Deciphering the circularly polarized luminescence of covalent organic frameworks (COFs) through ab initio modelling

Abstract

Chirality is a radical property largely observed in the universe, arising in objects lacking inversion symmetry, thereby making the objects exist as entities with distinct handedness. After proper interference with asymmetric radiation, such forms can potentially emit chiral light with an excess of right- or left-handed circular polarization, reporting events of circularly polarized luminescence. Recent developments in reticulated nanomaterials, such as covalent organic frameworks, have shown chiroptical responses that far exceed those found in their isolated monomers. However, these recent advances still lack a solid computational foundation for proper interpretation of chiroptical phenomena. The present contribution, through robust yet accessible ab initio theoretical treatment, aimed at precisely decoding the unique CPL spectral features that arise in COFs presenting different types of chirality (stereogenic, axial and intrinsic). A multilevel approach combining DFT benchmark, excited Born–Oppenheimer molecular dynamics and TD-DTF analyses clarified how the effects of dimensionality, reticulation and chirality transfer through bond/space can influence the CPL bands of COFs. Lastly, it was demonstrated that a small set of exchange–correlation functionals (M11L, O3LYP and ωB97xD) is valid for simulating the CPL spectra of all the chiral-emissive pure COFs reported in the literature to date. These results can play a constructive role in the future design of high-performance CPL COFs, stimulating new opportunities for research on chiral luminescent bidimensional architectures.