Elsevier

Synthetic Metals

Volume 129, Issue 3, August 2002, Pages 281-283
Synthetic Metals

Synthesis and characterization of organic photorefractive glass

https://doi.org/10.1016/S0379-6779(02)00083-8Get rights and content

Abstract

Bifunctional molecule, which possesses photoconductive and electrooptic properties in one molecule, was synthesized as a new photorefractive material. Carbazole as a photoconductive moiety was covalently bound to thiophene derivative as an electrooptic chromophore via a flexible alkyl chain. The sample prepared from the mixture of bifunctional molecule (89 wt.%), 2,4,7-trinitro-9-fluorenone (1 wt.%) and ethylcarbazole (10 wt.%) showed good photorefractive property. The 50 μm thick film showed the maximum diffraction efficiency of 65% at 70 V/μm, corresponding to a refractive index modulation (Δn) of ca. 4.5×10−3.

Introduction

Photorefractive effect refers to a spatial modulation of the refractive index in a material due to the light-induced redistribution of charge [1], [2]. It has been drawn much attraction due to the potential applications in optical information processing and holographic data storage [2]. To possess photorefractive property, the material is required to possess both photoconductivity and electrooptic activity. In general photorefractive materials are prepared by combining all required functional moieties (i.e., photoconducting moiety and electrooptic chromophore) to form a single molecule or more commonly in guest–host composite. Among the many organic photorefractive materials reported to date, photoconducting polymers doped with chromophore have been extensively studied, due to their remarkable photorefractive properties [3], [4], [5]. However, this guest–host system often lacks the device stability arising from the limited compatibility between nonpolar photoconducting polymer and polar chromophore [3], [6]. The phase separation of composite seriously limits the optical property and lifetime of photorefractive material.

Designing the multifunctional system can alleviate the phase separation problem. Recently, organic photorefractive glasses based on bifunctional molecules, which provide electrooptic property and charge transport in a single molecule, have been reported [7], [8], [9], [10]. In addition to the much improved shelf lifetime of device, the low molar mass organic glasses have shown the high photorefractive properties, comparable to the highly efficient guest–host composites.

Herein, we report new low-molecular weight bifunctional molecule based on carbazole and optically anisotropic thiophene derivative. The current paper focuses on the synthesis and characterization of a new organic photorefractive glass.

Section snippets

Experimental

New bifunctional molecule, 2-(5-{4-[6-(9-ethyl-9H-carbazol-3-yl)-6-methoxy-hexyl]-piperazin-1-yl}-thiophen-2-yl ethylene)-malononitrile (hereafter referred to as CZ-C6-THDC) was synthesized using the reaction scheme, as shown in Fig. 1. The chemical structure of the new bifunctional molecule was characterized by 1H NMR spectrometry (Varian, INOVA, 400 MHz). 1H NMR (CDCl3): δ 8.09 (d, J=7.6 Hz, 1H), 8.00 (s, 1H), 7.49–7.21 (m, 7H), 6.09 (d, J=4.4 Hz, 1H), 4.37 (q, J=7.2 Hz, 2H), 4.26 (t, J=6.8 Hz,

Results and discussion

We designed bifunctional molecule in which the photoconducting carbazole moiety is linked to the electrooptic chromophore via a flexible aliphatic chain. As shown in Fig. 1, carbazole unit was chosen because of its well-known photoconducting property. 2-Piperazinly-5-thienylmalononitrile was selected as an electrooptic moiety since thiophene derivative has showed the good performance as a chromophore for photorefractive application, due to its high optical nonlinearity [12], [13]. In our

Acknowledgements

The financial support of this work from Creative Research Initiatives is gratefully acknowledged.

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