Photon Upconversion in a Molecular Lanthanide Complex in Anhydrous Solution at Room Temperature

Abstract

Molecular photon upconversion luminescence was observed from an ion-associated complex of an erbium chelate of 2-thenoyltrifluoroacetone and a near-infrared-emitting cyanine dye in anhydrous solution at room temperature. In the complex erbium was sensitized by the organic antenna dye excited at 808 nm. The result was characteristic erbium emission at 510−565 nm with second-order dependence on the excitation power, suggesting a dye-sensitized energy transfer upconversion mechanism. Compared to inorganic upconverting nanoparticles, the organic molecular dye-sensitized complexes are expected to offer higher molar absorptivity, smaller well-defined size, and simpler addition of functional groups.

Thermodynamic Programming of Erbium(III) Coordination Complexes for Dual Visible/Near‐Infrared Luminescence

“…[31] As the ionic radius of the target Er 3 + cation is significantly smaller than that of Eu 3 + ,wee xploited compact N-methyl substituents to minimize spatial expansioni nl igands L4-L6,t ogether with the connection of terminal alkyl substitution of in-Scheme2.Erbium-based coordination complexes exhibiting linear upconversion processes through the ETU mechanism. X-ray crystal structures are shown for [CrErCr(L1) 3 ](CF 3 SO 3 ) 9 [23] and [YbEr(L3) 6 (DME) 2 ] [25] (color code: C = gray,N= dark blue, O = red, F = light blue).C hemical structures deduced from spectroscopic data recorded in solution are depicted for [IR-806] [Er(tta) 4 ] [22] and [(L2Er)F(L2Er)] + . [24] Scheme3.Synthesis of 2,6-bis(5,5'-disubstituted-benzimidazol-2-yl)pyridine ligands L4-L6.…”

“…To the best of our knowledge, the unambiguous implementation of ESA in molecular complexes under reasonable incident pump intensities (i.e., below 1 kW cm −2 ) is currently unknown, and the few successful molecular erbium‐centered upconverters reported so far exploit the ETU mechanism as found in [IR‐806][Er(tta) 4 ] (use of a polyaromatic sensitizer), [CrErCr( L1 ) 3 ] 9+ (use of a d‐block sensitizer), [( L2 Er)F(Er L2 )] + , and [YbEr( L3 ) 6 (DME) 2 ] (use of f‐block sensitizers, Scheme ) . Beyond some classical optimization of the sensitization in the latter complexes maximizing NIR absorption cross sections, the ultimate induction of visible Er‐centered emission, for instance, the green Er( 4 S 3/2 → 4 I 15/2 ) signal, while at least one long‐lived intermediate excited state relay of lower energy is available, for instance Er( 4 I 13/2 ), represents a major impediment for the implementation of successful linear piling up of photons in these molecular systems. Looking at erbium chemistry, the latter requirement for multiple (at least dual) emission is commonly fulfilled in solid‐state samples and nanoparticles, and upconversion is therefore common in doped solids .…”

“…X‐ray crystal structures are shown for [CrErCr( L1 ) 3 ](CF 3 SO 3 ) 9 and [YbEr( L3 ) 6 (DME) 2 ] (color code: C=gray, N=dark blue, O=red, F=light blue). Chemical structures deduced from spectroscopic data recorded in solution are depicted for [IR‐806][Er(tta) 4 ] and [( L2 Er)F( L2 Er)] + …”

“…[18] Linear upconversion was significantly improved af ew years later by the demonstrationt hat the indirects ensitization may help greatlyi nf eeding the pertinent long-lived erbiumcentered excited states (energyt ransfer upconversion, ETU), [19] and ETU is currently exploited for engineering functional solid materials and nanoparticles. [20] To the best of our knowledge,t he unambiguous implementation of ESA in molecular complexes under reasonable incident pump intensities (i.e.,b elow 1kWcm À2 )i sc urrently unknown, [21] and the few successful molecular erbium-centered upconverters reported so far exploit the ETU mechanism as found in [IR-806][Er(tta) 4 ]( use of ap olyaromatic sensitizer), [22] [CrErCr(L1) 3 ] 9 + (use of ad -block sensitizer), [23] [(L2Er)F(ErL2)] + , [24] and [YbEr(L3) 6 (DME) 2 ]( use of f-blocks ensitizers, Scheme 2). [25] Beyonds omec lassical optimization of the sensitization in the latter complexesm aximizing NIR absorption cross sections, [22] the ultimatei nduction of visible Er-centered emission, for instance,t he green Er( 4 S 3/2 !…”

Probing the nature of upconversion nanocrystals: instrumentation matters

“…As a result, it is deemed that the radiative energy transfer plays a trivial role in the energy transfer process. 232 A Förster resonance energy transfer model, suitable for the situation between molecular donors and acceptors, has been utilized to study the efficiency of energy transfer between UC nanocrystals and suitable energy acceptors in close proximity (eqn (12)). 230 To achieve broadband excitable UC nanocrystals, recent studies have shifted the focus of research on developing UC nanocrystals for use as energy acceptors.…”