Unsymmetric Benzimidazole‐Fused Naphthalene Imides as Redox‐Active Chromophores With Broad Spectral Absorption
Guan‐Ru Lin, Huai‐Chih Chang, Yi‐Chen Wu, Chen‐Kai Hsieh, Chih‐Jou Chien, Guan‐Lin Lu, Makeshmuralikrishna Kulasekaran, Milanmathew Sssuraj, Tzu‐Ling Ho, Jatin Rawat, Hsien‐Hsin ChouABSTRACT
We report a concise synthesis of unsymmetric benzimidazole‐fused naphthalene imide (BfNI) and anhydride (BfNA) derivatives that addresses the long‐standing challenge of achieving broad absorption extending to ~750 nm within a structurally simple rylene framework. The unsymmetric π‐fusion strategy, combined with triarylamine donor incorporation via Pd‐catalyzed Suzuki–Miyaura cross‐coupling, bypasses conventional multistep protection–deprotection protocols and affords π‐extended chromophores with good processability. The resulting compounds exhibit dual‐band absorption spanning visible to near‐infrared with a narrowed optical bandgap of 1.60–1.65 eV, alongside stable reversible redox behavior confirmed by cyclic voltammetry. Time‐dependent DFT calculations further reveal pronounced charge‐transfer character with CT distances exceeding 9 Å, significantly larger than that of a symmetric reference. This molecular platform combining broad absorption, redox stability, and synthetic accessibility offers a promising design strategy for indoor light‐harvesting applications.