Fluorescence is a relatively faster phenomenon as compared with phosphorescence because of spontaneous emission of energy from s1 to s0. if it chooses the nonradiative path from s1 to a triplet state, t1 results in the slower decay of the process to reach the ground state s0. during this time interval, quenchers such as molecular oxygen can be involved in phosphorescence emission of the fluorophore. the process of quenching of the excited fluorophore in the triplet state by molecular oxygen can be one of the three different possible pathways such as energy transfer, electron transfer, and simple physical deactivation.
for the transition-metal complexes such as ruthenium, the energy-transfer mechanism is the most possible mechanism and it is dominated by the molecular collision thus limited by the diffusion of the quencher and is given by the stern−volmer relation. on the basis of the data derived from previous reports, a hydrophobic fluorophore of the ruthenium-based metal-ligand complex was selected for our sensing applications. to avoid the photobleaching effect of the fluorophore, a suitable substrate material has to be chosen and this provided broad adaptability to the specific needs. a fluorophore can be tethered or encapsulated onto a substrate material, and it can be in the form of a thin film or particle.