Optical gas sensing based on alkyl-π functional molecular liquids

Luminescent organic molecules (LOMs) are commonly utilized in chemical sensing and optoelectronic devices with a solid support or matrix. Nevertheless, their performance is frequently limited by adverse phenomena such as undesirable aggregation, concentration quenching, and photodegradation of LOMs. In this study, we employ a strategy to isolate and wrap a phosphorescent Pt(II)-porphyrin core by bulky yet flexible branched alkyl chains, resulting in a solvent-free liquid at room temperature that demonstrates excellent properties for sensing oxygen (O2) gas. Compared to reference material composed of Pt(II)-tetraphenylporphyrin and a highly gas-permeable polymer matrix, our Pt(II)-porphyrin liquid shows comparable sensitivity (I0/I100 = ~90), better linearity, and greater photostability in its O2-responsive phosphorescence. This is attributed to the high homogeneity and gas solubility of liquids as well as the shielding of π-core units by bulky alkyl chains. The liquid nature of the materials allows for ratiometric sensing, where the compatibility of a phosphorescent Pt(II)-porphyrin liquid (O2-sensitive) and a fluorescent pyrene liquid (O2-insensitive) enables reproducible monitoring of O2 concentration without specific calibration. Indeed, these results highlight the significant benefits of core-isolated luminescent liquids in diverse sensing applications.