A bis-cyclometalated iridium complex as a benchmark sensitizer for efficient visible-to-UV photon upconversion

To resolve the biggest problem in visible-to-UV photon upconversion based on sensitized triplet–triplet annihilation—the quenching of upconverted fluorescence by sensitizers—we discovered a superior sensitizer with less UV absorption intensity that enables highly efficient, low-power (0.78 mW cm−2) visible-to-UV upconversion.