Bending benzenes and twisting light

This doctoral thesis investigates chiral carbon nanohoops which are curved π-conjugated molecules as promising materials for circularly polarized luminescence (CPL) applications in advanced displays, sensors, and optoelectronics. The thesis first introduces the fundamentals of circular dichroism (CD) and CPL spectroscopy and emphasizes key performance metrics such as fluorescence quantum yields and dissymmetry factors of absorption and emission, which quantify how effectively molecules generate circularly polarized light. It also reveals the importance of placing the electric and magnetic transition dipole moments at an optimal angle and explores strategies for developing chiral carbon nanohoops. More broadly, it examines how chirality, symmetry, and molecular strain govern the photophysical and chiroptical properties of these systems.
The first part of the thesis is devoted to investigating the role of exciton delocalization in boosting CD and CPL responses. For this purpose, carbon nanohoops bearing [2.2]paracyclophane (PCP) as a chiral moiety and an acceptor group as a chromophore were synthesized. Although the study reveals desirable photophysical properties with modest dissymmetry factors, it provides key design guidelines for enhancing CPL response. Further work replaces the chiral PCP unit by a [5]helicene to study the role of extended π-conjugation on CPL. A strong correlation between experimental and computational data was observed, validating models for screening future CPL candidates. Further, to study the effect of ring strain on their stereodynamic stability, a series of helicene nanohoops of varying sizes were synthesized and their racemization kinetics were recorded and analyzed. Overall, the thesis delivers structure-property relationships for high performance CPL emitters.