Oxygen-Unaffected Temperature Sensing in Air-Saturated Aqueous Dispersion with Oxygen-Sensitive Luminescent Metal Complexes Encapsulated in l -Arginine-Type Silica Networks

Abstract

Bioimaging, sensing, and photonic applications of oxygen-sensitive luminophores such as near-infrared (NIR) emissive spin-flip complexes of earth-abundant chromium (CrIII) and triplet metal-to-ligand charge transfer complexes like ruthenium (RuII), osmium (OsII) or iridium (IrIII) compounds in air require efficient strategies for their complete protection from luminescence quenching by oxygen (O2). Here, we explored the applicability of our l-arginine-type sol–gel nanoparticle synthesis route developed for complete oxygen shielding of a molecular ruby-type luminophore [Cr(ddpd)2](BF4)3 (Crddpd) to a representatively chosen RuII complex [Ru(phen)3]Cl2 (Ruphen) and a RuII pyrene dyad [Ru(phen)2(phenpy)]Cl2 (Ruphenpy) with luminescence lifetimes of 1.1 μs and ∼50 μs in the absence of O2, thus confirming its versatility. Temperature-dependent steady-state and time-resolved luminescence measurements with the RuII and CrIII complexes in air- and argon (Ar)-saturated aqueous solution and encapsulated in silica nanoparticles (SiO2 NPs) prepared by the l-arginine and the classical Stöber method demonstrated the preserved temperature sensitivity of these luminophores in both silica networks. These measurements highlight the importance of complete O2 protection for reliable temperature sensing with O2-sensitive luminophores in air. These findings, together with the enhanced photostability observed for l-arginine SiO2 NPs-encapsulated Ruphen and Ruphenpy, can pave the road for many applications of O2-sensitive systems in air in the life and material sciences.