Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Mansfield Road, Oxford, OX1 3TA, UK.
Chemistry. 2013 Jul 29;19(31):10370-7. doi: 10.1002/chem.201300609. Epub 2013 Jun 20.
Herein, the synthesis and properties of alkyne-bridged carbocations, which are analogous in structure to cyanine dyes, are reported. An alkene-bridged dye, linked at the third position of the indole, was also synthesized as a reference compound. These new carbocations are stable under ambient conditions, allowing characterization by UV/Vis and NMR ((1)H and (13)C) spectroscopies. These techniques revealed a large degree of delocalization of the positive charge, similar to a previously reported porphyrin carbocation. The linear and nonlinear optical properties are compared with cyanine dyes and triarylmethyl cations, to investigate the effects of the bond-length alternation and the overall molecular geometry. The value of Re(γ), the real part of the third-order microscopic polarizability, of -1.3×10(-33) esu for the alkyne-linked cation is comparable to that of a cyanine dye of similar length. Nondegenerate two-photon absorption spectra showed that the alkene-bridged dye exhibited characteristics of cyanines, whereas the alkyne-bridged dye is reminiscent of octupolar chromophores, such as the triarylmethyl carbocation brilliant green. Such attributes were confirmed and rationalized by quantum chemical calculations.
本文报道了炔键桥联碳正离子的合成及性质，其结构类似于花菁染料。还合成了一个作为参考化合物的双键桥联染料，连接在吲哚的第三个位置。这些新的碳正离子在环境条件下稳定，允许通过紫外/可见和 NMR（（1）H 和（13）C）光谱进行表征。这些技术揭示了正电荷的高度离域，类似于以前报道的卟啉碳正离子。通过与花菁染料和三芳基甲基阳离子进行比较，研究了键长交替和整体分子几何形状对线性和非线性光学性质的影响。炔键桥联阳离子的 Re(γ)值（三阶微观极化率的实部）为-1.3×10(-33) esu，与类似长度的花菁染料相当。非简并双光子吸收光谱表明，烯烃桥联染料表现出花菁的特征，而炔键桥联染料类似于八极发色团，如三芳基甲基碳正离子亮绿。这些属性通过量子化学计算得到了证实和合理化。
