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Abstract In this manuscript, we report the first demonstration of controlled helicity in extended graphene nanoribbons (GNRs). We present a wealth of new graphene nanoribbons that are a direct consequence of the high‐yielding and robust synthetic method revealed in this study. We created a series of defect‐free, ultralong, chiral cove‐edged graphene nanoribbons where helical twisting of the graphene nanoribbon backbone is tuned through functionalization with chiral side chains.S‐configured point chiral centers in the side chains transfer their chiral information to induce a helically chiral, right‐handed twist in the graphene nanoribbon. As the backbone is extended, these helically twisted graphene nanoribbons exhibit a substantial increase in their circular dichroic response. The longest variant synthesized consists of an average of 268 linearly fused rings, reaching 65 nm in average length with nearly 10 full end‐to‐end helical rotations. The structure exhibits an extraordinary |Δε| value of 6780 M⁻¹cm⁻¹at 550 nm—the highest recorded for an organic molecule in the visible wavelength range. This new chiroptic material acts as room‐temperature spin filters in thin films due to its chirality‐induced spin selectivity. 

Abstract Addition of the bipyridyl‐embedded cycloparaphenylene nanohoop bipy[9]CPP to [Fe{H₂B(pyz)₂}] (pyz=pyrazolyl) produces the distorted octahedral complex [Fe(bipy[9]CPP){H₂B(pyz)₂}₂] (1). The molecular structure of1shows that the nanohoop ligand contains a non‐planar bipy unit. Magnetic susceptibility measurements indicate spin‐crossover (SCO) behaviour with aT_1/2of 130 K, lower than that of 160 K observed with the related compound [Fe(bipy){H₂B(pyz)₂}₂] (2), which contains a conventional bipy ligand. A computational study of1and2reveals that the curvature of the nanohoop leads to the different SCO properties, suggesting that the SCO behaviour of iron(II) can be tuned by varying the size and diameter of the nanohoop.