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

Abstract

Visible-to-UV upconversion shorter than 340 nm was achieved in organic solvents and the solvent dependent efficiency and photostability were elucidated.

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

“…[39,40] The obtained η UC was more than twice larger than the previous record of 8.2% for the heavy metal-free vis-to-UV TTA-UC. [26] The tripletmediated UC mechanism was confirmed by a millisecond-scale decay of the UC emission (Fig. S3, ESI †).…”

“…Since the first report of vis-to-UV TTA-UC in 2006, [11] various donor-acceptor combinations have been reported, but the efficiency had remained low for a long time. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Our group has achieved the highest TTA-UC efficiency η UC of 20.5% (theoretical maximum: 100%) in 2020, which was twice as high as the previous record. [28] This is due to the use of an Ir-coumarin complex Ir(C6) 2 (acac) with strong absorption in the visible region and weak absorption in the UV region as a donor, as well as the discovery of an acceptor 1,4bis((triisopropylsilyl)ethynyl)naphthalene (TIPS-Nph) with high TTA and fluorescence efficiencies and a T 1 energy low enough to be sensitized by Ir(C6) 2 (acac).…”

“…Several examples of heavy metalfree vis-to-UV TTA-UC have been reported, but even the most efficient one showed a low TTA-UC efficiency of 8.2%. [20][21][22][23][24][25][26][27] In addition, the threshold excitation intensity I th at which half of the maximum UC efficiency is obtained is so high that it exceeds 1 W cm −2 in many cases. It is strongly desired to realize TTA-UC with both high efficiency and low I th without using heavy metals.…”

Ionic‐Liquid‐Based, Sustainable Wavelength‐Shifting Materials for Energy Conversion: A Minireview

“…Subsequently, UV-UC to a shorter wavelength than 340 nm is achieved in various solvents, including an IL by Murakami et al recently. [45] It is observed that UC-QYs and the photostability of sensitizer 10-butyl-2-chloro-9(10 h)-acridinone under continuous photoirradiation varies from solvent to solvent. It is found that UC-QYs are mainly governed by the solvent polarity, which varied the relative T 1 energy-level matching between the sensitizer and emitter, 2,6-di-tertbutyl naphthalene due to the solvatochromic shift imposed on sensitizer.…”

“…To develop non-volatile TTA-UC systems, earlier approaches have to introduce rubbery polymers or non-volatile liquids [5,24,[40][41][42][43][44][45][46][47][48] as matrices for the translational diffusion of molecules in the triplet excited state. Though translational molecular diffusion is certainly restricted in these viscous media, high intensity of excitation light is essential for getting upconverted light which is undesirable.…”