Postsynthetic Annulative π‐Extension of Subphthalocyanines: Triphenylene‐ and [5]Helicene‐Fused Chromophores

Postsynthetic annulative π‐extension offers a direct route to reshape the π‐surface of subphthalocyanines (SubPcs) without exposing elaborate phthalonitrile precursors to the harsh cyclotrimerization conditions. Here, a β,β ‐diiodo SubPc undergoes twofold Suzuki–Miyaura cross‐coupling with biphenyl‐2,2′‐diboronic acid or racemic [1,1′‐binaphthalene]‐2,2′‐diboronic acid to afford triphenylene‐fused 1 and [5]helicene‐fused 2 in 40% and 43% yield, respectively. Annulation redshifts the Q‐band absorption and fluorescence maxima by up to 30 and 34 nm and increases the fluorescence quantum yield in CHCl 3 from 0.25 for parent SubPc 0 to 0.36 and 0.45 for 1 and 2 . Electrochemistry and density functional theory indicate only modest changes in the frontier‐orbital energies, with the low‐energy electronic structure remaining largely SubPc‐centered. Localized concentration‐ and temperature‐dependent 1 H NMR shifts are consistent with lateral association involving the annulated polycyclic aromatic surface. Compound 2 is configurationally labile, but its enantiomers can be resolved by chiral HPLC and display mirror‐image circular dichroism across the visible region before racemizing over several hours in dilute solution.