Counteranion-Controlled Iodocyclizations Enabled by Iodine Nitrate: A Modular Route to Functionalized Triphenylenes and All-Benzenoid Graphene Quantum Dots

Symmetrically functionalized triphenylenes are desirable building blocks for modular nanographene construction, yet general methods for the direct synthesis of C3-symmetric triiodofunctionalized triphenylenes (SITEs) remain elusive. Here we report a robust four-step route to SITEs via a Grignard-Sonogashira-iodocyclization-aromatization (GSIA) sequence of simple, scalable transformations. The key step is a triple 6-endo-dig cyclization of 1,3,5-tris-arylalkynylbenzenes enabled by iodine nitrate (INO3), introduced here as a powerful iodocyclization reagent. Unlike conventional I-X reagents such as ICl, INO3 avoids competing halogenation, delivering clean triiodinated products across electron-rich and electron-deficient substrates, while the bis(pyridine)iodonium reagent IPy2BF4 fails to cyclize these substrates even under acid-activated conditions. The resulting SITEs are symmetry-matched hubs for π-extension into a homologous series of all-benzenoid graphene quantum dots, the π-extended triphenylenes (PETs), containing 36, 54, 72, 90, and 126 graphenic carbons. This series shows three properties that run counter to expectations for polycyclic aromatics. First, nonradiative decay of S1 slows as the PETs grow and red-shift, violating the energy gap law, and is suppressed by nearly 3 orders of magnitude relative to an acene of comparable gap. Second, fluorescence quantum yield peaks at the largest, most red-shifted member (C126, 8.2%). Third, C126 is harder to oxidize than the smaller C90 (E1/2 = 0.27 V versus 0.034 V) despite 36 additional π-electrons, pointing to shape and supramolecular contributions that override simple π-electron counting. Together, this work establishes INO3 as a general solution to counteranion-driven side-reactivity in iodocyclizations and delivers a modular platform for the assembly of Clar-type nanographenes.