Syntheses, structures and photochromism of two novel copper(II) complexes with 1,2-bis(2 0 -methyl-5 0 -(2 00 -pyridyl)-3 0 -thienyl)perfluorocyclopentene Megumu Munakata a, * , Jing Han a , Atsuhiro Nabei a , Takayoshi Kuroda-Sowa a , Masahiko Maekawa b , Yusaku Suenaga a , Nozomu Gunjima a a Department of Chemistry, Kinki University, Kowakae 3-4-1, Higashi-Osaka, Osaka 577-8502, Japan b Research Institute for Science and Technology, Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan Received 27 May 2006; accepted 30 June 2006 Available online 23 August 2006 Abstract Two novel Cu(II) complexes with 1,2-bis(2 0 -methyl-5 0 -(2 00 -pyridyl)-3 0 -thienyl)perfluorocyclopentene (BM-2-PTP) or its closed-form (closed-BM-2-PTP) were synthesized and characterized by X-ray crystallographic analysis. Both complexes are tetra-coordinated to two N atoms from distinct ligands and two Cl atoms from anions, forming 1-D polymeric structures. [Cu(BM-2-PTP)Cl 2 ](1) showed typical spectral changes as analogous Ag(I) complexes with the same ligand upon appropriate light stimulus. However, closed-BM-2- PTP displayed different photocyclization from its open-ring form upon irradiation with UV light, indicating the photogenerated closed form turned into two kinds of closed-ring isomers. Furthermore, [Cu(closed-BM-2-PTP)Cl 2 ](2) was revealed to contain two conformers by X-ray crystallographic analysis and displayed similarities in photocyclization to its free ligand. The distinct absorptions of the UV spectrum were attributed to the coexistence of two conformers in complex 2, both of which showed effective photoreactivities in the crys- talline phase. The photochromic mechanism of complex 2 is tentatively concluded as two conformers displaying independent photoreactions. Ó 2006 Published by Elsevier Ltd. Keywords: Diarylethene; Photochromism; Crystalline phase; Cu(II) complexes 1. Introduction Diarylethenes that undergo thermally irreversible and fatigue-resistant photochromic reactions are the most promising photochromic compounds among many candi- dates [1–5]. In recent years many diarylethenes have been synthesized successfully and have been found to show reversible photochromism in solution [6–10] and in the solid state [11–18]. It is known that the antiparallel confor- mation and a distance below 4 A ˚ between reactive carbons are indispensable for cyclization upon photoirradiation [19]. In solution, the two aryl groups are considered to approach each other by rotating during the photocycliza- tion. The cyclization quantum yields depend on the ratio of the two conformations. The precise mechanism of photocycloreversion remains unclear at present but a con- rotary fashion seems necessary. In crystals, molecules are regularly oriented and packed in fixed conformations, which increase the cyclization quantum yields whereas the free rotation of aryl groups are prohibited in many cases. Therefore, the photoreactivity in the crystalline phase is dependent on the conformations fixed in the crys- tal lattice. We have synthesized a series of metal complexes with photochromic ligands (cis-dbe and BM-2-PTP) and their photoreactivities have been investigated in the crystalline 0277-5387/$ - see front matter Ó 2006 Published by Elsevier Ltd. doi:10.1016/j.poly.2006.06.045 * Corresponding author. Tel.: +81 6 6721 2332x4119; fax: +81 6 6721 2721. E-mail address: munakata@chem.kindai.ac.jp (M. Munakata). www.elsevier.com/locate/poly Polyhedron 25 (2006) 3519–3525