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Propeller‐Shaped Semi‐fused Porphyrin Trimers: Molecular‐Symmetry‐Dependent Chiroptical Response
Author(s) -
Kato Kenichi,
Osuka Atsuhiro
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202002157
Subject(s) - porphyrin , propeller , symmetry (geometry) , materials science , crystallography , chemistry , photochemistry , engineering , geometry , mathematics , marine engineering
Triple helicene‐like semi‐fused trimeric Ni II porphyrins were constructed by alkyne trimerization of an ethynyl‐substituted porphyrin and subsequent three‐fold Grignard addition to the formyl groups and acid‐catalyzed intramolecular cyclization. The presence of stereogenic sp 3 carbons in the central bridge leads to small inter‐porphyrin conjugative interactions as was revealed by electrochemical and optical properties. Two diastereomers with stable chiral conformations were optically resolved, and the separated enantiomers displayed considerably intense circular dichroism. Importantly, the chiroptical response of C 3 ‐symmetric helical isomer (|Δ ϵ |=830 m −1 cm −1 ) is 1.8 times amplified from that of C 1 ‐symmetric one (|Δ ϵ |=470 m −1 cm −1 ). The observed amplification has been interpreted in terms of different spatial arrangements of the three porphyrins.