Precise control of chirality transfer by adjusting the alkyl substituents of guests

Chirality transfer has been investigated with an m-phthalic diamide-linked zinc bisporphyrinate as host and chiral monoalcohols with different alkyl substituents as guests. The substituent of the guest alcohol had a significant effect on chirality transfer. An increase in the number of carbon atoms from one to three resulted in circular dichroism (CD) sign inversion for the corresponding host-guest complexes. The crystal structures of these zinc bisporphyrinate-monoalcohol complexes revealed two types of orientation for the phenyl ring of the guests: one with the phenyl ring facing the porphyrin plane, and the other with the phenyl ring towards the linker. The chirality transfer mechanism was further studied by DFT and revealed that adjusting the chain length of the alkyl substituent could control the steric interaction between the alkyl group and the porphyrin plane, resulting in different chirality transfer outcomes.