First-principles modelling of circularly polarized luminescence in one-handed helical ladder polymers

Abstract

The idea of helical chirality bridges the gap between stereogenic asymmetry at the local scale and intrinsic non-superimposability in larger secondary structures (DNA, RNA, α-helix protein, etc.). Novel synthetic breakthroughs allowed the ascent of a brand-new subclass of chiral materials based on defect-free single-handed helical ladder polymers, reducing the conceptual barrier between small artificial helical foldamers and helical biomacromolecules. Beyond their extraordinary physicochemical properties, the interference of circularly polarized radiation with optically pure one-handed helical ladder polymers paved the way for pronounced circularly polarized luminescence events. This work, through a systematic theoretical investigation, tackled the CPL spectral profiles of a multitude of enantiomeric ladder-type polymers with diversified helical arrangements and topological cavities. The computational protocol integrated a preliminary ground state treatment of chiral monomeric units with excited-state molecular dynamics of oligomeric and polymeric systems to understand how key geometrical parameters of ladderization precursors vary upon photoexcitation for chemical architectures of increasing size. The consolidation of APFD and O3LYP functionals performances, through the rigorous assessment of chiroptical descriptors (emission energies, rotational strengths, electric/magnetic transition dipole moments and their angle), allowed us to evaluate how the chiral dimensionality orients the CPL spectra of one-handed helical ladder polymers in terms of peak position, band shape, chiral sign and signal magnitude.