4-Pyridyl-9,9′-spirobifluorenes as Host Materials for Green and Sky-Blue Phosphorescent OLEDs

Abstract

We report herein new pyridine-substituted spirobifluorene (SBF) dyes, i.e., 4-(9,9′-spirobi[fluoren]-4-yl)pyridine (4-4Py-SBF), 3-(9,9′-spirobi[fluoren]-4-yl)pyridine (4-3Py-SBF), and 2-(9,9′-spirobi[fluoren]-4-yl)pyridine (4-2Py-SBF), built on the association of the 4-substituted spirobifluorenyl core and various regioisomers of pyridine. These organic semiconductors possess high triplet energy levels (E T around 2.7 eV) in accordance with their use as hosts for green and sky-blue phosphorescent organic light-emitting diodes (PhOLEDs). These dyes have been synthesized from the 4-bromo-spirobifluorene (4-Br-SBF) platform, obtained from a new and efficient synthetic approach using the promising building block 4-bromofluorenone as a key intermediate. Synthesis, structural, thermal, electrochemical, and photophysical properties of the three dyes have been investigated in detail and compared to other model compounds, namely, 4-phenyl-SBF (4-Ph-SBF), 2-phenyl-SBF (2-Ph-SBF), and 2,4-pyridyl-SBF (2-4Py-SBF), in order to precisely study the influence of (i) the pyridine unit, (ii) the position of the nitrogen atom within the pyridyl core (in position 4, 3, or 2), and (iii) the substitution at the C4 position of SBF. This rational structure–properties relationship study sheds light on the effect of the substitution in position 4 of the SBF core and may pave the way to the development of such materials in electronics. Finally, the high performance of green PhOLEDs, ca. 63 cd/A, and of sky-blue PhOLED, ca.16 cd/A, clearly evidence the potential of these new SBF derivatives as hosts for phosphorescent dopants.

Spirobifluorene Regioisomerism: A Structure–Property Relationship Study

“…We note that compound c1 reported herein widens the scope of substituted fluorenone isomers as key building blocks for the synthesis of spiro derivatives for organics electronics. [14,[25][26][27] Pd Catalysed cross-coupling (Pd(dba) 2 , PCy 3 , KF, DMF, 130°C) between c1 and phenylboronic acid then gives the 1-phenylfluorenone d1 with a high yield of 85%. Thus, despite a sterically hindered environment, incorporation of pendant substituents in position 1 through Pd Catalysed cross-coupling is an interesting strategy to obtain 1-substituted fluorenone derivatives.…”

“…Indeed, in order to obtain a high triplet energy (E T ), key feature in the design of host materials for blue PhOLEDs, which are still the weakest link of this technology, it is mandatory to restrict the π-electrons delocalization within the OSC. This π-conjugation disruption has been successfully investigated with ortho linked SBFs (substitution in position 4) [12][13][14][15][16] and meta linked SBFs (substitution in position 3), [2,[17][18][19][20] leading to high performance blue PhOLEDs. However and despite the recent very high efficiency devices obtained by Jiang et al, [17] and by our groups [15] only few examples of 3-and 4-substituted SBFs have been described to date and more importantly no rational structure-properties relationship studies have been reported on SBF regioisomerism.…”

Electron-Rich 4-Substituted Spirobifluorenes: Toward a New Family of High Triplet Energy Host Materials for High-Efficiency Green and Sky Blue Phosphorescent OLEDs

“…[32][33][34][35] As it is known that the increase of HOMO energy levels through the incorporation of phenylacridine, [36][37][38][39] indoloacridine, [40][41][42] quinolinophenothiazine 43 or quinolinophenoxazine 44 moieties instead of a fluorene core has remarkable consequences on the device performance we wish to report herein the first examples of 4-substituted SBF derivatives incorporating electronrich fragments, namely N-phenylcarbazole in 4-PhCz-SBF and trimethoxyphenyl in 4-Ph(OMe) 3 -SBF, Scheme 1. Through a detailed structure-properties relationship study with the corresponding building blocks, namely 4-phenyl-spirobifluorene (4-Ph-SBF), spirobifluorene (SBF), 1,2,3-trimethoxybenzene (Ph(OMe) 3 ) and N-phenyl-carbazole (N-PhCz), we highlight herein the remarkable influence of the C4-substituent on the electronic properties.…”

“…34,35 Thus, and despite the π-conjugation disruption between the fluorene and its substituent in C4, it has been shown in these previous works that electron-withdrawing groups such as pyridine isomers or pyrimidine (Chart 1) can selectively decrease the LUMO energy levels (localized on the electron poor moiety and/or on the adjacent fluorene core) keeping nevertheless the HOMO energy level (localized on the SBF core) unaltered. 32,33 However, the opposite strategy, that is increasing the HOMO energy level of 4-substituted SBFs, has to the best of our knowledge never been explored.…”

Synthesis and Electroluminescence Properties of 3-(Trifluoromethyl)phenyl-Substituted 9,10-Diarylanthracene Derivatives for Blue Organic Light-Emitting Diodes

“…Extremely pure red, green, and blue luminophores with high electrochemical stability and efficiency are particularly essential for a vivid full-color display in organic light-emitting diodes (OLEDs). To date, OLED materials for red and green emission with high performance have been developed [3][4][5][6][7][8][9][10][11]. However, continuous efforts to enhance stability and efficiency in blue fluorescent materials, which possess relatively low chemical and electrochemical properties, caused by the intrinsic wide band-gap, are still required [12,13].…”