Heavy metal-free visible-to-UV photon upconversion with over 20% efficiency sensitized by a ketocoumarin derivative

Abstract

Efficient triplet-triplet annihilation-based photon upconversion (TTA-UC) from visible to UV light without using heavy metals is still a challenging task. Here we achieve a record-high TTA-UC efficiency of 20.3% among 100% maximum by employing a ketocoumarin derivative as a triplet sensitizer, which shows strong visible absorption, weak UV absorption, and efficient intersystem crossing.

Entropy-Powered Endothermic Energy Transfer from CsPbBr3 Nanocrystals for Photon Upconversion

“…27 This efficiency is slightly higher than the previous record of visible-to-UV upconversion sensitized with perovskite NCs, 14 although it still lags behind the efficiencies achieved with molecular sensitizers. 28,29 To understand the remarkable TTA-UC performance, we measured the relevant energy transfer processes using timeresolved spectroscopy (see the SI for experimental details). Figure 3a presents the time-resolved photoluminescence (TR-PL) traces of NC448 and NC448-PTA in a time window of 10 ns; the decay of the latter is clearly strongly accelerated.…”

Spatially Controlled UV Light Generation at Depth Using Upconversion Micelles

“…Annihilators for TTA-UC are usually small organic molecules like acenes, whereas sensitizers be a range of materials such as metallic complexes, thermally activated delayed fluorescence (TADF) molecules, and inorganic nanoparticles. 20,27,28 For UC emission in the UV, a range of sensitizer and annihilator pairs for both blue-to-UV UC [33][34][35][36][37][38][39][40][41][42][43] and green-to-UV UC 44 demonstrate the flexibility of materials options, excitation wavelengths, and emission ranges available to accommodate distinct requirements for different light-driven applications. Yet despite this apparent versatility, sensitizers and annihilators used for UV light generation via TTA-UC are usually incompatible with aqueous environments.…”

“…In addition to the aforementioned iridium complexes, we selected two pure organic sensitizers, 3,3'-carbonylbis(7-diethylaminocoumarin) (CBDAC) 43 and 2,4,5,6-tetra(carbazol-9-yl)benzene-1,3-dicarbonitrile (4CzIPN), 36 to investigate the scope of materials compatible with this encapsulation method. We encapsulated annihilators with different UV emission ranges: pyrene, 41 1,4-bis((triisopropylsilyl)ethynyl)naphthalene (TIPS-Nph), 39,43 and 2,5-Diphenyloxazole (PPO). 40 We note that PPO emits photons at wavelengths shorter than 350 nm, which is a particularly attractive range for photochemical reactions.…”

“…Slightly red-shifted UC emissions were observed from pyrene and TIPS-Nph and are attributed to molecular aggregation. 41,43 Overall, this incredible flexibility to mix-and-match sensitizers and annihilators in micelles presents opportunities to meet the diverse requirements of a wide range of applications. S4.…”