Rylene Ribbons with Unusual Diradical Character

Armchair graphene nanoribbons (AGNRs) with a width of N = 3p + 2 are theoretically predicted to be metallic or half-metallic with a very small bandgap. The narrowest AGNR of this type is polyrylene (5-AGNR, N = 5), which has never been successfully synthesized by wet chemistry. In this work, we successfully synthesized a series of soluble and stable long rylene molecules up to dodecarylene by using a newly developed cyclopenta (CP) ring-fused perylene building block. Importantly, we found that from hexarylene onward, they showed very unusual open-shell singlet diradical character with a small singlet-triplet gap, which is closely related to the theoretically predicted metallic or half-metallic property of the infinite rylene ribbon. Their energy gaps (E-g) showed clear chain-length dependence, and a linear extrapolation of the E-g similar to 1/n plot predicted that the infinite 5-AGNR fused by CP rings has a small bandgap of 0.21 eV.