Polypyridylpropyne-Pd and -Pt porphyrin coating for visualization of oxygen pressure Tsuyoshi Hyakutake 1 , Hiroyuki Taguchi 1 , Hirotaka Sakaue 2 and Hiroyuki Nishide 1 * 1 Department of Applied Chemistry, Waseda University, Tokyo 169 8555, Japan 2 Japan Aerospace Exploration Agency, Tokyo 182 8522, Japan Received 25 January 2008; Accepted 21 February 2008 Poly[1-trimethylsilyl-1-propyne-co-1-(3-pyridyl)propyne] 1 was prepared both as a polymer-ligand of a palladium porphyrin (PdOEP) and of a platinum porphyrin (PtTFP) and as a highly gas- permeable polymer matrix of the porphyrin. The porphyrin acted as a phosphorescence probe which could be quenched with oxygen and sense the oxygen partial pressure. 1 gave a smooth and tough coating with a thickness of ca.2 mm which homogeneously involved the porphyrin. The porphyrin-1 coatings displayed strong red-colored phosphorescences (the emission maximum at 670 and 650 nm for PdOEP and PtTFP, respectively), and their intensity significantly decreased with an increase in the oxygen partial pressure on the coating. The high oxygen-quenching efficiency or the high oxygen pressure sensitivity of the porphyrin’s phosphorescence was observed even at cryogenic temperature. Aggregation of the porphyrin was suppressed in the coating by ligation of the porphyrin with the nitrogenous residue of 1 to significantly reduce spatial noise in the phosphor- escence measurement or the oxygen-pressure sensing. PtTFP-1 was coated on the surface of a delta wing model. The oxygen-pressure distribution on the coated model was successfully visualized in a cryogenic wind tunnel test. Copyright # 2008 John Wiley & Sons, Ltd. KEYWORDS: polymer–metal complex; poly(trimethylsilylpropyne); porphyrin; luminescence; oxygen sensor INTRODUCTION Knowing the oxygen concentration or oxygen partial pressure is significant in various fields of science and engineering such as aerodynamics and medical studies, and environmental analyses. 1–6 For example, the measurement of pressure upon a body and channel surface is a common requirement for aerodynamic studies: researchers usually use electric oxygen sensors based on semi-conductor technology. However, such electric sensors have limitations. 5 One of these is in their spatial resolution, being a millimeter-sized ‘‘point’’ sensor; the electric sensors are not capable of obtaining ‘‘field’’ information with a micro- and submicro-meter-sized spatial resolution. A variety of optical oxygen sensors based on luminescen- ce-quenching of the organic dye molecules dispersed in polymer matrices were recently developed to analyze the oxygen partial pressure distribution upon a body surface with a high spatial resolution. 4–9 The oxygen-pressure sensitive luminescent coatings often employed metallopor- phyrin molecules. 10–15 Luminescence from the organic dye (in this paper, phosphorescence from porphyrin) under UV irradiation is sometimes quenched by oxygen molecule and the quenching behavior usually obeys the Stern–Volmer equation. Measuring the luminescence (phosphorescence) intensity could lead to oxygen concentration or pressure sensing. Some optical oxygen sensors based on the phosphorescence-quenching of porphyrins had been studied by dispersing the porphyrins in polymer matrices such as silicone and polystyrene. 15 Our group has successfully applied poly(1-trimethylsilyl-1-propyne) (2) to the coating matrix of a porphyrin. 10,12,13 It has been known that the gas permeability of 2 is the highest among conventional polymers and is maintained even at low temperature because of its amorphous glassy structure with a large frozen volume. 16,17 Such a high gas-permeation property of the matrix polymer resulted in a high oxygen sensitivity of the optical oxygen sensor. However, the polymer coating prepared by simply mixing the porphyrin with 2 often formed an aggregation of the porphyrin in the polymer coating that resulted in a spatial noise and/or a decreasing phosphorescent intensity. Pyridine derivatives are known to act as a ligand of metalloporphyrins, and copolymers of pyridine group (pyridyl)-bearing monomers have been prepared and studied as a polymer-ligand of cobalt- and iron- porphyrins. 18–20 However, there has been no previous report of a polymer-ligand for palladium- and platinum- porphyrins and on a pyridyl-bearing poly(trimethylsilyl- propyne). POLYMERS FOR ADVANCED TECHNOLOGIES Polym. Adv. Technol. 2008; 19: 1262–1269 Published online 28 April 2008 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/pat.1122 *Correspondence to: H. Nishide, Department of Applied Chem- istry, Waseda University, Tokyo 169 8555, Japan. E-mail: nishide@waseda.jp Contract/grant sponsor: Japan Aerospace Exploration Agency and the Global COE program ‘‘Chemical Wisdom’’ at Waseda University from MEXT, Japan. Copyright # 2008 John Wiley & Sons, Ltd.