UV Light Generation and Challenging Photoreactions Enabled by Upconversion in Water

Abstract

Sensitized triplet-triplet annihilation (sTTA) is the most promising mechanism for pooling the energy of two visible photons, but its applications in solution were so far limited to organic solvents, with a current maximum of the excited-singlet state energy of 3.6 eV. By combining tailor-made iridium complexes with naphthalenes, we demonstrate blue-light driven upconversion in water with unprecedented singlet-state energies approaching 4 eV. The annihilators have outstanding excited-state reactivities enabling challenging photoreductions driven by sTTA. Specifically, we found that an arylbromide bond activation can be achieved with blue photons, and we obtained full conversion for the very energy-demanding decomposition of a persistent ammonium compound as typical water pollutant, not only with a cw laser but also with an LED light source. These results provide the first proof-of-concept for the usage of low-power light sources for challenging reactions employing blue-to-UV upconversion in water, and pave the way for the further development of sustainable light-harvesting applications.

Discovery of Key TIPS‐Naphthalene for Efficient Visible‐to‐UV Photon Upconversion under Sunlight and Room Light**

“…Highly efficient TTA‐UC from visible/near‐infrared to visible light has been achieved through the great efforts of many groups [1–19] . On the other hand, the TTA‐UC efficiency ( η UC ) from visible light (vis, λ >400 nm) to ultraviolet light (UV, λ <400 nm) at solar irradiance has been low [20–30] . The vis‐to‐UV TTA‐UC is very important for photocatalysis and purification of the indoor environment, so it is strongly expected to improve its efficiency.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] On the other hand, the TTA-UC efficiency (h UC ) from visible light (vis, l > 400 nm) to ultraviolet light (UV, l < 400 nm) at solar irradiance has been low. [20][21][22][23][24][25][26][27][28][29][30] The vis-to-UV TTA-UC is very important for photocatalysis and purification of the indoor environment, so it is strongly expected to improve its efficiency. Relatively high vis-to-UV h UC values of 5.2 % and 10.2 % have been observed by using semiconductor nanocrystals as donor and 2,5-diphenyloxazole (PPO) as acceptor.…”

Visible-to-ultraviolet (<340 nm) photon upconversion by triplet–triplet annihilation in solvents

“…For PPO, 2,3-butanedione (biacetyl) has often been used as the sensitizer. 43,46,49 As far as we surveyed, except for our previously published open patent documents 53 on which this study is based and a recent report using iridium complex sensitizers in water, 54 both of which were UV-UC to wavelengths shorter than 340 nm, the shortest emission peak wavelength reported for UV-UC is 343-344 nm using terphenyl as the emitter. 47,50 Therefore, UV-UC with emission maxima shorter than 340 nm has not been well explored thus far.…”

Red-to-Blue Photon Upconversion Enabled by One Dimensional CdTe Nanorods

“…Photon upconversion (UC) via triplet-triplet annihilation (TTA) in organic semiconductors is an efficient way to generate higher energy photons at relatively low fluences. 1 TTA-UC could prove to be useful in a multitude of applications, such as photocatalysis, [2][3][4] optogenetics, 5 photovoltaics, 6,7 or bioimaging. 8 In lieu of metal-organic complexes with exchange energy losses on the order of hundreds of meVs, 9 recently inorganic semiconductor materials including bulk perovskites [10][11][12][13] and spherical semiconductor quantum dots (QDs) have emerged as efficient triplet sensitizers for the TTA-UC process.…”