Highly soluble perylene dyes: Synthesis, photophysical and electrochemical characterizations Gu ¨ lsah Tu ¨ rkmen * , Sule Erten-Ela, Siddik Icli * Ege University, Solar Energy Institute, 35100 Bornova-Izmir, Turkey article info Article history: Received 29 January 2009 Received in revised form 10 May 2009 Accepted 12 May 2009 Available online 11 June 2009 Keywords: Perylene dyes Swallow-tailed substituted perylene diimides Photophysical properties Electrochemical characterization Soluble dyes Fluorescent dyes abstract Highly soluble perylene diimide derivatives with symmetrical and unsymmetrical secondary, tertiary alkyl side chains were synthesized and their photophysical properties, redox potentials and thermal stabilities were measured and compared with previously reported 1-pentylhexyl substituted swallow- tailed perylene diimide. Diasteroisomers of the novel, unsymmetrical swallow-tailed substituted perylene diimide compound could not be detected using low temperature NMR spectroscopy. The novel dyes were soluble in a range of organic solvents indicating potential for photo-electronic applications and photocatalytic reactions. Two dyes were not only soluble in organic solvents but also showed solubility in aqueous media as the hydrochloride salt, thus offering potential use in biological applications. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Perylene diimides are inexpensive, readily available compounds. Moreover, perylene derivatives are highly fluorescent, and they exhibit singlet energy transfer over unusually long distances [1,2]. Perylene diimides have attracted great interest as a result of their unique optical and photophysical properties. These dyes have found applications in light-harvesting systems, organic electronic systems (solar cells, organic field-effect tran- sistors etc), fluorescent solar collectors etc [3–9]. Different synthetic methods, properties and novel developments in per- ylene dye chemistry have been comprehensively summarized by Langhals [10]. Soluble and highly fluorescent perylene dyes can be obtained by the attachment of t-butylaryl or long-chain secondary alkyl groups (swallow-tailed substituents) at the nitrogen atoms [11,12]. Synthesis of swallow–tailed substituted perylene diimides have been reported previously in the literature [12–14]. In particularly 1-hexylheptyl substituted swallow-tailed perylene diimide has been the subject of different investigations in numerous publications [15–18]. Solving of the solubility problem has induced development of functional perylene derivatives. Required proper- ties can be adopted to these functional perylene dyes by controlling of their internal interactions [19,20]. The solubility of perylene dyes is important in respect to their use in applications with high efficiency. Indeed, in our previous study we have obtained high performance in OFET (organic field- effect transistor) applications using highly soluble 1-pentylhexyl and 1-butylpentyl substituted perylene diimides [7]. In this study, we have synthesized novel, highly soluble perylene diimides which can be used in different applications such as organic electronic applications or photocatalytic reactions. High solubilities could be obtained with different bulky, branched substituents. Dye 2 has been synthesized by attachments of the unsymmetrical 1-butylhexyl alkyl side chains to perylene dianhy- dride so it contains two stereogenic centers. NMR spectra of this compound have been performed at low temperatures (40  C, 10  C, 0  C, 25  C) in order to able to detect rotational isomers. Photophysical properties, thermal stabilities, redox potentials of the synthesized compounds have been determined and compared with each other and previously reported 1-pentylhexyl substituted swallow-tailed perylene diimide. Their solubilities have been tested in different solvents. We have also investigated different fluores- cent properties of dye 4. * Corresponding authors. Tel.: þ90 232 3886025; fax: þ90 232 3886027. E-mail addresses: gtrkmen@yahoo.com (G. Tu ¨ rkmen), s_icli@yahoo.com (S. Icli). Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig 0143-7208/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2009.05.014 Dyes and Pigments 83 (2009) 297–303