Molecular light-upconversion: we have had a problem! When excited state absorption (ESA) overcomes energy transfer upconversion (ETU) in Cr(iii)/Er(iii) complexes

Abstract

Nine-coordinate [ErN9] or [ErN3O6] chromophores found in triple helical [Er(L)3]3+ complexes (L corresponds to 2,2’,6’,2”-terpyridine (tpy), 2,6-(bisbenzimidazol-2-yl)pyridine (bzimpy), 2,6-diethylcarboxypyridine (dpa-ester) or 2,6-diethylcarboxamidopyridine (dpa-diamide) derivatives), [Er(dpa)3]3- (dpa is the 2,6-dipicolinate dianion)...

Ligand-Sensitized Near-Infrared to Visible Linear Light Upconversion in a Discrete Molecular Erbium Complex

“…A continuous NIR diode laser excitation at 801 nm of [ L6 Er­(hfa) 3 ] + (5 × 10 –4 M in acetonitrile at room temperature) does not exhibit a well-defined downshifted NIR Er­( 4 I 13/2 → 4 I 15/2 ) emission (Figure S11), but two upconverted emission bands can be detected in the visible region centered at 542 nm (18 450 cm –1 ) and 522 nm (19 157 cm –1 ), which are unambiguously assigned to the erbium-centered Er­( 4 S 3/2 → 4 I 15/2 ) and Er­( 2 H 11/2 → 4 I 15/2 ) transitions, respectively (Figure a). The corresponding log­( I up ) – log­( P ) plot ( I up = intensity of upconverted emission, and P = incident pump intensity) reveals a linear dependence of the emission on the incident pump intensity with a slope of 1.51(4), which is compatible with the successive absorption of two NIR photons prior to reach the Er 3+ -centered emissive excited levels (Figure b and Scheme ), which is one of the characteristics of linear light upconversion processes. , …”

Metal-Based Linear Light Upconversion Implemented in Molecular Complexes: Challenges and Perspectives

“…A deliberate design of molecular complexes programmed for single-center ESA light upconversion under reasonable excitation intensities can be traced back to the synthesis of triple-stranded erbium complexes with polyaromatic tridentate ligands L possessing increased complexities and sizes (Figure a). ,− The resulting triple-helical complexes [Er­(DPA) 3 ] 3– , [Er L 3 ] 3+ (L = DPA-R, R-tpy, and R-bzimpy), and [GaErGa­(dipy-bzimpy) 3 ] 9+ (Figure b) are quantitatively formed in acetonitrile at millimolar concentrations and display dual downshifted microsecond infrared Er­( 4 I 13/2 → 4 I 15/2 ) emissions at 1520–1540 nm (τ Er,obs |1⟩ ≈ 2–6 μs, Figure a,b) and nanosecond visible Er­( 4 S 3/2 → 4 I 15/2 ) emission at 542 nm (τ Er,obs |2⟩ ≈ 38–40 ns, Figure a) under standard ligand excitation. ,, Upon near-infrared excitation of the Er­( 4 I 9/2 ← 4 I 15/2 ) transition at 801 nm and using P = 3–25 W·cm –2 , all these complexes display the expected one-photon downshifted infrared Er­( 4 I 13/2 → 4 I 15/2 ) band at 1520–1540 nm, together with two-photon upconverted green Er­( 4 S 3/2 → 4 I 15/2 ) luminescence with low, but structurally tunable quantum yields at room temperature in acetonitrile (5.5 × 10 –11 ≤ ϕ A up (ESA) ≤ 1.7 × 10 –9 at P = 25 W·cm –2 , Figures b and c). ,, Having k A,rad 2→0 , P , τ Er,obs |1⟩ , τ Er,obs |2⟩ , and ϕ A up (ESA) in hand, eq gives access to the intrinsic erbium-centered luminescence quantum yields, ϕ Er = k Er,rad 2→0 τ Er,obs |2⟩ , and to η Er up (ESA) = ϕ Er up (ESA)/ϕ Er = [(λ p / hc )­σ Er 1→2 P ]­τ Er,obs |1⟩ , from which the nonexperimentally accessible absorption cross sections σ Er 1→2 of the Er­( 2 H 11/2 , 4 S 3/2 ← 4 I 13/2 ) ESA process can be deduced (Figure c) . The associated decadic absorption coefficients ε Er 1→2 = (2.6 × 10 20 )­σ Er 1→2 cover the 1–50 M –1 ·cm –1 range and exceed by at least 2 orders of magnitude the efficiency of the Er­( 4 I 9/2 ← 4 I 15/2 ) ground-state absorption (GSA) process (0.07 ≤ ε Er 0→1 ≤ 0.12 M –1 ·cm –1 ).…”

Recyclable optical bioplastics platform for solid state red light harvestingviatriplet–triplet annihilation photon upconversion

“…Photon upconversion (PUC) is a process of transforming low-energy photons into high-energy photons. [1][2][3] Among the known PUC processes, [1][2][3][4][5][6][7][8] triplet-triplet annihilation photon upconversion (TTA-UC) has an advantage over energy transfer upconversion (ETU), excited-state absorption (ESA), and photon avalanche (PA), due to the operation at flexible spectral ranges, and at low excitation intensities. [9][10][11] TTA-UC occurs in an ensemble of chromophores, wherein a sensitizer after absorbing low energy generates triplet states, followed by triplet energy transfer (TET) to the annihilator via a Dexter energy transfer mechanism.…”