A cyclopenta-fused dibenzo[b,d]thiophene-co-phenanthrene macrocyclic tetraradicaloid

A cyclopenta-fused macrocyclic tetraradicaloid, MC4-S, containing alternating phenanthrene (Phen) and dibenzo[b,d]thiophene (DBTh) units was synthesized and isolated in single-crystal form. Compared with its all-carbon isoelectronic structure, CPTP-M, the incorporation of two sulfur atoms leads to a smaller radical character and a larger singlet-triplet energy gap. X-ray crystallographic analysis reveals that the spin-spin coupling through the DBTh unit is stronger than that through the Phen moiety. In addition, the electron-rich sulfur atoms also raise the energies of both the HOMO and LUMO in MC4-S, but the overall optical and electronic energy gaps are close to that of the CPTP-M. MC4-S displays global anti-aromaticity according to the NMR measurements and theoretical calculations (NICS, ACID and 2D ICSS), with a 36 pi ring current circuit along the all-carbon periphery excluding the two sulphur atoms. Its dication becomes globally aromatic due to the existence of a dominant 34 pi-conjugation pathway. This study sheds some light on the effect of heteroatoms on the electronic properties of open-shell polyradicaloids.

Automated summary

A novel cyclopenta-fused macrocyclic tetraradicaloid, MC4-S, containing alternating phenanthrene and dibenzo[b,d]thiophene units, was synthesized and characterized. The two sulfur atoms in MC4-S lead to a smaller radical character and a larger singlet-triplet energy gap compared to its all-carbon isoelectronic structure, CPTP-M. X-ray crystallographic analysis revealed stronger spin-spin coupling through the DBTh unit than through the Phen moiety. The presence of electron-rich sulfur atoms raised the energies of both the HOMO and LUMO in MC4-S, while overall optical and electronic energy gaps remained similar to CPTP-M.