phys. 2011 Mar 21;134(11):114520. doi: 10.1063/1.3563801.
We derive structure-property relationships for methine ("Brooker") dyes relating the color of the dye and its symmetric parents to its bond alternation in the ground state and also to the dipole properties associated with its low-lying charge-resonance (or charge-transfer) transition. We calibrate and test these relationships on an array of different protonation states of the green fluorescent protein chromophore motif (an asymmetric halochromic methine dye) and its symmetric parent dyes. The relationships rely on the assumption that the diabatic states that define the Platt model for methine dye color [J. R. Platt, J. Chem. Phys. 25, 80 (1956)] can also be distinguished by their single-double bond alternation and by their charge localization character. These assumptions are independent of the primary constraint that defines the diabatic states in the Platt model--specifically, the Brooker deviation rule for methine dyes [L. G. S. Brooker, Rev. Mod. Phys. 14, 275 (1942)]. Taking these assumptions, we show that the Platt model offers an alternate route to known structure-property relationships between the bond length alternation and the quadratic nonlinear polarizability β. We show also that the Platt model can be parameterized without the need for synthesis of the symmetric parents of a given dye, using the dipole data obtained through spectroscopic measurements. This suggests that the Platt model parameters may be used as independent variables in free-energy relationships for chromophores whose symmetric parents cannot be synthesized or chromophores strongly bound to biomolecular environments. The latter category includes several recently characterized biomolecular probe constructs. We illustrate these concepts by an analysis of previously reported electroabsorption and second-harmonic generation experiments on green fluorescent proteins.
我们推导出了亚甲（“布鲁克”）染料的结构-性质关系，将染料的颜色与其对称母体的颜色与其基态中的键交替以及与其低能电荷共振（或电荷转移）跃迁相关的偶极性质联系起来。我们在一系列不同质子化状态的绿色荧光蛋白发色团 motif（不对称卤代亚甲染料）及其对称母体染料上校准和测试了这些关系。这些关系依赖于这样的假设，即定义 Platt 模型中亚甲染料颜色的非绝热态[J. R. Platt, J. Chem. Phys. 25, 80 (1956)]也可以通过它们的单双键交替和电荷定位特征来区分。这些假设独立于定义 Platt 模型中非绝热态的主要约束条件——具体来说，是亚甲染料的布鲁克偏差规则[L. G. S. Brooker, Rev. Mod. Phys. 14, 275 (1942)]。考虑到这些假设，我们表明 Platt 模型为键长交替与二次非线性极化率β之间的已知结构-性质关系提供了另一种途径。我们还表明，可以使用通过光谱测量获得的偶极数据，在无需合成给定染料的对称母体的情况下，对 Platt 模型进行参数化。这表明 Platt 模型参数可以用作不能合成对称母体的发色团或与生物分子环境强烈结合的发色团的自由能关系中的独立变量。后者包括几个最近表征的生物分子探针结构。我们通过对绿色荧光蛋白的先前报道的电吸收和二次谐波产生实验的分析说明了这些概念。
