Preparation of Near-Infrared Emissive π-Conjugated Polymer Films Based on Boron-Fused Azobenzene Complexes with Perpendicularly Protruded Aryl Substituents

Abstract

Most organic luminescent dyes usually show poor emission in solid due to aggregation-caused quenching due to nonspecific intermolecular interaction, such as π–π stacking. Furthermore, since commodity molecules having near-infrared (NIR) emission properties tend to have extended π-conjugated systems, development of luminescent organic materials with solid-state NIR emission has been still challenging. Herein, the series of the azobenzene complexes with the perpendicularly-protruded aryl derivative at the boron atom toward π-conjugated system is synthesized. From the optical measurements, it is shown that these complexes can show crystallization-induced emission enhancement behaviors. The donor–acceptor type π-conjugated polymers composed of the azobenzene complexes are also synthesized. Highly-efficient NIR emission from the phenyl-substituted polymers both in solution (λ[PL] = 742 nm, Φ[PL] = 15%) and film states (λ[PL] = 793 nm, Φ[PL] = 9%) is obtained. Furthermore, emission wavelengths can be tuned by changing the substituent at the boron atom to the modified aryl groups. From mechanistic studies including theoretical calculations, it is shown that electronic interaction is allowable between the aryl substituent to the π-conjugated system through the tetradentate boron.