Liquid PEG and PEGDA as Protective Matrices for TTA‐UC Functioning in Air and Their Application in Information Encryption

Photochemical deoxygenation offers a promising solution to the oxygen sensitivity issue in Triplet-triplet annihilation upconversion (TTA-UC). This study utilized polyethylene glycol (PEG)-200 and polyethylene glycol diacrylate (PEGDA)-575 as solvents and singlet oxygen scavengers for TTA-UC conducted in air. The upconversion efficiency of Pt(OEP)/DPA in aerated PEG-200 is similar to that in nitrogen-saturated PEG-200. Prolonged 532 nm light irradiation causes a PEGDA-575 solution of Pt(OEP)/DPA to undergo photoinitiated polymerization via homomolecular TTA, leading to a reduction in DPA's upconversion emission and an increase in Pt(OEP)'s phosphorescence. These results enabled the development of a high-level information encryption platform using the direct-writing method with Pt(OEP)/DPA/PEGDA-575 or Pt(OEP)/DPA/PEGDA-575/PEG-200 ink. The information is only readable under certain lighting conditions or at specific times and can be erased by exposure to light.