Unlocking room temperature phosphorescence in dibenzothiophene-based systems via the Scholl reaction

Abstract

A family of butterfly-shaped diphenanthro[9,10-b:9′,10′-d]thiophene derivatives has been straightforwardly synthesized from tetrabromothiophene via consecutive Suzuki-Miyaura and Scholl reactions, targeting potential charge-transporting and light-emitting organic materials. Indeed, time of flight measurements displayed hole mobility values up to 4.7 × 10⁻⁵ cm² V⁻¹ s⁻¹ under an applied electric field of 6 × 10⁵ V cm⁻¹. Spectroscopic studies showed promising photoluminescence, with quantum yields up to 27.5 % and adjustable emissions ranging from deep blue to sky blue in solution and in solid films, respectively. Moreover, the synthesized compounds revealed room-temperature phosphorescence when introduced as dopants in Zeonex films, a highly sought-after characteristic in metal- and halogen-free organic materials. This phenomenon delineates a spectral transition from deep blue to warm-white emission as the environment shifts from air-equilibrated to vacuum conditions, which entails different applications such as lighting or oxygen-sensing devices. Phosphorescence, which was further corroborated in dilute solutions of THF at 77 K, does not occur on the non-cyclized synthetic precursors, demonstrating the key role of the Scholl reaction to unlock it. These findings make evidence of the potential of this core for advancing optoelectronic device functionalities.