Supporting information for. Photon Upconverting Liquids: Matrix-Free Molecular Upconversion Systems Functioning in Air

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1 Supporting information for Photon Upconverting Liquids: Matrix-Free Molecular Upconversion Systems Functioning in Air Pengfei Duan, Nobuhiro Yanai,* and Nobuo Kimizuka* Department of Chemistry and Biochemistry, Graduate School of Engineering, Center for Molecular Systems (CMS), JST CREST, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka , Japan. 1. Experimental Section Materials. All reagents and solvents for synthesis were used as received without further purification. Platinum(II) octaethylporphyrin (PtOEP) was purchased from Aldrich and were used as received. Synthesis of 1. The hydroxyl group of 2-octyl-1-dodecanol was converted to bromo derivative by using N-bromosuccinimide (NBS) and triphenylphosphine (PPh 3 ) as the bromination reagents in dichloromethane at 0 ºC for 2h. The product 9-(bromomethyl) nonadecane was purified by chromatography (hexane) over silica gel. In a typical synthesis of 1, a mixture of 9-(bromomethyl) nonadecane (6 mmol), 9,10-bis(3,5-dihydroxyphenyl)anthracene (1 mmol) and potassium carb (8 mmol) in anhydrous N,N-dimenthylformamide (DMF, 30 ml) was heated to 80 ºC for 20 h. After S1

2 the reaction, solvent was removed under reduced pressure. The resultant residue was extracted with dichloromethane and washed several times with brine and water, and then dried over anhydrous Na 2 SO 4. Evaporation of the organic layer under reduced pressure followed by column chromatography (n-hexane/dichloromethane) over silica gel yielded the pure 1 liquid (yield: 53%). 1 H NMR (300 MHz, CDCl 3 ): δ = (m, 24H), (m, 128H), 1.53 (m, 4H), 3.84 (d, J = 6 Hz, 8H), (m, 6H), (m, 4H), (m, 4H). MALDI-TOF-MS, (dithranol matrix): calculated for C 106 H 178 O ; found [M + ]. Elemental analysis, calculated for C 106 H 178 O 4 : C, 83.95; H, 11.83; found: C, 83.97; H, Synthesis of TPP-COOEH. A mixture of tetrakis(4-carboxyphenyl)porphyrin (79 mg, 0.1 mmol), 1-bromo-2-ethylhexane (0.16 mg,0.6 mmol) and potassium carbonate (0.11 mg, 0.8 mmol) in anhydrous DMF (15 ml) was heated to 80 ºC for 20 h. After the reaction, the reaction solvent was removed under reduced pressure. The resultant residue was extracted with dichloromethane and washed several times with brine and water, and then dried over anhydrous Na 2 SO 4. Evaporation of the organic layer under reduced pressure followed by column chromatography (n-hexane/dichloromethane) over silica gel yielded the pure purple solid TPP-COOEH. Yield: 0.11 mg, 81%. Synthesis of 2. To a mixture of TPP-COOEH (50 mg, 0.04 mmol) in benzonitrile (30 ml), PtCl 2 (106 mg, 0.4 mmol) was added under Ar atmosphere. The resulting mixture was refluxed for about 7 h, and the reaction was stopped when the fluorescence of the free-base porphyrin disappeared. After the removal of benzonitrile, the residue was purified by column chromatography (silica gel, n-hexane/dichloromethane). Yield: 52 mg, 90 %. 1 H NMR (300 MHz, CDCl 3 ): δ = (m, 24H), (m, 32H), (m, 4H), (m, 8H), (m, 8H), (m, 8H), 8.73 (s, 8H). MALDI-TOF-MS, (dithranol matrix): calculated for C 80 H 92 N 4 O 8 Pt ; found [M + ]. Elemental analysis, calculated for C 80 H 92 N 4 O 8 Pt: C, 67.07; H, 6.47; N, 3.91; found: C, 66.88; H, 6.37; N, Characterization. 1 H NMR (300 MHz) spectra were measured on Bruker DRX-300 spectrometer using TMS as internal standard. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was performed on a Bruker Autoflex-III. Elemental analysis was conducted at the Elemental Analysis Center, Kyushu University. XRD analysis was conducted on a RIGAKU smart-lab with a copper K-alpha source. SAXS analysis was carried out using a Rigaku MicroMax-007HF with a copper K-alpha source. Luminescence spectra were measured by using a PerkinElmer LS 55 fluorescence spectrometer. The samples were excited with an incidence angle of 45º to the quartz cell surface and the fluorescence was detected along the normal. Emission spectra were recorded with excitation wavelength of 375 nm or 510 nm. UV-vis spectra were recorded on a JASCO V-670 spectrophotometer. The absolute quantum yields were calculated using a Hamamatsu C G instrument. Time-resolved fluorescence lifetime measurements were carried out by using time-correlated single photon counting lifetime spectroscopy system, HAMAMATSU Quantaurus-Tau C (for fluorescence lifetime)/c (for delayed luminescence lifetime). The quality of the fit has been judged by the fitting parameters such as χ 2 (<1.2) as well as the visual inspection of the residuals. Differential scanning calorimetry (DSC) was performed in a Seiko Electronics SSC-5200 S2

3 instrument. The rheology experiments were carried out using an Anton Paar MCR-302 Rheometer at 25 ºC. The upconversion luminescence emission spectra were recorded on Otsuka Electronics MCPD-7000 instrument with the excitation source using an external, adjustable 532 nm semiconductor laser (0-140 mw). Measurement of Upconversion Luminescence Quantum Efficiency. The upconversion luminescence quantum efficiency (Φ UC ) of the upconverting liquid was determined relative to Nile red or Rhodamine B in 1 according to Eq. 1. 1,2 Φ 2Φ (1) Φ UC, A UC, I UC, and η UC represent the quantum yield, absorbance at λ ex, integrated photoluminescence spectral profile, and refractive index of the medium in the upconversion sample. The corresponding terms for the subscript std are for the reference quantum counter Nile red or Rhodamine B in liquid 1 at the identical corresponding excitation wavelength. The factor of 2 is included since upconversion requires the absorption of 2 photons to produce 1 whereas the reference actinometer s emission is directly proportional to the incident photons. Since the standard and the upconversion doped liquids are all in the same liquid 1, the refractive indices are the same. Therefore, under our experimental conditions, Eq. 1 simplifies to: Φ 2Φ (2) The reference chemicals, Nile red and Rhodanmine B, were soluble in liquid 1 below the mixing ratio of dye/1 = 1 mol%, as confirmed by the optical microscopy. The absolute fluorescence quantum yields were 0.75 and 0.06 for Nile red and Rhodamine B in liquid 1, respectively (dye/1 = 0.01 mol%). These quantum yield values are averaged values of at least three independent measurements. These data were obtained reproducibly for several different specimens with different mixing ratios. Supporting figures and tables Figure S1. Qualitative Jablonski diagram showing the sensitized triplet-triplet annihilation (TTA)-based upconversion emission, using 2 as the triplet photosensitizer and liquid 1 as the triplet acceptor (and the emitter). ISC: intersystem crossing, TTET: triplet-triplet energy transfer. S3

4 Figure S2. Photographs of liquid 1 under (a) visible and (b) UV (365 nm) light. Figure S3. A DSC thermogram of 1 in the cooling trace (10 C/min). The observed inflection is assignable to a glass transition. The glass transition temperature at 59 C was reproducibly observed upon repeating heating-cooling cycles for more than 3 times. S4

5 Figure S4. (a) Storage modulus (G'; black square) and loss modulus (G''; red circle) versus angular frequency of 1. (b) Complex viscosity (η*) versus angular frequency of 1 (η* = 0.99 Pa s). The observed larger loss modulus G compared to the storage modulus G indicates that the compound 1 is in the liquid state. The liquid 1 has a smaller viscosity than glycerol (1.2 Pa s) and comparable to other liquid aromatics. 3 Figure S5. (a) XRD and (b) SAXS profiles of liquid 1. In the XRD analysis, 1 exhibits a halo in the wide angle region corresponding to an average distance between the molten aliphatic chains of 4.4 Å (2θ = 19.9º). In the SAXS analysis, 1 exhibits a wide halo in the small angle region corresponding to the disordered anthracene core-to-core average distance of 21 Å. 3 S5

6 Figure S6. (a) Optical microscope image and (a ) polarized microscope image of the mixture of 1 and PtOEP (PtOEP/1 = 1 mol%). (b) Optical microscope image and (b ) polarized microscope image of the mixture consisting of 1 and 2 (2/1 = 1 mol%). Figure S7. (a) Luminescence decay observed for liquid 1 in CHCl 3 (0.1 mm, black line) and solvent-free state (blue line) (λ ex = 365 nm, λ em = 450 nm). The fluorescence lifetimes obtained by single exponential fittings were 6.53 ns and 7.66 ns for the solution and neat liquid, respectively. (b) Luminescence decay curves obtained for the delayed luminescence by TTA upconversion in air (blue line) and in vacuum (red line) from 2-doped liquid 1 (2/1 = 0.01 mol%; λ ex = 531 nm, λ UC = 450 nm). It is to note that the luminescence reported for related liquid compounds with different alkyl chain structures has been fitted with a biexponential decay. 3 In contrast, the data obtained for liquid 1 can be fitted with a single exponential function. Fitting of the result by using a biexponential function gave only negligible portion of the second component. This difference ensures high purity of the present liquid acceptors and also implies the importance of alkyl chain structures to photochemically isolate liquid chromophores. S6

7 511 nm Figure S8. Normalized absorption and emission (λ ex = 375 nm) spectra of the doped liquid 1 (2/1 = 0.01 mol%). The 2-doped liquid sample showed a Q-band at 511 nm, which is close to that of 2 dissolved in CHCl 3 (Figure 3a). The cast film of 2 showed a red-shifted Q-band at 518 nm, reflecting the formation of aggregates in the solid (Figure 3b). It was further supported by luminescence spectral measurement for the solid film 2 (λ ex = 520 nm), which gave phosphorescence at 718 nm with a shoulder peak at 827 nm (Figure 3b). The latter 827 nm peak can be assigned to the dimer emission. 4 These data support that 2 is molecularly dispersed in the acceptor liquid 1. Figure S9. (a) Photoluminescence spectra of the doped liquid (2/1 = 0.01 mol%) with different incident power density of 532 nm laser in vacuum. (b) Incident power density dependence of upconversion emission intensity at 433 nm of the doped liquid (2/1 = 0.01 mol%) in vacuum. The dashed lines are fitting results with slopes of 2.0 (blue) and 1.0 (red) in the low and high power density regimes, respectively. S7

8 Figure S10. Time-dependence of UC quantum yield observed for the aerated 2-doped liquid 1 (2/1 = 0.01 mol%; λ ex = 532 nm, excitation power, ca. 500 mwcm -2 ). Remarkably, there was no substantial loss in the quantum yield within 20 days. Even after keeping the sample in air for longer than 80 days, the reasonably high quantum yield of 15% was maintained. The observed drop of quantum yield to 15% is attributable to the oxidation of anthracene chromophores, 3 since degassing of the liquid sample under vacuum did not result the recovery of the quantum yield. These results demonstrate the excellent air-stability of the current fluid upconversion system, which would be explainable in terms of the air-sealing ability of clustering alkyl chains introduced to the chromopohores. Figure S11. Plots of temperature-dependent UC emission intensity at λ em = 433 nm (λ ex = 532 nm) of the doped liquid (2/1 = 0.01 mol%). S8

9 Table S1. Absolute quantum yields determined for 1 in CHCl 3 solution* and 2-doped liquid 1 at various mixing ratio (λ ex = 365 nm). 0 mol% Molar ratio (2/1) in CHCl 3 0 mol% mol% 0.01 mol% 0.1 mol% 1 mol% solution* Absolute QY (Φ A ) References: (1) Singh-Rachford, T. N.; Castellano, F. N. Coord. Chem. Rev. 2010, 254, (2) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991. (3) Babu, S. S.; Hollamby, M. J.; Aimi, J.; Ozawa, H.; Saeki, A.; Seki, S.; Kobayashi, K.; Hagiwara, K.; Yoshizawa, M.; Möhwald, H.; Nakanishi, T. Nat. Commun. 2013, 4, (4) (a) Bansal, A. K.; Holzer, W.; Penzkofer, A.; Tsuboi, T. Chem. Phys. 2006, 330, 118. (b) Mezyk, J.; Kalinowski, J.; Meinardi, F.; Tubino, R. Appl. Phys. Lett. 2005, 86. S9