title: Circularly Polarized Luminescence from Axially Chiral BODIPY DYEmers: An Experimental and Computational Study.
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.
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Moruzzi 13, 56124, Pisa, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Zinna
authors.affiliation: Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Torsten
authors.identifier: http://orcid.org/0000-0002-9604-1004
authors.initials: T
authors.lastname: Bruhn
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Moruzzi 13, 56124, Pisa, Italy.
authors.forename: Ciro A
authors.identifier: http://orcid.org/0000-0003-1924-2862
authors.initials: CA
authors.lastname: Guido
authors.affiliation: Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106, Braunschweig, Germany.|Department of Organic Chemistry, Weizmann Institute of Science, 76100, Rehovot, Israel.
authors.forename: Johannes
authors.identifier: http://orcid.org/0000-0002-4927-6273
authors.initials: J
authors.lastname: Ahrens
authors.affiliation: Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106, Braunschweig, Germany.
authors.forename: Martin
authors.identifier: http://orcid.org/0000-0001-6807-6579
authors.initials: M
authors.lastname: Bröring
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Moruzzi 13, 56124, Pisa, Italy. lorenzo.dibari@unipi.it.
authors.forename: Lorenzo
authors.identifier: http://orcid.org/0000-0003-2347-2150
authors.initials: L
authors.lastname: Di Bari
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Moruzzi 13, 56124, Pisa, Italy. gennaro.pescitelli@unipi.it.
authors.forename: Gennaro
authors.identifier: http://orcid.org/0000-0002-0869-5076
authors.initials: G
authors.lastname: Pescitelli
keywords: atropisomeric biaryls; boron dipyrrin; chiroptical spectroscopy; density functional calculations; luminescence