5 years ago

Thienylquinonoidal Porphyrins and Hexaphyrins with Singlet Diradical Ground States

Thienylquinonoidal Porphyrins and Hexaphyrins with Singlet Diradical Ground States
Atsuhiro Osuka, Daiki Shimizu, Dongho Kim, Ko Furukawa, Jun Oh Kim, Koji Naoda
To explore stable organic diradicaloids, meso-thienylquinonoid-substituted porphyrins Pn and hexaphyrins Hn, where “n” denotes the number of thienyl units in the meso-substituents, were synthesized. P0 was identified as a closed-shell quinonoid, whereas P1 was shown to possess significant diradical character with diradical character index (y) of 0.99 and quite small singlet-triplet energy gap (ΔES-T) of −0.13 kcal mol−1. P1 was certainly stable, allowing its isolation, but decomposed gradually in solution. In the hexaphyrin series, it was shown that H0 and H1 were closed-shell quinonoids, but H2 was a highly stable diradicaloid with y=0.85 and ΔES-T of −3.72 kcal mol−1. The high stability of H2 was ascribed to effective spin delocalization over the entire conjugated network. Characteristically, H2 displays an intense absorption band in NIR region at λmax=1175 nm with molar absorption coefficient (ϵ) of 8.81×104 mol−1 L cm−1, a narrow HOMO–LUMO gap of 0.69 eV, and nine reversible redox potential waves. Radical state: Oligothienylquinonoid-substituted porphyrins Pn and hexaphyrins Hn (n=0–2) were synthesized. P0 has been shown to be a closed-shell quinonoid, whereas P1 has been shown to be a diradical that is sensitive toward air and moisture. H0 and H1 have been shown to be quinonoids, whereas H2 has been characterized as a remarkably stable diradical with singlet ground state owing to the effective spin delocalization over the whole conjugated circuit.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701355

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