Humidity sensing properties of novel ruthenium polypyridyl complex

We report the characterization of novel ruthenium polypyridyl complex (Ru-PC) based sensor film with a thickness of 50 nm coated on a quartz substrate using a spin coating method for humidity detection. The resulting complex [Ru(L1)2(L2)] was synthesized in a one-pot reaction starting from [RuCl2(p-cymene)]2, where the ligands (L1 = 4,7-diphenyl-1,10-phenanthroline-disulfonic acid disodium salt and L2 = 4,4′-dicarboxy-2,2′-bipyridine) were characterized by NMR, mass spectrometry (MALDI), elemental analysis and UV–vis spectroscopy. The humidity adsorption and desorption kinetics of the ruthenium complex were investigated using the Quartz Crystal Microbalance (QCM) technique. The Langmuir model was used to determine adsorption and desorption rates and Gibbs free energy over the 11–97% relative humidity range. Our experimental results show that Ru-PC films have a great potential for humidity sensing applications at standard conditions (i.e. room temperature).