Impact of Structural Subtleties on Chirality Induction and Amplification in Trizinc(II)Porphyrin Trimers

Abstract

Herein, we report the precise control of molecular to supramolecular chirality induction at the single-molecule level just upon subtle modification in an achiral 'nano-size' trizinc(II) porphyrin trimer. A slight variation in the projection of the substituent at the periphery of the central porphyrin unit in a porphyrin trimer (host) resulted in pronounced changes in the interchromophoric arrangement, leading to distinct 'open' and 'closed' conformations. While 'open' form generates 'monomeric' complex with low CD amplitude, 'closed' form produces exclusive 'polymer' with large, amplified CD signal with opposite sign due to stronger intermolecular excitonic coupling. Also, the sign of the CD couplets is just opposite between R and S substrates for both polymer and monomer which suggest that the chirality is predominantly governed by the stereogenic projection of the chiral center. X-ray structures of the host and polymer have been reported here. Crystallographic characterization offers a detailed perspective on the structural and geometrical transformations in the polymer, enabling a systematic understanding of its optical properties. DFT and TD-DFT calculations strongly corroborate with the experimental findings.

Keywords: Chirality induction; Chirogenic process; Molecular design; Porphyrin trimer; Structural elucidation.