Naphthalimide-Fused Subphthalocyanines: Electron-Deficient Materials Prepared by Cascade Annulation

Imide-fused porphyrinoids are becoming key components in the area of molecular materials. Herein we report the synthesis of naphthalimide (NMI)-annulated subphthalocyanines (SubPcs) designed as an NIR-absorbing n-type organic semiconductor. Two different synthetic pathways could be applied for the preparation of NMI-fused SubPcs. The first consists of a [3 + 2] annulation between SubPc boronic ester and dibromo-NMI. This annulation, which involves the first CH activation reaction of a SubPc derivative reported so far, is totally regioselective to the β-position. Density functional theory (DFT) indicated that such position is favored both kinetically and thermodynamically. On the other hand, the second method relies on a cyclotrimerization of NMI-fused phthalonitrile. Electrochemical measurements and DFT calculations revealed that these NMI-fused SubPcs have low-lying LUMO energy levels suitable for electron charge transport. The N-alkyl substituted derivative (NMI-SubPc 2) was successfully applied as an nonfullerene acceptor (NFA) in combination with donor polymer PM6 in bulk-heterojunction (BHJ) organic solar cells (OSCs) with a highest power conversion efficiency (PCE) of 7.0%. This value is comparable to the record PCE of SubPc derivatives in BHJ-OSCs. Our results open a new vista in the preparation of π-extended contracted porphyrinoids and substantiate the potential of this new class of strong-absorbing electron-acceptor materials for applications in optoelectronic devices.