Efficient Triplet–Triplet Annihilation Upconversion with an Anti-Stokes Shift of 1.08 eV Achieved by Chemically Tuning Sensitizers

Abstract

A series of Pt­(II)–Schiff base complexes were synthesized as triplet sensitizers for the purpose of tuning the singlet and triplet energy levels so as to minimize energy loss during triplet–triplet annihilation (TTA) upconversion (UC). A deep-red to blue TTA-UC was achieved with an unprecedentedly large anti-Stokes shift of 1.08 eV. UC quantum yields of up to 21% (with a theoretical maximum efficiency of 50%) were observed in solution. The complexes also showed efficient UC emission in air-saturated hydrogels with a UC quantum yield up to 14.8%, which is much higher than the highest previously reported value. The low threshold excitation intensity provided by the present system offers promising potential for application in terrestrial solar energy conversion.

Multi‐Photon Excitation in Photoredox Catalysis: Concepts, Applications, Methods

“…Os II polypyridines represent another attractive option which allow the direct excitation into 3 MLCT states, and this can minimize the energy loss associated with TTA‐UC and maximize achievable anti‐Stokes shifts. Applications of such Os, Pd, or Pt sensitizers in hydrogels are of significant interest in the context of biological applications …”

Simultaneously High Upconversion Efficiency and Large Anti‐Stokes Shift by Using Os(II) Complex Dyad as Triplet Photosensitizer

“…As one of the most important parameters of TTA upconversion system, the anti‐Stokes shift is defined as the energy difference between the excitation photon and upconverted emission photon. [ 13,14 ] A large anti‐Stokes shift is very favorable for the application in photocatalytic water splitting, where the absorption is currently limited to ultraviolet light (<450 nm). [ 10 ] However, as shown in Figure , the classic TTA upconversion process involves multistep downward energy transfer processes, in which the most energies are lost in intersystem crossing (ISC) and triplet–triplet energy transfer (TTET) processes, [ 15–18 ] leading to that the reported anti‐Stokes shift is usually as small as less than 0.8 eV.…”

Multiphotonen‐Anregung in der Photoredoxkatalyse: Konzepte, Anwendungen und Methoden

“…Os II ‐Polypyridine bieten eine vielversprechende Alternative für Systeme mit großen Anti‐Stokes‐Verschiebungen, da eine direkte Anregung in 3 MLCT‐Zustände möglich ist und dadurch der Energieverlust bei der TAA‐UC minimiert werden kann. Vor allem für biologische Anwendungen sind diese Pd‐, Pt‐ und Os‐Sensibilisatoren in Hydrogelen interessant …”