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.
Bibliographical noteFunding Information:
The work was supported by JSPS KAKENHI Grants Numbers 25220802, 25620031, and 15K05663. K.N. and D.S. acknowledge JSPS Fellowship for Young Scientists. The research at Yonsei University was supported by the Global Research Laboratory (GRL) Program (2013K1A1A2A02050183) of the Ministry of Education, Science and Technology (MEST) of Korea.
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All Science Journal Classification (ASJC) codes
- Organic Chemistry