Mediated Generation of Conjugate Acid by UV and Blue Sensitizers with Upconversion Nanoparticles at 980 nm

NIR and UV exposure of systems comprising upconversion nanoparticles (UCNP) based on NaYF(4):Tm/Yb@NaYF(4), a sensitizer absorbing either in the blue or UV region, and an onium salt with weak coordinating anion resulted in formation of conjugate acid (con‐H(+)). That was namely Ivocerin (di(4‐methoxybenzoyl)diethylgermane), ITX (2‐iso‐propyl thioxanthone), anthracene, pyrene, rubrene, camphore quinone, and a strong fluorescent coumarin (1,1,6,6,8‐pentamethyl‐2,3,5,6‐tetrahyhdro‐1H,4H‐11‐oxa‐3a‐aza‐benzo[de]anthracene‐10‐one). Quantification occurred by treatment with Rhodamine B lactone whose color switched to intensive red after photolytic formation of con‐H(+). Exposure with a NIR laser at 980 nm resulted in less con‐H(+) compared to 395 nm where all sensitizers absorb radiation. UCNP did not mainly interfered formation of con‐H(+). The different rates obtained in both experiments responsibly explain the failure and success to initiate polymerization of epoxides applying ether 980 nm or 395 nm excitation, respectively.