Enhanced luminescence oxygen sensing property of Ru(II) bispyridine complexes by ligand modification

Phenylethynylene containing polypyridyl ruthenium (Ru) complexes 1 and 2 were prepared using chemistry-on-complex approach. The luminescent lifetimes of these complexes were extended by more than 2-fold (tau = 1.8 mu s for complex 1) when compared to the reference complex 3 (i.e. Ru(Phen)(bpy)(2), tau = 0.8 mu s). Based on DFT/TDDFT calculations, we propose that (LLCT)-L-3/(MLCT)-M-3 mixed states are the emissive triplet states of 1 and 2. Luminescence oxygen sensitivity of the complexes are improved with extension of the lifetimes, e.g.I-0/I-100 = 15.4 for complex 3, but I-0/I-100 = 36.8 was observed for the complex 1 in MeCN solution (I-0 is the emission in N-2 and I-100 is the emission intensity under O-2 atmosphere). O-2 sensitivity of the complexes were also studied in polymers IMPES-C, PES-C and polyvinyl chloride (PVC). The IMPES-C sensing film demonstrated very short response time and recovery time (3.4 and 7.5 s, respectively), which is ideal for practical O-2 sensors. Modified Stern-Volmer equation and the two-sites model were used to fit the luminescent O-2 sensing data. We found that with tuning the luminescence lifetimes, the luminescence O-2 sensitivity of the Ru complexes (quenching constant, k(SV)) can be improved by up to 20-fold. (C) 2010 Elsevier B.V. All rights reserved.