Chemical influences on the luminescence of ruthenium diimine complexes and its response to oxygen

Abstract

Different luminescent, hydrophillic ruthenium diimine cationic complexes are rendered soluble in the hydrophobic medium of a plasticised polymer through ion-pair coupling with a hydrophobic anion, such as tetraphenyl borate. Based on this approach, a number of different oxygen sensitive films, i.e., luminescent, thin plastic films which respond to oxygen — the latter quenches the luminescence — were prepared, using the polymer, cellulose acetate, plasticised with tributyl phosphate. Of the resultant thin oxygen sensitive films tested, the one containing the luminescent ion-pair ruthenium (II) tris(4,7-diphenyl-1,10-phenanthroline) ditetraphenyl borate, [Ru(dpp) 2+ 3(Ph 4B −) 2], was found to be the most sensitive, and its response characteristics were subsequently studied as a function of plasticiser content, temperature and stability in use, and with age. The major response characteristics, i.e., film sensitivity towards oxygen and response and recovery times, depend very strongly upon the overall level of plasticiser present in film; the film is more sensitive and faster in response and recovery the greater the level of plasticiser employed. Thus, the response of the film towards oxygen can be tuned by varying the level of plasticiser in the film. Film sensitivity towards oxygen is largely independent on temperature, whereas its response and recovery times decrease with increasing temperature ( E a = −10.3 ± 0.4 kJ mol −1). The sensitivity of a typical luminescent film is very stable when used continuously over a 24-h period, decreases by ca. 20% with age when stored at ambient temperature over a period of 29 days, but very little over the same period of time when stored in the freezer section of a fridge.