Photochemically deoxygenating gels for triplet-triplet annihilation photon-upconversion performed under air

For an efficient triplet-triplet annihilation photon upconversion (TTA-UC) process, matrices in which sensitizers and emitters are dispersed should not only allow molecular diffusions but also protect triplet excited states from oxygen-quenching. In this work, two photochemically deoxygenating gels, a poly(N-vinyl-2-pyrrolidone) (PVP) gel and a limonene gel, were prepared for TTA-UC performed under air. These two gels are optically transparent in the visible region and can serve as a scavenger for sensitized singlet oxygen. For the green-to-blue couple of platinum(II) octaethylporphyrin (Pt(OEP)) and 9,10-diphenylanthracene (DPA), under air, the bimolecular quenching rate constants were 6.73 × 10⁸ dm³ mol^-1 s^-1 for the PVP gel and 1.54 × 10⁹ dm³ mol^-1 s^-1 for the limonene gel, and the upconversion quantum yields were 9.1% and 1.9% in PVP and limonene gels, respectively. As matrices, the PVP gel can be employed in NIR-to-yellow, red-to-cyan, green-to-blue and blue-to-violet TTA-UC systems operating under air. TTA-UC systems of Pt(OEP)/DPA in PVP or limonene gels showed strong upconverted emission under air with non-coherent light of low optical power density as the excitation source.