Synthesis, structure, and optical properties of an alternating calix[4]arene‐based meta‐linked phenylene ethynylene copolymer

Abstract

AbstractNovel alternating copolymers comprising bis‐ calix[4]arene‐p‐phenylene ethynylene and m‐phenylene ethynylene units (CALIX‐m‐PPE) were synthesized using the Sonogashira‐Hagihara cross‐coupling polymerization. Good isolated yields (60–80%) were achieved for the polymers that show Mn ranging from 1.4 × 104 to 5.1 × 104 gmol−1 (gel permeation chromatography analysis), depending on specific polymerization conditions. The structural analysis of CALIX‐m‐PPE was performed by 1H, 13C, 13C–1H heteronuclear single quantum correlation (HSQC), 13C–1H heteronuclear multiple bond correlation (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 inhibiting main‐chain π–π staking. It was also found that the luminescent 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 (ϕ = 0.02) and a double‐exponential decay dynamics led to the formulation of an intramolecular exciplex as the new emissive species. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010