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 CHCl3 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 1H 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.