Design Strategy of Anthracene-Based Fluorophores toward High-Efficiency Deep Blue Organic Light-Emitting Diodes Utilizing Triplet–Triplet Fusion

Abstract

In contrast to the red and green regions, conventional fluorescent emitters continue to serve as blue emitters in commercialized organic light-emitting diodes. Many researchers have studied anthracene moieties as blue emitters, given their appropriate energy levels and good emission properties. We herein report two new deep blue-emitting anthracene derivatives that include p-xylene as moieties connecting the anthracene cores to side groups. We enhanced the efficiency by maximizing triplet− triplet fusion (TTF) without sacrificing emission color. The large steric hindrance imposed by the methyl groups of p-xylene creates a perpendicular geometry between p-xylene and the neighboring aromatic rings. Any extension of π-conjugation is thus disrupted, and the isolated core anthracene moiety emits a deep blue color with a high photoluminescence quantum yield. Moreover, the extensive steric hindrance suppresses vibration and rotation because the molecules are rigid. The high horizontal dipole ratio attributable to the large aspect ratio increases the outcoupling efficiency of the emitted light. Furthermore, the charge mobility and triplet harvesting ability are enhanced by decreasing the bulkiness of the side groups. Molecular dynamics simulation revealed that the bulkiness of the side group significantly impacted molecular density, which in turn affected the charge transport and TTF. We used two molecules, 2PPIAn (containing a phenyl side group) and 4PPIAn (containing a terphenyl side group), to form nondoped emission layers that exhibited maximum external quantum efficiencies of 8.9 and 7.1% with Commission Internationale de L'Eclairage coordinates of (0.150, 0.060) and (0.152, 0.085), respectively.

Double Ring-Closing Approach for the Synthesis of 2,3,6,7-Substituted Anthracene Derivatives

“…21 The crude product was purified by crystallization from chloroform to afford white needles of compound 1 in a yield of 57% (9.91 g, 33.9 mmol). 1…”

“…Frame data were reduced to intensity values with SAINT-Plus 1 and a correction for absorption effects applied using the multi-scan approach implemented in SADABS. 1 The structures were solved with SHELXT 2 and refined against F 2 using Jana2006. 3 Non-H atoms were refined with anisotropic displacement parameters.…”

“…Anthracene derivatives have been widely studied as materials for organic electronics and other applications and continue to be of immense interest in various fields of materials chemistry and beyond. [1][2][3][4][5][6][7][8][9] New synthetic methods keep being developed to facilitate the preparation of known anthracene derivatives and to enable the preparation and study of new derivatives, e.g. our recently developed method for the synthesis of substituted 9,10-anthracenedicarbonitriles (also known as 9,10dicyanoanthracenes).…”

“…The reaction solution was then concentrated to approx. 15 mL and allowed to slowly cool to r.t. for crystallization of compound 2a.Filtration and washing with cold toluene and petroleum ether afforded 2a as white solid in a yield of 77% (1.76 g, 4.6 mmol) 1. H NMR (600 MHz, CDCl3): δ 7.77 (s, 2H), 6.03 (s, 2H), 4.17 -4.04 (m, 8H); 13 C NMR (150 MHz, CDCl3): δ 139.3, 132.3, 121.9, 101.9, 65.7; HRMS (m/z): [M+H] + calcd.…”

Double Ring-Closing Approach for the Synthesis of 2,3,6,7-Substituted Anthracene Derivatives

“…21 The crude product was purified by crystallization from chloroform to afford white needles of compound 1 in a yield of 57% (9.91 g, 33.9 mmol). 1 After stirring at r.t. for 2 h, the resulting yellow solution of Wittig reagent 4 was used directly for the synthesis of compound 5 (no work-up or purification).…”