Exact benzannulation regulates packing and circularly polarized luminescence in a chiral bilayer nanographene

Abstract

Exact π-extension offers a molecularly precise approach for interrogating how peripheral structural modification governs the conformation, packing, and chiroptical response of atomically defined chiral nanographenes. Here we report DN-1, a naphthalene-extended chiral bilayer nanographene that reveals the regulatory role of peripheral benzannulation in supramolecular organization and circularly polarized luminescence. DN-1 was obtained by Scholl cyclodehydrogenation, forming 27 C–C bonds in a single operation. Single-crystal X-ray diffraction established a C2 symmetric bilayer architecture bearing peripheral naphthalene units and a short intramolecular interlayer separation of 2.945 Å. Notably, benzannulation does more than expand the π-surface: it reorganizes the solid-state packing and enables extensive intermolecular π-overlap involving up to 32 benzene rings. NMR spectroscopy and HRMS analyses verified the molecular identity, while NICS, AICD, and TD-DFT calculations clarified the aromaticity distribution and excited-state electronic structure. After chiral resolution, DN-1 displayed broad visible absorption, red emission at 677 nm, mirror-image circular dichroism, and circularly polarized luminescence at ca. 682 nm with |glum| values up to 1.79 × 10−2. These results establish exact benzannulation as a molecular design principle for linking peripheral π-extension, supramolecular packing, and CPL activity in chiral nanographenes.