A new blue light emitting and electrochromic polyfluorenederivative for display applicationsBuket Bezgin Carbasa, Demet Asilb, Richard H. Friendb,⇑, Ahmet M. Önala,⇑aDepartment of Chemistry, Middle East Technical University, 06800 Ankara, TurkeybCavendish Laboratory, University of Cambridge, JJ Thomson Ave, Cambridge CB3 0HE, UKa r t i c l ei n f oArticle history:Received 25 October 2013Accepted 2 December 2013Available online 15 December 2013Keywords:PolyfluoreneElectrochromismLight emitting diodeConjugated polymera b s t r a c tA novel blue emitting and electro-chromic conjugated copolymer based on 9,90dioctylflu-orene (F8) and spiro(fluorene-9,90-xanthene) (SFX) has been prepared. Optical, photophys-ical and electrochemical characterizations are given for the synthesized polymer;poly[spirofluorene-co-9,90dioctylfluorene] P(F8-SFX). Switching of the corresponding poly-mer between yellow and purple states is demonstrated, and blue emission with Commis-sion Internationale de L’Eclairage (CIE) coordinate at (0.19, 0.15) is obtained from PLEDdevice. The addition of a thin polymer interlayer ((F8)0.5–(TFB)0.5) is further investigatedto maintain color purity. Furthermore, all polymer electrochromic device (ECD) based onP(F8-SFX) and poly(ethylene dioxythiophene) (PEDOT) was constructed. Spectroelectro-chemistry and switching ability of the device were also investigated by UV–visspectroscopy.? 2013 Elsevier B.V. All rights reserved.1. IntroductionDisplay applications have been in progress ever sincethe discovery of electrochromic and light emitting technol-ogies. Although many organic and inorganic materialsexhi-bit the property of electrochromism, especially, conductingpolymers have been visualized as one of the most favoredelectrochromesindevices,smartwindows,opticaldisplays,mirrors and camouflage materials [1–4] due to their prom-ising advantages, such as processability over large surfaces,high optical contrast ratio, multicolors with the same mate-rial, high redox stability and long cycle life with low re-sponsetime,whencomparedtotheinorganicelectrochromes [5–13]. Thus many research groups havebeen working hard attempting to design and synthesize ofpolymeric electrochromics based on conjugated polymers[14]. In the case of light-emitting devices, modifying thecomposition of the polymers at the molecular level is alsovery important for color-tuning purposes. It is possible tomake large area displays with polymeric materials by sim-ple solution processable methods such as spin coating andlarge area printing, e.g. ink-jet printing. The key advantagesof this technology are low-cost and environmentally-friendly manufacture together with the possibility to up-scale to very large substrates. Nonetheless, that kind ofapplications (ECDs and LEDs) possesses some intrinsic lim-itations during daily use depending on the light conditions.For example, the usage of back or front light source to visu-alize the image in dark conditions is necessary for ECDs andthis causes the consumption of extra power [15]. Con-versely, the visibility of the image gets difficult in brightambient conditions for light emitting diodes (LEDs) [16].Therefore, the materials with dual electrochromic and elec-troluminescent properties have been attracting a greatamount of attention [15,17] in order to pave the way fordisplays which operates at reflective and emissive statessimultaneously. Dual type displays however requires care-ful design of materials and engineering of the devices.Therefore, it is very important to pick up the electrochro-mism and light emission in the same material. However,1566-1199/$ - see front matter ? 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.orgel.2013.12.003⇑Corresponding authors. Tel./fax: +90 3122103188.E-mail addresses: rhf10@cam.ac.uk (R.H. Friend), aonal@metu.edu.tr(A.M. Önal).Organic Electronics 15 (2014) 500–508Contents lists available at ScienceDirectOrganic Electronicsjournal homepage: www.elsevier.com/locate/orgel
