From Yellow to Red: Emission Tuning of Benzothioxanthene Imides Through Selective Multi-Arylamine Functionalization

The selective bis- and tris-functionalization of benzothioxanthene imides (BTI) with extended triphenylamine (eTPA) units, enabling precise tuning of optical and electronic properties, is introduced herein. Controlled bromination and subsequent Suzuki-Miyaura cross-coupling allow modular introduction of donor groups, resulting in redshifted emission into the red-near-infrared (NIR) region with large Stokes shifts and fluorescence quantum yield strongly modulated by solvent polarity and molecular environment. Photoemission measurements reveal HOMO stabilization upon addition of the third eTPA, illustrating the impact of subtle structural modifications on frontier orbital energies in the solid state. Both derivatives exhibit excellent film-forming and solvent-resistance properties, enabling, as an early proof of concept, their incorporation as emissive guests in solution-processed flexible organic light-emitting devices (OLEDs). Remarkably, while spectral variations were small, the third eTPA unit induces pronounced differences in device performance, illustrating how minimal and simple molecular modifications can deliver substantial functional gains.