BAr2‐Bridged Azafulvene Dimers with Tunable Energy Levels for Photostable Near‐Infrared Dyes

Abstract

AbstractOrganic dyes with strong absorption in the near‐infrared (NIR) region are potentially useful in medical applications, such as tumor imaging and photothermal therapy. In this work, new NIR dyes combining BAr2‐bridged azafulvene dimer acceptors with diarylaminothienyl donors in a donor–acceptor–donor configuration were synthesized. Surprisingly, it was found that in these molecules the BAr2‐bridged azafulvene acceptor adopts a 5‐membered, rather than 6‐membered ring structure. The influence of the aryl substituents on the HOMO and LUMO energy levels of the dye compounds was assessed from electrochemical and optical measurements. Strong electron‐withdrawing fluorinated substituents (Ar=C6F5, 3,5‐(CF3)2C6H3) lowered the HOMO energy while preserving the small HOMO–LUMO energy gap, resulting in promising NIR dye molecules that combine strong absorption bands centered around 900 nm with good photostability.