Control of Circularly Polarized Luminescence by Orientation of Stacked π‐Electron Systems

Abstract

Planar chiral buildingb locks based on 4,7,12,15tetrasubstituted [2.2]paracyclophanes were obtained via a synthetic route involving an optical resolutions tep. Planar chiral enantiomers, comprising two fluorophores that were stacked to form aV -shaped higher-ordered structure, were synthesized from these building blocks. The Vshaped molecules emitted intensec ircularly polarizedl uminescence (CPL). Their chiroptical properties were compared with those of X-shaped molecules bearing the same two fluorophores stacked together.T he CPL sign of the Xshaped molecule was opposite to that of the V-shaped molecule, which is supported by the theoretical results, indicating that the CPL sign can be controlled by the orientation of the stacked fluorophores.

Control of Axial Chirality by Planar Chirality Based on Optically Active [2.2]Paracyclophane

“…Such inflexibility allows control of the orientation of the stacked π‐electron systems. Indeed, we previously prepared various optically active π‐stacked molecules using enantiopure [2.2]paracyclophanes as chiral building blocks, [4a] whereby the orientation of the π‐electron systems was controlled to allow the construction of optically active second‐ordered structures, such as V‐, [4b,c] X‐, [4d,e] †‐, [4f] double helical, [4g] and two‐blades‐propeller‐shaped structures, [4h] resulting in the excellent circularly polarized luminescence (CPL) emission [5, 6]…”

Beyond Simple Substitution Patterns – Symmetrically Tetrasubstituted [2.2]Paracyclophanes as 3D Functional Materials

“…Another recent example of an X‐shaped PC derivative synthesized as pure enantiomer is 62 (Scheme ), acting as model compound for two terminally methoxy functionalized OPE rods with stacked central phenyl units. The chiroptical properties of X‐shaped 62 were compared with its V‐shaped structural isomer 63 (Scheme ), with stacking terminal phenyl subunits . Also 63 was synthesized as pure enantiomer and the access of pure enantiomers of the PC building block will be discussed in the following chapter 4 ( 80 in Scheme ).…”

“…Comparison of the CPL features of the X‐ and V‐shaped model compounds 62 and 63 displayed opposite CPL signs with respect to the chirality of their CP subunit. The authors thus identified the spatial orientation of both OPE rods as more important for their chiroptical properties than their absolute configuration …”

“…Synthesis of the series of chiral CP comprising dendrimers 57 and the X‐shaped molecules 58 and 59 for aggregation studies, the extended model compounds 60 and 61 , which were analyzed as CPL emitters, and the V‐shaped model compound 63 …”

“…A variation of the optical resolution procedure giving access to the enantiopure building blocks ( R p )‐ 80 and ( S p )‐ 80 has been reported recently by the same group . The pairs of diastereomers 77 was first doubly brominated and subsequently separated by crystallization and silica gel chromatography, making both diastereomers ( R p ,1 S ,4 R )‐ 79a and ( S p ,1 S ,4 R )‐ 79b available in gram scale.…”