Noncoherent low-power photon upconversion has been realized in solid thin films composed of an ethyleneoxide/epichlorohydrin copolymer doped with palladium octaethylporphyrin (PdOEP) and 9,10-diphenylanthracene (DPA). Selective excitation of PdOEP at 544 nm generates easily visualized DPA fluorescence in the blue with noncoherent light sources under ambient laboratory conditions. The incident excitation power dependence is quadratic in nature, exemplifying that sequential one-photon absorption by PdOEP leads to the sensitization of two triplet DPA chromophores, which in turn annihilate to produce the upconverted singlet DPA fluorescence. Time-resolved emission experiments confirm that the solid host facilitates these sequential bimolecular reactions leading to delayed DPA fluorescence; however, these processes are notably slower than the analogous photochemistry in fluid solution.
Selective low energy excitation of the metal-to-ligand charge transfer (MLCT) transition in [Ru(dmb)(3)](2+)(dmb = 4,4'-dimethyl-2,2'-bipyridine) in the presence of anthracene or 9,10-diphenylanthracene yields easily visualized upconverted singlet fluorescence resulting from triplet-triplet annihilation at low excitation power.
Double up: Photochemical upconversion by MLCT‐sensitized triplet–triplet annihilation is demonstrated (MLCT=metal‐to‐ligand charge transfer). Selective visible excitation of [Ru(dmb)3]2+ (dmb=4,4′‐dimethyl‐2,2′‐bipyridine) in the presence of anthracene efficiently produces the [4+4] cycloaddition product. This transformation traditionally requires ultraviolet light.
The sensitized triplet-triplet annihilation (TTA) of 9,10-dimethylanthracene (DMA) upon selective excitation of [Ru(dmb)3]2+ (dmb = 4,4'-dimethyl-2,2'-bipyridine) at 514.5 nm in dimethylformamide (DMF) resulted in upconverted and downconverted DMA excimer photoluminescence. The triplet excited state of [Ru(dmb)3]2+ is efficiently quenched by 11 mM DMA in DMF resulting in photon upconversion but no excimer formation. The bimolecular quenching constant of the dynamic quenching process is 1.4 x 109 M-1 s-1. At 90 mM DMA, both upconversion and downconversion processes are readily observed in aerated DMF solutions. The TTA process was confirmed by the quadratic dependence of the upconverted and downconverted emission emanating from the entire integrated photoluminescence profile (400-800 nm) of DMA measured with respect to incident light power. Time-resolved emission spectra of [Ru(dmb)3]2+ and 90 mM DMA in both aerated and deaerated DMF clearly illustrates the time-delayed nature of both types of singlet-state emission, which interestingly shows similar decay kinetics on the order of 14 mus. The emission quantum yields (Phi) measured using relative actinometry increased with increasing DMA concentrations, reaching a plateau at 3.0 mM DMA (Phi = 4.0%), while at 90 mM DMA, the overall quantum yield diminished to 0.5%. The dominant process occurring at 3.0 mM DMA is upconversion from the singlet excited state of DMA, whereas at 90 mM DMA, both upconversion and excimeric emission are observed in almost equal portions, thereby resulting in an overall broad-band visible light-emission profile.
Verdoppelt: Photochemische Upconversion durch MLCT‐sensibilisierte Triplett‐Triplett‐Aufhebung wird gezeigt (MLCT=Metall‐Ligand‐Charge‐Transfer). Die selektive Anregung von [Ru(dmb)3]2+ (dmb=4,4′‐Dimethyl‐2,2′‐bipyridin) in Gegenwart von Anthracen mit sichtbarem Licht führt effizient zum [4+4]‐Cycloaddukt. Bisher wurde für diese Umwandlung ultraviolette Strahlung benötigt.
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