Metal ion induced FRET On–Off in naphthyl-pyrenyl pendent tetrahomodioxacalix[4]arene Ji Hee Jung a , Min Hee Lee a , Hyun Jung Kim a , Hyo Sung Jung a , Su Yeon Lee a , Na Ri Shin b , Kwanghyun No b, * , Jong Seung Kim a, * a Department of Chemistry, Korea University, Seoul 136-701, Republic of Korea b Department of Chemistry, Sookmyung Women’s University, Seoul 140-742, Republic of Korea article info Article history: Received 26 December 2008 Revised 10 February 2009 Accepted 12 February 2009 Available online 15 February 2009 Keywords: FRET Fluorescence Calixarenes Homooxacalixarene Copper abstract A novel tetrahomodioxacalix[4]arene (7) bearing both naphthyl- and pyrenyl-amide pendants was syn- thesized as FRET-based fluorometric sensor for Cu 2+ ion. Intramolecular FRET from the naphthalene emis- sion to the pyrene absorption affords Cu 2+ ion selectivity over other metal ions. Upon addition of Cu 2+ ion, the complex solution of 7 gave a significantly decreased pyrene acceptor emission along with an enhancement of naphthalene donor emission via FRET On–Off event. Ó 2009 Elsevier Ltd. All rights reserved. Many heavy and transition metal ions, such as Hg 2+ , Cu 2+ , Pb 2+ , and Cd 2+ , have received considerable attention because of its wide- spread use in agricultural, chemical and industrial processes, which are becoming threats to living organisms. 1 In particular, Cu(II) is an essential element playing a fundamental role in the bio- chemistry of the human nervous system, but is toxic with high concentration. 2 Thus, its accumulation in the human body affects an oxidative stress and disorders associated with neurodegenera- tive diseases, Menkes disease, Wilson disease, and Alzheimer’s dis- ease. 3 Therefore, development of the chemosensors specifically for the Cu 2+ has been greatly interesting in many fields. 4 Many chemosensors were prepared by attachment of fluoro- phore units to macrocyclic or chelating molecules. Among the macrocyclic frameworks, a class of calix[4]arene is a good candi- date for the chemosensor framework towards specific metal ion because of their characteristic cavity size or geometrically re- stricted conformation. 5 However, homooxacalix[4]arenes, having extra oxygen atoms in the macrocyclic ring, have received little attention because they can only be synthesized in relatively low yields. 6–8 Tetrahomodioxa p-tert-butylcalix[4]arene was prepared by Gutsche in 44% yield by dehydration of a bishydroxymethylated dimer of p-tert-butylphenol, which was synthesized by a multi- step reaction starting from the bromination of p-tert-butylphenol. 8 There have only been limited studies on the solution conforma- tions, solid-state structures, and on complexation behavior of homooxacalix[4]arenes. 9–12 We also previously reported that there are five conformations in tetrahomodioxacalix[4]arene with appropriate nomenclature (cone, partial cone, C-1,2-alternate, COC-1,2 alternate, and 1,3-alternate) as represented in Figure 1. 13 Recently, we also reported a solid-state structure of C-1,2-alternate N,N-diethyl tetrahomodioxacalix[4]arene tetraamide complexing 0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2009.02.083 * Corresponding authors. Tel.: +82 2 3290 3143; fax: +82 2 3290 3121 (J.S.K.). E-mail addresses: hyun@sookmyung.ac.kr (K. No), jongskim@korea.ac.kr (J.S. Kim). O O O O O O O O O O cone partial cone COC-1,2-alternate 1,3-alternate C-1,2-alternate Figure 1. Schematic representation of the five conformations of homooxacalix[4]- arenes. Tetrahedron Letters 50 (2009) 2013–2016 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet