Laboratory for Computational Molecular Design, Institute of Chemical Sciences and Engineering, Ecole Polytechnique federale de Lausanne (EPFL), 1015 Lausanne, Switzerland.
Phys Chem Chem Phys. 2023 Jun 7;25(22):15200-15208. doi: 10.1039/d3cp01343j.
Electrohelicity arises in molecules such as allene and spiropentadiene when their symmetry is reduced and helical frontier molecular orbitals (MOs) appear. Such molecules are optically active and electrohelicity has been suggested as a possible design principle for increasing the chiroptical response. Here we examine the fundamental link between electrohelicity and optical activity by studying the origin of the electric and magnetic transition dipole moments of the π-π* transitions. We show that the helical character of the MOs drives the optical activity in allene, and we use this knowledge to design allenic molecules with increased chiroptical response. We further examine longer carbyne-like molecules. While the MO helicity also contributes to the optical activity in non-planar butatriene, the simplest cumulene, we show there is no relation between the chiroptical response and the helical π-MOs of tolane, a simple polyyne. Finally, we demonstrate that the optical activity of spiropentadiene is inherently linked to mixing of its two π-systems rather than the helical shape of its occupied π-MOs. We thus find that the fundamental connection between electrohelicity and optical activity is very molecule dependent. Although electrohelicity is not the underlying principle, we show that the chiroptical response can be enhanced through insight into the helical nature of electronic transitions.
电螺旋光活性出现在具有对称减少和螺旋前线分子轨道（MOs）的化合物中，如丙二烯和螺戊二烯。这些分子具有光学活性，电螺旋光活性被认为是增加手性光学响应的可能设计原则。在这里，我们通过研究π-π*跃迁的电和磁跃迁偶极子的起源，研究了电螺旋光活性和光学活性之间的基本联系。我们表明，MO 的螺旋特征驱动了丙二烯的光学活性，并且我们利用这一知识设计了具有增强手性光学响应的丙二烯分子。我们进一步研究了更长的类碳炔分子。虽然 MO 的螺旋性也对非平面但二烯（最简单的累积烯）的光学活性有贡献，但我们表明，在手性光学响应与螺烯（一种简单的多炔）的占据π-MOs 的螺旋形状之间没有关系。最后，我们证明了螺戊二烯的光学活性与其两个π系统的混合有关，而与其占据的π-MOs 的螺旋形状无关。因此，我们发现电螺旋光活性和光学活性之间的基本联系非常依赖于分子。尽管电螺旋光活性不是基础原理，但我们表明，通过深入了解电子跃迁的螺旋性质，可以增强手性光学响应。
