SUPPLEMENTARY INFORMATION

Transcription

1 Fast and long-range triplet exciton diffusion in metal organic frameworks for photon upconversion at ultralow excitation power Prasenjit Mahato, 1 Angelo Monguzzi, 2 Nobuhiro Yanai, 1,3* Teppei Yamada, 1,3 and Nobuo Kimizuka 1* 1 Deptartment of Chemistry and Biochemistry, Graduate School of Engineering, Center for Molecular Systems (CMS), Kyushu University, Fukuoka , Japan. 2 Dipartimento di Scienza dei Materiali, Università degli Studi Milano-Bicocca, via R. Cozzi 55, Milano, Italy. 3 PRESTO, JST, Honcho 4-1-8, Kawaguchi, Saitama , Japan. * Correspondence and requests for materials should be addressed to N.Y. (yanai@mail.cstm.kyushu-u.ac.jp) or to N.K. (n-kimi@mail.cstm.kyushu-u.ac.jp). NATURE MATERIALS 1

2 Supplementary Figure 1. X-ray power diffraction (XRPD) patterns (black) of MOF (a) 1, (b) 2 and (c) 3 with corresponding simulated patterns made from their crystal structures (blue). The phase purity of the MOFs was confirmed by the good agreement between the experimental and simulated patterns. Emission (arb. units) 1.0 ADBA MOF 1 MOF 2 MOF Wavelength(nm) Supplementary Figure 2. Photoluminescence spectra of the benzene solution of ligand adba (10 M) and benzene dispersions of MOF 1, 2 and 3 (0.2 wt%) (λex = 375 nm). 2 NATURE MATERIALS

3 SUPPLEMENTARY INFORMATION PL intensity (arb. units) = 4.1 ns Time (ns) Supplementary Figure 3. Photoluminescence decays at 435 nm of the benzene solution of ligand adba (black; 10 M) and the benzene dispersions (0.2 wt%) of MOF 1 (blue), 2 (red), and 3 (green) under pulsed excitation at 365 nm. The adba solution followed the single exponential behaviour with a lifetime of = 4.1 ns (purple line). In contrast, the MOF dispersions showed the multi-exponential behaviours typical of solid crystalline materials. NATURE MATERIALS 3

4 Supplementary Figure 4. (a) Phosphorescence spectrum of PtOEP in deaerated benzene (5 M, λex = 532 nm). Photoluminescence decays at 645 nm of (b) the benzene solution of PtOEP and of the benzene solution of PtOEP in presence of MOF (c) 1, (d) 2, and (e) 3 under pulsed excitation at 532 nm. In solution systems, the Dexter transfer rate is determined by the overall diffusivity of donor and acceptor. In our case, all MOF particles are significantly larger than the donor PtOEP (Supplementary Fig. 5), and thus the total diffusivity is determined mainly by the donor. Given a constant diffusion constant of donor PtOEP in benzene, the energy transfer yield would be determined by i) the acceptor crystal concentration, ii) the surface-to-volume ratio of the MOF crystals, and iii) the orientation of acceptor molecules on the MOF surfaces. It is difficult to compare quantitatively the TTET efficiency between different MOFs due to the last point, since the Dexter energy transfer is strictly dependent on the effective molecular orbital overlap between donor and acceptor. 4 NATURE MATERIALS

5 SUPPLEMENTARY INFORMATION Supplementary Figure 5. Scanning electron microscopy (SEM) images of MOF (a) 1, (b) 2, and (c) 3. a b c Wavelength (nm) Wavelength (nm) Wavelength (nm) Supplementary Figure 6. Photoluminescence spectra of benzene dispersions of MOF (a) 1, (b) 2, and (c) 3 after incubation of MOF 1-3 particles (3 mg/ml) in benzene solution of PtOEP (500 M) for 12 hours, filtration, and re-dispersion in deaerated benzene (λex = 532 nm, incident laser power density = 300 mw cm -2 ). If the donor PtOEP is introduced into the MOF pores during the incubation, the obtained re-dispersed samples should show the phosphorescence and/or upconverted emission. However, all the dispersions did not show any PtOEP phosphorescence at 645 nm nor upconverted emission at 440 nm. These results undoubtedly confirm that the donor PtOEP is not included in the pores of the acceptor MOFs. This is reasonable, since the molecular size of PtOEP (1.5 nm 1.5 nm 0.66 nm) is much larger than the pore sizes of the employed MOFs; MOF 2 has the largest pore size of nm among the three MOFs. Therefore, it would be difficult for PtOEP to be incorporated in the pores. This is further supported by the fact that MOF 2 having the largest pore size gave the lower donor-to-acceptor energy transfer efficiency than MOF 3 (Supplementary Tables 1-3). NATURE MATERIALS 5

6 Supplementary Figure 7. TTA-UC emission intensity (blue, Iuc) and residual donor phosphorescence intensity (red, Iph) for a deaerated benzene dispersion of PtOEP and MOF 2 as a function of the excitation intensity (λex = 532 nm). By further increasing the excitation power well above the threshold, we found that the UC emission intensity follows a sub-linear behaviour with respect to the excitation power density (Fig. 3d). It suggests the appearance of some additional channels which compete with the TTA. To enlighten this point, we measured the excitation power dependence of residual donor phosphorescence and compared it with the UC emission. As the excitation intensity increased, the excitation power dependence of donor phosphorescence changed from linear to sub-linear, indicating that the additional deactivation channel competitive to TTET towards MOFs at higher excitation intensity is ascribed to donors. This channel is expected as the homo-molecular annihilation between donor triplets (TTD). We can observe this effect only if the annihilation rate kttd is higher than other processes (kttd > kd + ket), where kd is the donor spontaneous decay rate and ket the TTET rate. At an excitation power named ITTD, transitions from linear to sublinear response were observed for both of UC emission and phosphorescence. Since bi-molecular annihilation is a diffusion controlled process, we can write as, (S1) where DD is the diffusion constant of donor, ad is the annihilation radius between donor triplets (1 nm in good approximation), CD is the donor triplet concentration, is the absorption coefficient at the excitation wavelength, and Iexc is the excitation intensity. By 6 NATURE MATERIALS

7 SUPPLEMENTARY INFORMATION defining ITTD as the intensity for the linear to sub-linear transition when kttd = kd+ket and by considering that, (S2) for the samples described in the main text we can predict the ITTD values as 38, 31, and 10 mw cm 2 for MOF 1, 2, and 3. These values are in good agreement with the experimental data, confirming our hypothesis. However, it should be pointed out that in our case ITTD is well above the solar irradiance (1.6 mw cm 2 at 532±5 nm) and the MOFs Ith, so it does not affect the performance of the MOFs as low-power upconverters. NATURE MATERIALS 7

8 a b 1.0 c Excitation Excitation power power Wavelength (nm) d UC emission intensity (arb. units) Wavelength (nm) Wavelength (nm) Supplementary Figure 8. Photoluminescence spectra of MOF 1 dispersed in deaerated benzene solution of PtOEP with different incident power density of 532 nm laser in (a) 1st (b) 2nd, and (c) 3rd attempts. (d) TTA-UC emission intensity for the deaerated benzene dispersion of MOF 1 with PtOEP as a function of the excitation intensity (λex = 532 nm) in 1st (black), 2nd (blue), and 3rd (red) attempts. The linear fits with slopes 2 and 1 in the lower and higher excitation power regimes are shown. Intersections between the two lines provide the threshold excitation intensity (Ith) Excitation power density(mw cm -2 ) 0.5 Excitation power 8 NATURE MATERIALS

9 SUPPLEMENTARY INFORMATION a b c uc = 376 s uc = 358 s PL Intensity (arb. unit) Time( s) d e 10 f 0 = 75 s = 80.3 s = 79.8 s uc = 384 s Supplementary Figure 9. Photoluminescence decays at 435 nm of the benzene dispersions of PtOEP and MOF 1 under pulsed excitation at 532 nm in (a) 1st (b) 2nd, and (c) 3rd attempts. Single exponential fittings of the tail parts (red lines) provide to estimate the triplet state lifetime ( T = 2 UC) in each case (Supplementary Table 1). Photoluminescence decays at 645 nm of the benzene solutions of PtOEP in the presence of dispersed MOF 1 under pulsed excitation at 532 nm in (d) 1st (e) 2nd, and (f) 3rd attempts. NATURE MATERIALS 9

10 Supplementary Figure 10. Photoluminescence spectra of MOF 2 dispersed in deaerated benzene solution of PtOEP with different incident power density of 532 nm laser in (a) 1st (b) 2nd, and (c) 3rd attempts. (d) TTA-UC emission intensity for the deaerated benzene dispersion of MOF 2 with PtOEP as a function of the excitation intensity (λex = 532 nm) in 1st (black), 2nd (blue), and 3rd (red) attempts. The linear fits with slopes 2 and 1 in the lower and higher excitation power regimes are shown. Intersections between the two lines provide the threshold excitation intensity (Ith). 10 NATURE MATERIALS

11 SUPPLEMENTARY INFORMATION a b c uc = 341 s uc = 490 s uc = 296 s d e f 78 s 80.7 s 79 s Time( s) Supplementary Figure 11. Photoluminescence decays at 435 nm of the benzene dispersions of PtOEP and MOF 2 under pulsed excitation at 532 nm in (a) 1st (b) 2nd, and (c) 3rd attempts. Single exponential fittings of the tail parts (red lines) provide to estimate the triplet state lifetime ( T = 2 UC) in each case (Supplementary Table 2). Photoluminescence decays at 645 nm of the benzene solutions of PtOEP in the presence of dispersed MOF 2 under pulsed excitation at 532 nm in (d) 1st (e) 2nd, and (f) 3rd attempts. NATURE MATERIALS 11

12 Supplementary Figure 12. Photoluminescence spectra of MOF 3 dispersed in deaerated benzene solution of PtOEP with different incident power density of 532 nm laser in (a) 1st (b) 2nd, and (c) 3rd attempts. (d) TTA-UC emission intensity for the deaerated benzene dispersion of MOF 3 with PtOEP as a function of the excitation intensity (λex = 532 nm) in 1st (black), 2nd (blue), and 3rd (red) attempts. The linear fits with slopes 2 and 1 in the lower and higher excitation power regimes are shown. Intersections between the two lines provide the threshold excitation intensity (Ith). 12 NATURE MATERIALS

13 SUPPLEMENTARY INFORMATION a b c uc = 510 s uc = 502 s Time( s) d e f 34.6 s 44 s 45.6 s uc = 538 s Supplementary Figure 13. Photoluminescence decays at 435 nm of the benzene dispersions of PtOEP and MOF 3 under pulsed excitation at 532 nm in (a) 1st (b) 2nd, and (c) 3rd attempts. Single exponential fittings of the tail parts (red lines) provide to estimate the triplet state lifetime ( T = 2 UC) in each case (Supplementary Table 3). Photoluminescence decays at 645 nm of the benzene solutions of PtOEP in the presence of dispersed MOF 3 under pulsed excitation at 532 nm in (d) 1st (e) 2nd, and (f) 3rd attempts. Supplementary Figure 14. XRPD patterns of the MOF 3 nanocrystals (black) and the simulation results from the crystal structure of MOF 3 (blue). NATURE MATERIALS 13

14 0.10 Absorbance Wavelength (nm) Supplementary Figure 15. Absorption spectrum of the PdMesoIX-modified MOF 3 nanocrystals in PMMA. Supplementary Figure 16. Photoluminescence decays at 650 nm of (a) PdMesoIX dispersed in PMMA and (b) the PdMesoIX-modified MOF 3 nanocrystals in PMMA. The TTET efficiency ET (0.61) was obtained by the equation, ET = 1 / 0, where 0 and were the donor (PdMesoIX) phosphorescence lifetime without and with acceptor MOF, respectively. (c) Photoluminescence decay at 435 nm of the PdMesoIX-modified MOF 3 nanocrystals in PMMA under pulsed excitation at 532 nm. Single exponential fitting of the tail part (red line) provides the acceptor triplet lifetime ( T = 2 UC) of 4.0 ms. 14 NATURE MATERIALS

15 SUPPLEMENTARY INFORMATION Supplementary Figure 17. Absorption spectra of deaerated benzene solutions of PtOEP containing MOF (a) 1, (b) 2, and (c) 3 measured after leaving the dispersions for longer than 12 h to let the particles sediment to the bottom of the cells. NATURE MATERIALS 15

16 Supplementary Table 1. Absorption coefficient, donor-to-acceptor TTET efficiency ΦET, acceptor triplet lifetime T, threshold excitation intensity for TTA-UC Ith, triplet exciton diffusion constant DT, and diffusion length LT for the deaerated benzene dispersions of PtOEP and MOF 1 in the three attempts. Averaged DT and LT values are also shown. Attempt / cm 1 ΦET T / ms Ith / mw cm 2 DT / cm 2 s 1 LT / m 1st nd rd average Supplementary Table 2. Absorption coefficient, donor-to-acceptor TTET efficiency ΦET, acceptor triplet lifetime T, threshold excitation intensity for TTA-UC Ith, triplet exciton diffusion constant DT, and diffusion length LT for the deaerated benzene dispersions of PtOEP and MOF 2 in the three attempts. Averaged DT and LT values are also shown. Attempt / cm 1 ΦET T / ms Ith / mw cm 2 DT / cm 2 s 1 LT / m 1st nd rd average Supplementary Table 3. Absorption coefficient, donor-to-acceptor TTET efficiency ΦET, acceptor triplet lifetime T, threshold excitation intensity for TTA-UC Ith, triplet exciton diffusion constant DT, and diffusion length LT for the deaerated benzene dispersions of PtOEP and MOF 3 in the three attempts. Averaged DT and LT values are also shown. Attempt / cm 1 ΦET T / ms Ith / mw cm 2 DT / cm 2 s 1 LT / m 1st nd rd average NATURE MATERIALS