Efficiency of Thermally Activated Delayed Fluorescence Sensitized Triplet Upconversion Doubled in Three‐Component System

Abstract

As in many fields, the most exciting endeavors in photon upconversion research focus on increasing the efficiency (upconversion quantum yield) and performance (anti‐Stokes shift) while diminishing the cost of production. In this vein, studies employing metal‐free thermally activated delayed fluorescence (TADF) sensitizers have garnered increased interest. Here, for the first time, the strategy of ternary photon upconversion is utilized with the TADF sensitizer 2,4,5,6‐tetrakis(carbazol‐9‐yl)isophthalonitrile (4CzIPN), resulting in a doubling of the upconversion quantum yield in comparison to the binary system employing p‐terphenyl as the emitter. In this ternary blend, the sensitizer 4CzIPN is paired with an intermediate acceptor, 1‐methylnaphthalene, in addition to the emitter molecule, p‐terphenyl, yielding a normalized upconversion quantum yield of 7.6% while maintaining the 0.83 eV anti‐Stokes shift. These results illustrate the potential benefits of utilizing this strategy of energy‐funneling, previously used only with heavy‐metal based sensitizers, to increase the performance of these photon upconversion systems.

Approaching the Spin-Statistical Limit in Visible-to-Ultraviolet Photon Upconversion

“… 28 − 30 The remaining systems yielded Φ UC,g values ranging from 4 to 14%, and full results are presented in Figure 2 C and Table 3 . It should be noted that the values achieved for TP (12.6%) and PPD (5.8%), which both emit from singlet states just shy of 4 eV, are multifold improvements on that previously reported 30 , 63 and likely result from more efficient TET and, subsequently, more efficient TTA between triplets. The external Φ UC measured for our specific setup yielded Φ out between 0.7 and 0.85, resulting from significant reabsorption of the samples.…”

Triplet–triplet annihilation upconversion combined with afterglow phosphors for multi-dimensional anti-counterfeiting and encoding

“…Besides, the invisible high power NIR laser may cause potential damage to human eyes during daily use. Among other UC mechanisms, triplet-triplet annihilation upconversion (TTA-UC) (also known as low-power upconversion 37 ), formed by the sensitizer/annihilator dye pair, 38,39 has the advantages of high UC efficiency, variable excitation and emission positions, and low excitation power threshold, [40][41][42] which make it a promising alternative for UCinvolved applications, especially for solar energy 43 and ratiometric sensing. 44,45 Recently, utilizing the TTA-UC emission as the excitation source or energy transfer donor has attracted great research interest.…”

Multifaceted Sulfone–Carbazole-Based D–A–D Materials: A Blue Fluorescent Emitter as a Host for Phosphorescent OLEDs and Triplet–Triplet Annihilation Up-Conversion Electroluminescence

“…However, the EQE values of conventional fluorescent emitters are limited to ∼5%. Many studies have focused on developing highly efficient fluorescent emitters with a maximum IQE (≥25%) using the non-radiative triplet (T 1 ) up-conversion mechanism, such as triplet–triplet annihilation up-conversion (TTAUC). − Hybridized local and charge-transfer excited state has been exploited to achieve a breakthrough in blue fluorescent OLEDs. , Thus, there is a strong demand for robust, high-performing, and cost-effective deep-blue and blue OLEDs.…”

“…Under the triplet up-conversion mechanism, the IQE of a fluorescent molecule can exceed 25%; for example, IQE values of ∼65 and 100% have been realized through triplet–triplet annihilation (TTA) and hybridized local and charge-transfer states, respectively. Consequently, a fluorescent molecule involving these up-conversion mechanisms is deemed to be a promising candidate for developing efficient blue fluorescent emitters . TTA becomes the primary up-conversion mechanism of the triplet state without causing an increase in the radiative lifetime owing to the better understating triplet energy transfer mechanism and molecular design .…”