Role of exciton delocalization in chiroptical properties of benzothiadiazole carbon nanohoops.

Development of chiral organic materials with a strong chiroptical response is crucial to advance technologies based on circularly polarized luminescence, enantioselective sensing, or unique optical signatures in anti-counterfeiting. The progress in the field is hampered by the lack of structure-property relationships that would help designing new chiral molecules. Here, we address this challenge by synthesis and investigation of two chiral macrocycles that integrate in their structure a pseudo-meta [2.2]paracyclophane with planar chirality and a highly fluorescent benzothiadiazole. Both compounds display remarkably red-shifted fluorescence with high quantum yields and large Stokes shifts. They differ in the extent of π-electron conjugation that allowed, for the first time, systematic examination of the effect of exciton delocalization on the absorption and luminescence of circularly polarized light. By a combination of steady-state spectroscopy and quantum chemical calculations, we constructed a unique structure-property relationship offering critical insights that will aid and abet the development of robust design guidelines for materials with strong electronic circular dichroism or circularly polarized luminescence of exceptional brightness.