Novel 2,7-Linked Carbazole Trimers as Model Compounds for Conjugated Carbazole Polymers

Abstract

In this paper we present a new synthesis for N-alkylated 2,7-dibromocarbazoles, from which 2,7-linked carbazole trimers have been synthesized by Suzuki cross coupling. The compounds were characterized regarding their thermal, optical, and electrochemical properties and compared to analogous fluorene trimers, which also have been prepared by Suzuki reactions. The carbazole and fluorene trimers exhibit thermal stabilities of more than 300 °C and are able to form molecular glasses. Only one of the carbazole trimers is crystalline. Both carbazole and fluorene trimers exhibit a bright blue fluorescence with a maximum at 393 nm and show similar absorption characteristics. Cyclovoltammetric experiments revealed the electrochemical stability of the fluorene trimers. Their HOMO and LUMO levels are at -5.6 and -2.5 eV, respectively. In contrast to the fluorenes, the 2,7-linked carbazole trimers showed nonreversible oxidations in the CV experiments.

A Molecular Glass for Deep‐Blue Organic Light‐Emitting Diodes Comprising a 9,9′‐Spirobifluorene Core and Peripheral Carbazole Groups

“…[55,56] The oxidation peaks at relatively high potentials of 1.04 and 1.08 V are attributed to oxidation of the trimer fluorene units in the backbone of the compounds. [57,58] The oxidation-onset potentials for these compounds (0.79 V for TCPC-6 and 0.81 V for TCPC-4) are significantly lower than that for Mod I (1.01 V). The highest occupied molecular orbital (HOMO) energy levels of TCPC-6 and TCPC-4 estimated from the onset potentials are -5.47 and -5.49 eV, respectively, with respect to the energy level of the Fc reference.…”

Synthesis, Optical, and Electrochemical Properties of the High‐Molecular‐Weight Conjugated Polycarbazoles

“…The fresh yellow film became dark green and insoluble in THF by increasing the applied potential up to 0.8 V. For polymer 7, the film showed one oxidation peak at 0.86 V in the first redox cycle and no peak in the successive cycles in the range of 0-1.3 V. Similar to polymer 6, the yellow film of polymer 7 also turned dark green and insoluble in THF by increasing the potential applied up to 1.1 V. The unstability of polymers 6 and 7 was probably due to that the 3,6-positions of the carbazole ring in 2,7-linked carbazole polymers were highly activated and could form the radical-cations of carbazolic units. [20][21][22] The carbazole polymers formed cross-linking structures during the CV measurements. [23] Taking À4.8 eV as the HOMO level for the ferrocene/ferrocenium redox system, HOMO level of À5.33 and À5.47 eV were calculated for polymers 6 and 7, respectively.…”

Novel carbazole phenoxy-based methacrylates to produce high-refractive index polymers

“…Strohriegl worked extensively with the amidation of polymethacrylates and polyacrylates, including the incorporation of pendant carbazole groups [8][9][10]. His recent work investigated a novel synthesis for N-alkylated 2,7-dibromocarbazoles, using Suzuki cross coupling to produce 2,7-linked carbazole trimers [11].…”