Near-Infrared-to-Visible Photon Upconversion Sensitized by a Metal Complex with Spin-Forbidden yet Strong S₀–T₁Absorption

Abstract

Near-infrared (NIR)-to-visible (vis) photon upconversion (UC) is useful for various applications; however, it remains challenging in triplet-triplet annihilation-based UC, mainly due to the energy loss during the S1-to-T1 intersystem crossing (ISC) of molecular sensitizers. In this work, we circumvent this energy loss by employing a sensitizer with direct S0-to-T1 absorption in the NIR region. A mixed solution of an osmium complex having a strong S0-T1 absorption and rubrene emitter upconverts NIR light (λ = 938 nm) to visible light (λ = 570 nm). Sensitizer-doped emitter nanoparticles are prepared by re-precipitation and dispersed into an oxygen-barrier polymer. The obtained composite film shows a stable NIR-to-vis UC emission based on triplet energy migration (TEM), even in air. A high UC quantum yield of 3.1% is observed for this TEM-UC system, expanding the scope of molecular sensitizers for NIR-to-vis UC.

Kinetically controlled crystal growth approach to enhance triplet energy migration-based photon upconversion

“…The present kinetically controlled crystallization concept for improving donor dispersibility in acceptor crystals would be widely applicable to a variety of chromophore combinations, including the recently developed precious metal-free systems 25,45,46 and NIRto-visible UC systems. [12][13][14][15]47,48 For further improvement of the current method, we consider that the key is to suppress the formation of defect sites that deactivate the triplet excitons. 28 The development of approaches to circumvent this issue is under way in our laboratory.…”

Spin–Orbit Charge‐Transfer Intersystem Crossing (ISC) in Compact Electron Donor–Acceptor Dyads: ISC Mechanism and Application as Novel and Potent Photodynamic Therapy Reagents

“…The most commonly used method to enhanceI SC is based on the introduction of heavy atoms into the chromophores. However,l imitations do exist for this strategy.F or instance, the dark toxicity is ag reat concern for photodynamic therapy (PDT) with these heavy atom-containingm olecules; [10,19] moreover,the triplet lifetime in these systems is generally shortened owing to strong heavy atom effect, [20,21] which is detrimental to the intermoleculare lectron or energy transfer initiated by the photoexcited photosensitisers (PSs). Compared with shortlived PSs, long-lived triplet PSs have been provedt ob em ore efficient in oxygen sensing, [22] photocatalysis [23] and PDT.…”

Near‐Infrared Optogenetic Genome Engineering Based on Photon‐Upconversion Hydrogels

“…To circumvent this energy loss,n ew triplet sensitization routes with semiconductor nanocrystals or molecules showing singlet-to-triplet (S-T) absorption have been developed. [4] Our group previously utilized the direct S-Tabsorption derived from the triplet metal-to-ligand charge transfer ( 3 MLCT) transition of osmium complexes in organic solvents (Supporting Information, Figure S1 b). [5] Thet riplet energy level of aS-T sensitizer (Os(bptpy) 2 2+ )was tuned for ab lue emissive acceptor,2 ,5,8,11-tetra-tert-butylperylene (TTBP), and the Os(bptpy) 2 2+ -TTBP mixed solution showed aN IR-to-blue TTA-UC with al arge anti-Stokes shift of 0.97 eV.…”