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 (glum=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 (glum=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.

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

ZINNA, FRANCESCO;GUIDO, Ciro Achille;DI BARI, LORENZO;PESCITELLI, GENNARO
Ultimo
2016

Abstract

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 (glum=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 (glum=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.
Zinna, Francesco; Bruhn, Torsten; Guido, Ciro Achille; Ahrens, Johannes; Bröring, Martin; DI BARI, Lorenzo; Pescitelli, Gennaro
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/815921
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