Freytag Emely, Kreimendahl Lasse, Holzapfel Marco, Petersen Jens, Lackinger Heiko, Stolte Matthias, Würthner Frank, Mitric Roland, Lambert Christoph
Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
J Org Chem. 2023 Aug 4;88(15):10777-10788. doi: 10.1021/acs.joc.3c00821. Epub 2023 Jul 24.
Five chiral squaraine dimers were synthesized by fusing chiral indolenine semisquaraines with three different benzobisthiazole bridges. The thereby created squaraine dimers show a strong splitting of the lowest energy absorption bands caused by exciton coupling. The intensities of the two exciton transitions and the energetic splitting depend on the angle of the two squaraine moieties within the chromophore dimer. The electric circular dichroism spectra of the dimers show intense Cotton effects whose sign depends on the used squaraine chromophores. Sizable anisotropies of up to 2.6 × 10 could be obtained. TD-DFT calculations were used to partition the rotational strength into the three Rosenfeld terms where the electric-magnetic coupling turned out to be the dominant contribution while the exciton chirality term is much smaller. This is because the chromophore dimers are essentially planar but the angle between the electric transition dipole moment of one squaraine and the magnetic transition dipole moment of the other squaraine strongly deviates from 90°, which makes the dot product between the two moment vectors and, thus, the rotational strength substantial.
通过将手性吲哚啉半方酸与三种不同的苯并双噻唑桥相连，合成了五种手性方酸二聚体。由此产生的方酸二聚体显示出由激子耦合引起的最低能量吸收带的强烈分裂。两个激子跃迁的强度和能量分裂取决于发色团二聚体内两个方酸部分的角度。二聚体的电圆二色光谱显示出强烈的科顿效应，其符号取决于所使用的方酸发色团。可获得高达2.6×10的可观各向异性。采用TD-DFT计算将旋转强度划分为三个罗森菲尔德项，其中电磁耦合是主要贡献，而激子手性项要小得多。这是因为发色团二聚体基本上是平面的，但一个方酸的电跃迁偶极矩与另一个方酸的磁跃迁偶极矩之间的角度强烈偏离90°，这使得两个矩向量之间的点积以及旋转强度都很大。
