Table S1 . Calculation particle size and mass particle size (o-NP) hexagonal prism h = 38.8 nm = 38.8 × 10 -7 cm l,r = 33.6 nm = 33.6 × 10 -7 cm volume = ((3√3)/2) × r 2 × h = 1.14 × 10 -16 cm 3 density 1 NaYF 4 = 4.2 g/cm 3 mass of each UCNP = 4.79 × 10 -16 g Table S2 . Calculation of loading using absorbances in the UV region of the spectra of 3a, 3b, 1a-NP and 1b-NP a A 3a THF (282-300 nm) = 0.47255 A 3b CH2Cl2 (282-289 nm) = 0.39173 ε 3a THF (282-300 nm) = 45005 M -1 cm -1 ε 3a CH2Cl2

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... 89 nm) = 37308 M -1 cm -1 A 1a-NP THF (274-287 nm) = 0.46107 A 1b-NP CH2Cl2 (275-282 nm) = 0.40818 C 1a-NP = A 1a-NP /(ε 3a × l) = 1.02 × 10 -5 M C 1a-NP = A 1b-NP /(ε 3b × l) = 1.09 × 10 -5 M MW 1a = 739.9 gmol -1 MW 1b = 661.8 gmol -1 V = 3.05 mL, n 1a = 3.23 × 10 -8 mol, mass 1a = 2.39 × 10 -5 g = 1.95 × 10 16 molecules V = 3.05 mL, n 1b = 3.32 × 10 -8 mol, mass 1b = 2.20 × 10 -5 g = 2.04 × 10 16 molecules Electronic Supplementary Material (ESI)