Visible‐to‐UV Photon Upconversion in Nanostructured Chromophoric Ionic Liquids

Abstract

Visible‐to‐ultraviolet (vis‐to‐UV) triplet‐triplet annihilation based photon upconversion (TTA‐UC) is achieved in a non‐volatile chromophoric ionic liquid (IL) for the first time. A novel IL is synthesized by combining UV‐emitting anion 4‐(2‐phenyloxazol‐5‐yl)benzenesulfonate (PPOS) and trihexyltetradecylphosphonium cation (P66614). The nanostructured organization of chromophoric anions is demonstrated by synchrotron X‐ray and optical measurements. When the IL is doped with a triplet sensitizer tris(2‐phenylpyridinato)iridium(III) (Ir(ppy)3), the visible‐to‐UV TTA‐UC with a relatively low threshold excitation intensity of 61 mW cm−2 is achieved. This is due to a large triplet diffusion coefficient in the IL (1.4×10−7 cm2 s−1) as well as a high absorption coefficient 15 cm−1 and a long PPOS triplet lifetime of 1.55 ms, all implemented in the condensed IL system. This work demonstrates the unique potential of ILs to control chromophore arrangements for desired functions.

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

“…[32] Moreover, The UC emission intensity did not change after one hour of continuous laser irradiation, indicating the high stability of the current system (Figure 2 c). On the other hand, when the previous best acceptor PPO [21,27,[30][31][32] was combined with Ir(C6) 2 (acac) in THF, no upconverted emission was observed (Supporting Information, Figure S7).…”

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

“…[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.…”

“…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.…”

TIPS-Naphthalene for Efficient Visible-to-UV Photon Upconversion under Sunlight and Room Light

“…33,34 This ηUC is the highest value for vis-to-UV TTA-UC ever reported and twice higher than the previous record (10.2%). 32 On the other hand when the previous best acceptor PPO 21,27,[30][31][32] was combined with Ir(C6)2(acac) in THF, no upconverted emission was observed ( Figure S6).…”

“…While the conversion of visible light (vis, > 400 nm) to ultraviolet light (UV, < 400 nm) is crucial for artificial photosynthesis and photocatalytic environmental cleanup, the efficiency of vis-to-UV TTA-UC (UC) at solar irradiance has been limited. [20][21][22][23][24][25][26][27][28][29][30] Relatively high vis-to-UV UC values of 5.2% and 10.2% have been observed by using semiconductor nanocrystals as donor and 2,5-diphenyloxazole (PPO) as acceptor. 31,32 However, their threshold excitation intensities (Ith), at which half of the maximum UC is obtained, were much higher (ca.…”