1-Carbazolyl Spirobifluorene: Synthesis, Structural, Electrochemical, and Photophysical Properties

Abstract

The present work reports one of the rare examples of a new emerging family of spirobifluorene derivatives, namely 1-substituted spirobifluorenes. We report the synthesis and the structural, electrochemical and photophysical properties of 9-(9,9'-spirobi[fluorene]-1-yl)-9H-carbazole 1-Cbz-SBF, constructed from the connection of the widely known electron-rich carbazole fragment at the C1 position of spirobifluorene. We show with 1-Cbz-SBF that the substitution at C1 induces two important characteristics which drive the electronic properties. First, there is a complete conjugation breaking between the pending substituent, herein carbazole, and the substituted fluorene. Second, there is a through space interaction between the carbazole and its cofacial fluorene. Thanks to a structure-property relationship approach with its constituting building blocks 9,9'-spirobifluorene SBF and carbazole Cbz, we show how some electronic properties are driven by the carbazole unit such as the HOMO energy level whereas others are driven by the fluorene such as the triplet state energy level. As 1-substituted spirobifluorenyl represents a new and promising molecular scaffold for PhOLED applications and more generally for organic electronics, such study provides fundamental knowledge to design future organic materials for specific applications.

Molecular Engineering of Cyano‐Substituted Carbazole‐Based Host Materials for Simultaneous Achievement of High Efficiency and Long Lifetime in Blue Phosphorescent Organic Light‐Emitting Diodes

“…The 1CNCzBN exhibited large twisting between the cyanocarbazole and benzonitrile units with a large dihedral angle of 70.6° compared to small dihedral angles of 2CNCzBN (59.1°), 3CNCzBN (58.4°), and 4CNCzBN (57.4°). [ 49 ] The large dihedral angle of 1CNCzBN hinders effective conjugation between the cyanocarbazole and benzonitrile units and resulted in the blue‐shifted absorption. In the case of 2CNCzBN, 3CNCzBN, and 4CNCzBN with similar dihedral angles, the 2CNCzBN showed relatively longer wavelength absorption compared to the 3CNCzBN and 4CNCzBN because of the presence of cyano unit at C2 position of carbazole, which favors the linear conjugation conjugation.…”

New generations of spirobifluorene regioisomers for organic electronics: tuning electronic properties with the substitution pattern

“…In March 2019, the efficiency of the C1 position to construct high E T SBF-based host materials was demonstrated, leading to the highest performance ever reported for pure hydrocarbon hosts in blue PhOLEDs. 6 This important finding has motivated the present review. Herein, we aim to overview these new generations of SBF isomers substituted at C1, C3 or C4 and the effect of the substitution pattern in modulating their electronic properties.…”

“…Only two examples have pointed out this electronic characteristic to date. 6,76 We believe that others will come soon. Thus, it has been shown that the first oxidation wave of 1-Cbz-SBF is strongly shifted towards lower potentials (1.17 V vs SCE, Figure 14-Right) compared to its structurally related analogue fluorene-1-carbazole (1.30 V vs SCE).…”

“…2 Therefore, the SBF scaffold is found in many highly efficient OSCs especially for Organic Light-Emitting Diodes (OLED) as a fluorophore 5 or as high triplet host material for phosphors. 6 In the field of solar cells, the SBF fragment also played a key role as the widely known 2,2',7,7'-Tetrakis[N,N-di(4methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD), used as hole transporting material, is constructed on a SBF core. [7][8][9] New electronic applications taken advantages of the cross-shape geometry of the SBF fragment have also started to appear in the literature such as non-fullerene acceptors in solar cells, [10][11][12][13] spiro-fused nanographene structures 14 or ordered monolayers.…”

“…The singular geometry of the 1-substituted SBF scaffold also leads to another appealing characteristic, which should be used in the future years: the cofacial arrangement between the substituent and the facing fluorene. Indeed, when a substituent is linked at C1 of a SBF core, preliminary studies have shown 76 that there are through space interactions between this substituent and its facing fluorene (see molecular arrangement in Figure 14). Interestingly, these interactions have strong consequences on some electronic characteristics (HOMO energy level) while keeping others unaltered (E T ).…”