Optical and electrochemical properties of polyether derivatives of perylenediimides adsorbed on nanocrystalline metal oxide films Mahmut Kus a,b, * , Özgül Hakli a,c , Ceylan Zafer a , Canan Varlikli a , Serafettin Demic a , Serdar Özçelik d , Siddik Icli a, * a Ege University, Solar Energy Institute, 35040 Bornova, Izmir,Turkey b Department of Chemistry, Mugla University, Mugla,Turkey c Department of Chemistry, Celal Bayar University, Manisa,Turkey d Izmir Institute of Technology, Urla-Izmir,Turkey a r t i c l e i n f o Article history: Received 21 January 2008 Received in revised form 6 May 2008 Accepted 10 May 2008 Available online 22 May 2008 PACS: Organic semiconductors, 72.80.L Electrochromism,78.20.J Electrochromic devices, 85.60.P Thin films optical properties 78.66 Keywords: Perylenediimide n-doping material Metal oxide film Electrochromism a b s t r a c t We report optical and electrochemical properties of polyether derivatives of perylenedii- mides (PDIs) thin films formed in various materials (semiconductor, insulator, amorphous and self-assembly). Perylenediimides adsorbed on nanocrystalline TiO 2 (NT) nanocrystal- line alumina (NA), amorphous silicon (PS) and neat self-assemblied (SA)films were prepared and characterized based on spectroscopic, electrochemical, spectro-electrochem- ical techniques. The absorption and fluorescence spectra of PDIs in chloroform exhibit vib- ronic features. The fluorescence quantum yields ( U f ) of PDIs with end amino substituents in chloroform solutions are over 0.95, while the quantum yield of triethoxyphenyl substi- tuted PDI U f value is 0.024 in solution. Optical spectroscopy proves that PDIs in metal oxide thin films form aggregated type complexes. An electrochromism, a color change from red to blue/violet, is observed on metal oxide films, that indicates existence of mono and dian- ion forms of PDIs.Reversibility of electrochemical reductions in NT film depends on the scanning rate. However, electrochromism in NA films is stable and reversibility is indepen- dent from scanning rate. Stable mono and diaionic species are formed on NA films. SA films show broad absorption peaks during the voltammetric scan. On the other hand,the first reduction onset potentials of PDIs are almost equal to the onset potential of capacitive cur- rent of TiO 2 which lead to low efficiency in dye-sensitized solar cells. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Perylenediimides(PDIs) represent one of the most widely studied classes of organic semiconductorswith possible applications in photovoltaic cells, electrophotog- raphy,laser dyes and organic light-emitting diodes [1–8]. They are inexpensive and easily accessible materials also attractive owing to intense, high fluorescence quantum yield and general photostability but suffer from poor solu- bility in common organic solvents. Synthesis of highly sol- uble PDIs is very important for the preparation of their thin films to be used in photoelectronic applications [9–11]. They exhibit singlet energy transfer over unusually long distances [12,13]. Most organic conducting materials can be described as p-type semiconductors; in contrast, PDIs are described as n-type semiconductors in which the major charge carriers are in their conduction band. Such materi- als are employed as electron accepting materials in all or- ganic photovoltaic solar cells [7,8,14–18]. PDIs show two reversible electrochemical reductions at modest potentials, 1566-1199/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.orgel.2008.05.009 * Corresponding authors. Address: Selcuk University, Departmentof Chemical Engineering, 42100 Konya,Turkey. Tel.: +90 332 2232095; fax: +90 332 2410635 (M. Kus), Tel.: +90 232 3886025; fax: +90 232 3886027 (S. Icli). E-mail addresses: mahmut_kus@yahoo.com (M. Kus), siddik.icli@ ege.edu.tr (S. Icli). Organic Electronics 9 (2008) 757–766 Contents lists available at ScienceDirect Organic Electronics j o u r n a l h omepage: w w w . e l s e v i e r . c o m / l o c a t e / o r g e l