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From Open‐Shell Singlet Diradicaloid to Closed‐Shell Global Antiaromatic Macrocycles
Author(s) -
Li Guangwu,
Gopalakrishna Tullimilli Y.,
Phan Hoa,
Herng Tun Seng,
Ding Jun,
Wu Jishan
Publication year - 2018
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201803949
Subject(s) - antiaromaticity , diradical , open shell , singlet state , chemistry , intramolecular force , trimer , antiferromagnetism , tetramer , photochemistry , molecule , stereochemistry , dimer , aromaticity , organic chemistry , physics , enzyme , excited state , condensed matter physics , nuclear physics
A dithieno[a,h]‐s‐indacene‐ (DTI‐) based diradicaloid DTI‐2Br was synthesized and its open‐shell singlet diradical character was validated by magnetic measurements. On the other hand, its macrocyclic trimer DTI‐MC3 and tetramer DTI‐MC4 turned out to be closed‐shell compounds with global antiaromaticity, which was supported by X‐ray crystallographic analysis and NMR spectroscopy, assisted by ACID and 2D‐ICSS calculations. Such change can be explained by a subtle balance between two types of antiferromagnetic spin–spin coupling along the π‐conjugated macrocycles. The dications of DTI‐MC3 and DTI‐MC4 turned out to be open‐shell singlet diradical dications, with a singlet–triplet energy gap of −2.90 and −2.60 kcal mol −1 , respectively. At the same time, they are both global aromatic. Our studies show that intramolecular spin–spin interactions play important roles on electronic properties of π‐conjugated macrocycles.