Near‐Infrared‐Emitting Helically Twisted Conjugated Frameworks Consisting of Alternant Donor‐π‐Acceptor Units and Multiple Boron Atoms

Abstract

AbstractA novel design strategy to construct bright and narrow near‐infrared (NIR) emission materials with suppressed shoulder peaks can significantly enhance their performance in various applications. Herein, we have successfully synthesized a series of helically twisted D‐π‐A conjugated systems bridged by boron atoms, achieving bright red to near‐infrared (NIR) emissions with notably narrow full‐width at half‐maximum (FWHM) values of 35 nm (0.08 eV) and photoluminescence quantum yields (PLQY) up to 80 %. These compounds display red‐shifted emissions up to 753 nm in higher concentrations. Cis/trans configurational isomers of multi‐boron‐bridged molecule BN3 exhibit similar photophysical properties. The unique combination of boron‐induced coordination‐enhanced charge transfer (CE‐CT) and the helically twisted conjugated framework is pivotal in achieving the red‐shifted, narrowband emission. X‐ray crystallographic analysis of BN2 and BN3‐a reveals that the extension of boron‐bridged D‐π‐A skeletons significantly increases the distortion of the skeleton. Systematic theoretical calculations show how the boron CE‐CT mechanism, in conjunction with the helical twist, leads to the narrowing of emission bands while simultaneously red‐shifting them into the NIR region. This work could open new avenues for the development of advanced materials with tailored optical properties, particularly in the challenging and highly sought‐after NIR spectrum.