Carbazole-based aromatic amines having oxetanyl groups as materials for hole transporting layers

doi:10.1016/j.synthmet.2007.05.015

Synthetic Metals

Volume 157, Issues 13–15, July 2007, Pages 529-533

https://doi.org/10.1016/j.synthmet.2007.05.015 Get rights and content

Abstract

Several oxetane-functionalized aromatic amines have been synthesized by the multi-step synthetic rout. Full characterization of their structure by nuclear magnetic resonance and mass spectroscopy as well as IR spectrometry is presented. The synthesized materials were examined by various techniques including differential scanning calorimetry, thermogravimetry, UV spectrometry, electron photoemission and time of flight techniques. The electron photoemission spectra of the layers showed the ionisation potentials of 5.24–5.67 eV. Time-of-flight hole drift mobility in amorphous layers of bisphenol Z polycarbonate containing 33 wt. % of the electroactive materials ranges from 10⁻⁸ to 10⁻⁶ cm²/Vs at high electric fields.

Introduction

Electroactive and photoactive organic materials capable of forming amorphous films are known for various applications such as displays [1], [2], photovoltaic cells [3], organic transistors [4] and electrophotographic photoreceptors [5]. Amorphous organic materials are divided into two categories. One is low-molar-mass molecules; the devices are generally fabricated by vacuum-deposition. The other is polymers; the devices are fabricated by the casting or spin-coating methods. Among the low-molar-mass derivatives, triphenylamine and carbazole compounds are the most extensively used as hole transport materials because they are easily oxidized to form stable radical cations [6], [7], [8]. However, the latter low-molecular-weight derivatives have some problems such as the lack of the morphological and thermal stability as well as rather high ionization potentials [9], [10], [11].

In this work, we have designed and synthesized new carbazole-based condensed aromatic systems having polymerizable oxetane moieries. The new aromatic structures demonstrate better charge injection properties than those of derivatives containing pedant carbazole groups. Such materials can be photopolymerized directly in thin film to afford charge transporting layers. On the other hand, the oxetanyl-functionalized derivatives can be used for preparation of hole transporting polymers by cationic polymerization.

Section snippets

Instrumentation

¹H NMR spectra were recorded using Varian Unity Inova (300 MHz) apparatus. Mass spectra were obtained on a Waters ZQ 2000 spectrometer. FTIR spectra were recorded using Perkin-Elmer FT-IR System. UV spectra were measured with a Spectronic Genesys™ 8 spectrometer. Fluorescence (FL) spectra were recorded with a MPF-4 spectrometer. Differential scanning calorimetry (DSC) measurements were carried out using a Bruker Reflex II thermosystem. Thermogravimetric analysis (TGA) was performed on a Netzsch

Results and discussion

The synthetic rout towards the condensed aromatic amines with (photo)polymerizable oxetanyl groups (5–7) is shown in Scheme 1. The diiodo derivative 2 as key material was synthesized from commercially available 9H-carbazole (1) by Tucker iodination [16] with KI/KIO₃ in acetic acid. 3,6-Diiodo-9H-carbazole (2) was alkylated with 1,6-dibromohexane under basic conditions to give 3,6-diiodo-9-(6-bromohexyl)carbazole (3). Compound 3 was then treated with 3-hydroxymethyl-3-ethyl-oxetane in two-phase

Acknowledgements

Financial support of this research by the Lithuanian Science and Studies Foundation is gratefully acknowledged. We thank habil. Dr. V. Gaidelis for the help in ionisation potential measurements.

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Carbazole-based aromatic amines having oxetanyl groups as materials for hole transporting layers

Abstract

Introduction

Section snippets

Instrumentation

Results and discussion

Acknowledgements

Synth. Met.

Synth. Met.

Synth. Met.

Synth. Met.

Synth. Met.

Appl. Phys. Lett.

Appl. Phys. Lett.

Chem. Mater.

Adv. Mater.

Chem. Mater.

Macromol. Rapid. Commun.

J. Mater. Chem.

Electrophotography