Synthesis, photoluminescence, and electroluminescence characterization of double tetraphenylethene-tethered BODIPY luminogens

Abstract

Three double tetraphenylethene (TPE)-tethered 4-difluoro-4-bora-3a,4a-diaza-s-indance (BODIPY) fluorophores, 35TPEBODP, 88TPEBODP, and 26TPEBODP, have been synthesized and characterized. The green 35TPEBODP with deep red fluorescence shows serious thermal decomposition in the purification process of sublimation, which prohibits its test for an organic light-emitting diode (OLED) fabricated by the vacuum-thermal evaporation process. The tethered TPE is attached to BODIPY at three different positions, resulting in different photoluminescence (emission wavelength and quantum yield) and electroluminescence (EL). Different from TPE-tethered BODIPY fluorophores reported in literature, none of the BODIPY fluorophores studied here exhibits aggregation-induced emission (AIE), aggregation-induced enhanced emission (AIEE), or twisted intramolecular charge transfer (TICT) characteristics. Although solution (10(-5) M THF) photoluminescence quantum yields (phi s) are relatively high at 78%, 68%, and 86% for 35TPEBODP, 88TPEBODP, and 26TPEBODP, respectively, which are all higher than 41% of PhBODP (a non-TPE-tethered BODIPY), the phi is significantly decreased to 1-6% in 5 wt% dopant polystyrene thin film or as a solid powder, except for 13% of 26TPEBODP. Therefore, due to the low phi of dopant thin film or solid powder, either dopant or nondopant OLEDs exhibit inferior external quantum efficiency (EQE) and intensity of EL. The best OLED in this study is the 26TPEBODP device, and its EQE reaches 1.3%, and the highest EL intensity is approximately 1,600 cd/m(2).