Synthesis, Structure, and Optical Properties of an Alternating Calix[4]arene-Based Meta-Linked Phenylene Ethynylene Copolymer PATRI ´ CIA D. BARATA, 1 ALEXANDRA I. COSTA, 1 LUI ´ S F. V. FERREIRA, 2 JOSE ´ V. PRATA 1 1 Laborato ´ rio de Quı ´mica Orga ˆ nica, Departamento de Engenharia Quı ´mica and Centro de Investigac ¸a ˜ o de Engenharia Quı ´mica e Biotecnologia, Instituto Superior de Engenharia de Lisboa, Instituto Polite ´ cnico de Lisboa, R. Conselheiro Emı ´dio Navarro, 1, 1959-007 Lisboa, Portugal 2 CQFM-Centro de Quı´mica-Fı ´sica Molecular and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Te ´ cnico, Universidade Te ´ cnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal Received 30 April 2010; accepted 12 August 2010 DOI: 10.1002/pola.24302 Published online 1 October 2010 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: Novel alternating copolymers comprising bis- calix[4]arene-p-phenylene ethynylene and m-phenylene ethyny- lene units (CALIX-m-PPE) were synthesized using the Sonoga- shira-Hagihara cross-coupling polymerization. Good isolated yields (60–80%) were achieved for the polymers that show M n ranging from 1.4  10 4 to 5.1  10 4 gmol 1 (gel permeation chromatography analysis), depending on specific polymeriza- tion conditions. The structural analysis of CALIX-m-PPE was performed by 1 H, 13 C, 13 C– 1 H heteronuclear single quantum correlation (HSQC), 13 C– 1 H heteronuclear multiple bond corre- lation (HMBC), correlation spectroscopy (COSY), and nuclear overhauser effect spectroscopy (NOESY) in addition to Fourier transform-Infrared spectroscopy and microanalysis allowing its full characterization. Depending on the reaction setup, variable amounts (16–45%) of diyne units were found in polymers although their photophysical properties are essentially the same. It is demonstrated that CALIX-m-PPE does not form ground- or excited-state interchain interactions owing to the highly crowded environment of the main-chain imparted by both calix[4]arene side units which behave as insulators inhibi- ting main-chain p–p staking. It was also found that the lumines- cent properties of CALIX-m-PPE are markedly different from those of an all-p-linked phenylene ethynylene copolymer (CALIX-p-PPE) previously reported. The unexpected appearance of a low-energy emission band at 426 nm, in addition to the locally excited-state emission (365 nm), together with a quite low fluorescence quantum yield (U ¼ 0.02) and a double-expo- nential decay dynamics led to the formulation of an intramo- lecular exciplex as the new emissive species. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 5040– 5052, 2010 KEYWORDS: calixarene; fluorescence; intramolecular exciplex; meta-linked; phenylene ethynylene polymer INTRODUCTION The m-phenylene ethynylene polymers (m- PPE)s exhibit many of the interesting properties of their p- PPEs analogs, which includes photo- and electrolumines- cence, a characteristic of many conjugated polymers, although much less studies have been devoted to them. Because of the m-phenylene linkage along the polymer main chain, the inherent propensity to generate foldamers has been explored in several ways, 1 and the induction of one- handed polymer helicity been achieved. 2–4 Moreover, its potential usefulness as materials for circularly polarized photo- and electroluminescent (CPPL/CPEL) devices and chi- ral sensors may be envisioned. Several types of conjugated polymers (polythiophene, 5 polyphenylenevinylene, 6 poly- fluorene, 7 and polyphenyleneethynylene, 8 ) containing homo- chiral side chains have already been prepared for CPPL/ CPEL purposes. 5–8 Extending our previous work on the field of calix[4]arene- based PPE conjugated polymers, 9 we report here on the syn- thesis, characterization, and optical properties of a novel alternating copolymer comprising bis-calix[4]arene-p-phenyl- ene ethynylene and m-phenylene ethynylene units (CALIX- m-PPE), aiming to understand and ultimately explore the influence of the meta-connectivity on polymer properties. As will be shown, the luminescent properties of CALIX-m-PPE are genuinely distinct of those of a model compound (2) and an all-p-linked phenylene ethynylene copolymer (CALIX-p- PPE) previously reported. EXPERIMENTAL Materials and Methods Melting points were measured in sealed capillaries on a Bu ¨ chi 530 apparatus and are reported uncorrected. Fourier transform-Infrared (FT-IR) spectra were measured on a Bruker Vertex 70 as KBr pellets (transmission mode) or thin films at a resolution of 2 cm 1 . 1 H NMR (400.130 MHz) and H-decoupled 13 C NMR (100.613 MHz) spectra were collected Additional Supporting Information may be found in the online version of this article. Correspondence to: J. V. Prata (E-mail: jvprata@deq.isel.ipl.pt) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 5040–5052 (2010) V C 2010 Wiley Periodicals, Inc. 5040 WILEYONLINELIBRARY.COM/JOURNAL/JPOLA