Circularly Polarized Luminescence from Axially Chiral BODIPY DYEmers: An Experimental and Computational Study

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• 作者：Francesco Zinna ; Dr. Torsten Bruhn ; Dr. Ciro A. Guido ; Dr. Johannes Ahrens ; Prof. Martin Brö ; ring ; Prof. Lorenzo Di Bari and Prof. Gennaro Pescitelli
• 刊名：Chemistry - A European Journal
• 出版年：2016
• 出版时间：November 2, 2016
• 年：2016
• 卷：22
• 期：45
• 页码：16089-16098
• 全文大小：1318K
• ISSN：1521-3765

文摘

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_lum=4×10⁻³) 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_lum=4×10⁻⁴), 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.