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Optoelectronics/Displays??

Light-emitting anthracene liquid developed for foldable CEs

Posted: 26 Jun 2013 ?? ?Print Version ?Bookmark and Share

Keywords:anthracene molecule? full-colour luminescence device?

A research team headed by Takashi Nakanishi, a principal researcher of the NIMS organic materials group, polymer materials unit, has developed a full-colour tunable luminescent liquid material featuring excellent light stability based on an anthracene molecule, which is a general organic fluorescent dye.

In the development of full-colour display monitors, mobile devices and other electronic devices, organic molecular and polymer materials are essentially important, as they offer advantages such as light weight, flexibility and printability. However, in virtually all cases, the light-emitting organic molecular materials developed until now have had difficulties to demonstrate their inherent luminescent performance due to various problems, which include low photostability (durability to prevent discolouration or decolourisation under photoirradiation) and aggregation of molecules in the coating process.

Moreover, from the viewpoint of production of flexible devices, materials should be free of deterioration of the continuous emissive layer, even when subjected to excessive bending and folding. On the other hand, development of organic molecular materials that enable simple, low-cost manufacture of full-colour luminescence devices, in comparison with individual synthesis of organic molecular materials that display various luminescent colours, is also desired.

Full-colour luminescence panels

Figure 1: Full-colour luminescence panels under ultraviolet (365nm) irradiation by adjustment of the nonvolatile blue-emitting anthracene liquid (left: photo) in the material.

The team led by Nakanishi developed a blue-emitting liquid material that is free of aggregation among adjacent anthracene parts, has a melting point of about -60C, and is thermally stable up to about 300C, by attaching highly flexible branched alkyl chains around an anthracene core moiety, which is a fluorescent general dye molecule. This material is a low-viscosity liquid with viscosity of roughly 0.3Pa-s at room temperature and is a blue-emitting with an absolute fluorescence quantum yield of nearly 55 per cent and photostable more than 5-10 times longer lifetime than that of commercially-available anthracene dyes. Furthermore, because other luminescent dye molecules can be doped homogeneously in this liquid, it was found that full-colour luminescence tuning is available assisted by up to 96 per cent fluorescence resonance energy transfer (FRET) of dyes by single blue-light (365nm) excitation.

In this research, a blue-emitting anthracene liquid with excellent photostability was synthesised, and a liquid material that displays high quality full-colour luminescence and precise luminescence tuning by the facile operation of doping the liquid with other dyes was developed. Since the nonvolatile liquid material developed in this work can be coated on the surface of various substrates, production of organic multi-colour devices with stable single colour excitation can be expected. A continuous active emitting layer can be maintained, without breaking or interruption even when bent and folded, which is a favourable property for the development of foldable flexible devices.





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