A Dimeric π‐Stacking of Anthracene Inducing Efficiency Enhancement in Solid‐State Fluorescence and Non‐Doped Deep‐Blue Triplet–Triplet Annihilation Organic Light‐Emitting Diodes

Abstract

Triplet–triplet annihilation (TTA) mechanism utilizing the conversion of low triplet energy excitons to generate singlet excitons has been successfully employed in realizing highly efficient fluorescent organic light‐emitting diodes (OLEDs). Herein, new anthracene‐based TTA molecules (TPNACN and TPBACN) are developed as deep‐blue emitters for high‐efficiency non‐doped TTA‐OLEDs. Their structural, physical, and photophysical properties are experimentally and theoretically investigated. These compounds in solid‐state exhibit different photophysical properties due to a discrepancy in the molecular packing. Particularly, in the crystal of TPNACN, anthracene moieties are arranged with dimeric π–π stacking, and the material shows a strong excimer emission in the deep‐blue region with ΦPL close to the ideal theoretical value. The non‐doped TTA‐OLED based on TPNACN attains a high maximum external quantum efficiency of 7.89% (6.63 cd A−1) with a low turn‐on voltage of 2.6 V, and displays deep‐blue emission with CIE coordinates of (0.146, 0.101). These results prove that a separated dimeric π‐stacked molecular alignment of anthracene enhances not only the fluorescence efficiency in the solid state but also the ratio of singlet exciton harvested by the TTA process in the device, bringing about excellent device electroluminescent properties. This can be a new tactic to designing new emissive materials for efficient OLED devices.

Challenges, progress and prospects in solid state triplet fusion upconversion

“…Blue OLEDs, which are desired in organic displays, have been demonstrated to exhibit TTA: triplet-triplet-upconversion OLEDs (TTU-OLEDs). [142][143][144] In this way, the maximum quantum yield is increased from 25% to 62.5% (25 + 0.5 Â 75). Recently Han et al demonstrated TTU-OLEDs using substituted anthracene derivatives with high solid-state quantum yield.…”

“…In the case of anthracene derivatives, it is achieved through bulky substituents and exergonic TTA. [142][143][144] Without a TTA driving force (e.g. rubrene), efficient upconversion requires a delicate balance of rate constants and remains a challenging proposition.…”

Nearly 100% Exciton Utilization via Hybridized Inter‐ and Intramolecular Triplet Exciton Harvesting Channels in Blue Fluorescent Organic Light‐Emitting Diodes

“…The efficiency of blue fluorescent devices can be enhanced by three mechanisms, namely, thermally activated delayed fluorescence (TADF), [10,15] hybrid local and charge transfer (HLCT), [16][17][18][19] and triplet-triplet fusion (TTF). [20][21][22][23][24][25][26][27] All three mechanisms involve the conversion of nonemissive triplet excitons to singlet excitons. Among the three pathways, the TTF-based blue devices have shown good operational lifetime along with excellent resistance to the efficiency roll-off at high luminance and thus, emerged as potential candidates for practical applications.…”

Deep-blue high-efficiency triplet–triplet annihilation organic light-emitting diodes using hydroxyl-substituted tetraphenylimidazole-functionalized anthracene fluorescent emitters

“…11 Recently, deep-blue triplet–triplet annihilation (TTA) materials were considered as they can accomplish 62.5% of the IQE, utilizing molecular interaction and the fusion of two individual first triplet excited excitons to produce the first singlet excited excitons. 12 Until now, most efficient TTA emitters are based on anthracene, such as 4-cyanophenyl anthracene derivatives, 3 e ,13 in which anthracene with a large flat conjugated structure favors bimolecular interactions and can stabilize the triplet pair while the 4-cyanophenyl part facilitates the TTA process by improving the molecular interactions. 3 e ,13 a Moreover, there was an available position left on the anthracene unit of the 4-cyanophenyl anthracene, which has been functionalized by various moieties to tune the optical properties of the molecules.…”

“…12 Until now, most efficient TTA emitters are based on anthracene, such as 4-cyanophenyl anthracene derivatives, 3 e ,13 in which anthracene with a large flat conjugated structure favors bimolecular interactions and can stabilize the triplet pair while the 4-cyanophenyl part facilitates the TTA process by improving the molecular interactions. 3 e ,13 a Moreover, there was an available position left on the anthracene unit of the 4-cyanophenyl anthracene, which has been functionalized by various moieties to tune the optical properties of the molecules. 13,14 Since TTA molecules based on 4-cyanophenyl anthracene fragment have been fully investigated, in this work, we would like to propose a new approach for designing anthracene-based deep-blue TTA emitters.…”