Synthesis of L-prolinol substituted novel optically active phthalocyanines Hüseyin Karaca a, b , Serdar Sezer a , Cihangir Tanyeli a, * a Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey b Department of Chemistry, Sakarya University, 54187 Sakarya, Turkey article info Article history: Received 16 October 2010 Received in revised form 30 November 2010 Accepted 7 December 2010 Available online 15 December 2010 Keywords: L-prolinol Optically active phthalocyanine Phthalocyanine Water soluble Chiral peripheral unit CD spectroscopy abstract The novel optically active Pc-4 (neutral) and Pc-5 (ionic), zinc(II) phthalocyanines having four N-benzyl protected L-prolinol unit were synthesized. L-prolinol has binucleophilic character and can be anchored to phthalonitrile derivative from both nitrogen and oxygen atoms. In order to overcome this problem and to enhance the solubility of phthalonitrile (S)-(-)-3 and the target phthalocyanines, the nitrogen atom of L-prolinol was first protected with benzyl chloride. All the compounds were characterized by 1 H and 13 C NMR, MALDIeTOF MS, IR, UVevis, and Circular Dichroism (CD) spectroscopy. Pc-4 is highly soluble in most common organic solvents, whereas ionic Pc-5 is soluble in water. The CD results showed that the chiral information was transferred from the peripheral chiral L-prolinol side chains to the phthalocyanine chromophore at the molecular level. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Phthalocyanines (Pcs) have unique properties due to their conjugated core units which have found widespread application as dyes and catalysts [1]. Moreover, in the years, they have attracted increasing interest for their application in the construction of molecular devices. For example they have found utility in many popular areas of research such as photodynamic therapy (PDT) [2e4], organic photovoltaic (OPV) devices [5e9], and organic field- effect transistors (OFETs) [10]. Although a wide range of studies on the synthesis, properties and applications of many phthalocyanines has received more research interest than porphyrins, chiral phthalocyanines have received less attention than chiral porphyrins. However, optically active Pcs are more available than porphyrins in some respects. For instance, Pcs are prone to co-facial aggregation and may form helical superstructures. In addition, to analyze their circular dichroism (CD), Pcs are superior to porphyrins, since the Q-band is much more intense. The studies on the chiral Pcs have emerged over the last few decades. In particular, after 1990, Kobayashi and co-workers [11e 16] made very valuable contributions in this emerging field [17e21]. In this study, we report the synthesis and the photophysical evaluation of a novel family of optically active phthalocyanines with L-prolinol peripheral units (Fig. 1). The reason for choosing this class of Pcs is that the bulky and ionic peripheral substitutions on Pcs core enhance solubility in organic and aqueous media and control the aggregation behavior [1,22]. In our synthetic strategy, the N-benzyl protected L-prolinol unit was first anchored to the core scaffold of phthalocyanines and subsequent cyclo- tetramerization afforded the optically active target ZnPcs. Since the nitrogen atom of L-prolinol unit has the capacity to form quaternary ammonium salt, the neutral L-prolinol substituted Pc was easily transformed into the ionic Pc, which is soluble in water. To the best of our knowledge, L-prolinol type chiral peripheral units have never been utilized before for the construction of optically active phtha- locyanines. The combined structure of L-prolinol and Pc may be a valuable candidate as an organocatalyst in the application of asymmetric transformation reactions. 2. Experimental 2.1. General All experiments were carried out in pre-dried glassware (1 h, 150  C) under an inert atmosphere of argon. The following reaction solvents were distilled from the indicated drying agents: DMAE (CaH 2 ), DMF (CaH 2 ). Melting points were obtained on a Thomas * Corresponding author. Tel.: þ90 312 210 32 22; fax: þ90 312 210 32 00. E-mail address: tanyeli@metu.edu.tr (C. Tanyeli). Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig 0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2010.12.003 Dyes and Pigments 90 (2011) 100e105