Zinna Francesco, Bruhn Torsten, Guido Ciro A, Ahrens Johannes, Bröring Martin, Di Bari Lorenzo, Pescitelli Gennaro
Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Moruzzi 13, 56124, Pisa, Italy.
Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
Chemistry. 2016 Nov 2;22(45):16089-16098. doi: 10.1002/chem.201602684. Epub 2016 Sep 23.
With our new home-built circularly polarized luminescence (CPL) instrument, we measured fluorescence and CPL spectra of the enantiomeric pairs of two quasi-isomeric BODIPY DYEmers 1 and 2, endowed with axial chirality. The electronic circular dichroism (ECD) and CPL spectra of these atropisomeric dimers are dominated by the exciton coupling between the main π-π* transitions (550-560 nm) of the two BODIPY rings. Compound 1 has strong ECD and CPL spectra (g =4×10 ) well reproduced by TD-DFT and SCS-CC2 (spin-component scaled second-order approximate coupled-cluster) calculations using DFT-optimized ground- and excited-state structures. Compound 2 has weaker ECD and CPL spectra (g =4×10 ), partly due to the mutual cancellation of electric-electric and electric-magnetic exciton couplings, and partly to its conformational freedom. This compound is computationally very challenging. Starting from the optimized excited-state geometries, we predicted the wrong sign for the CPL band of 2 using TD-DFT with the most recommended hybrid and range-separated functionals, whereas SCS-CC2 or a DFT functional with full exact exchange provided the correct sign.
利用我们新自制的圆偏振发光（CPL）仪器，我们测量了两种具有轴手性的准异构体BODIPY DYEmers 1和2的对映体对的荧光和CPL光谱。这些阻转异构二聚体的电子圆二色性（ECD）和CPL光谱主要由两个BODIPY环的主要π-π*跃迁（550 - 560 nm）之间的激子耦合主导。化合物1具有很强的ECD和CPL光谱（g = 4×10），使用DFT优化的基态和激发态结构通过TD-DFT和SCS-CC2（自旋分量缩放二阶近似耦合簇）计算能很好地重现。化合物2的ECD和CPL光谱较弱（g = 4×10），部分原因是电-电和电-磁激子耦合的相互抵消，部分原因是其构象自由度。该化合物在计算上极具挑战性。从优化的激发态几何结构出发，我们使用最推荐的杂化和范围分离泛函的TD-DFT预测了化合物2的CPL带的错误符号，而SCS-CC2或具有完全精确交换的DFT泛函给出了正确的符号。
