Nanocage-confined synthesis of fluorescent polycyclic aromatic hydrocarbons in zeolite

Transcription

1 Nanocage-confined synthesis of fluorescent polycyclic aromatic hydrocarbons in zeolite Seung Hyeon Ko, *, Taekyoung Lee,, Hongjun Park,, Doo-Sik Ahn, Kyoungsoo Kim, Yonghyun Kwon,, Sung June Cho & Ryong Ryoo *,, Center for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea. Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea. Clean Energy Technology Laboratory and Department of Chemical Engineering, Chonnam National University, Gwangju 61186, Korea. S1

2 Experimental Details Preparation of zeolite A. Zeolite A was synthesized according to the previous literature procedures. 1 For X-ray crystallography, zeolite A with large single-crystal morphology was synthesized. 2 Na + ions in zeolite A (NaA) were fully ion exchanged by Ca 2+ ions (CaA) using aqueous solutions of calcium chloride hexahydrate. Synthesis of PAHs using CaA. CaA was placed in a tubular quartz reactor which was equipped with a fritted disc. Temperature of the reactor was raised to the designated value under N 2 flow. The reaction temperatures were chosen for systematic studies: the lowest temperature which could produce the products using CaA (400 C) and the highest temperature which did not generate any external deposition (520 C). When the temperature was stabilized, the N 2 flow was switched to acetylene/n 2 gas mixture (16% v/v in N 2 for 400 C and 5% v/v for 520 C) with a total flow rate of 60 ml min -1. The water vapor saturated at 30 C was added to the flow at the same time. The resultant product was washed three times by aqueous solutions of HF and HCl and then dried under vacuum at room temperature. Characterization. The PAH content was determined by thermogravimetric analysis using a TGA Q50 (TA Instruments). UV/Vis absorption and fluorescence spectra of the PAHs in NMP were recorded on UV-2600 (Shimadzu) and LS55 (PerkinElmer) spectrophotometer, respectively. Matrix assisted laser desorption/ionization reflectron time-of-flight technique (MALDI-ReTOF, UltrafleXtreme, Bruker Daltonics) was used to analyze molecular weight of the PAHs. For the mass analysis, the PAHs were dissolved in 1-chloronaphthalene. Elemental analysis of the products was performed by a Flash 2000 elemental analyzer (Thermo Scientific). 13 C solid-state nuclear magnetic resonance (NMR) spectra were acquired using Bruker AVANCE III HD 400WB at room temperature. The spectrometer was equipped with a 4 mm magic angle spinning (MAS) probe, and the MAS speed was 13 khz. 13 C MAS NMR measurement was carried out with the π/2 pulse width of 3.8 µs and a relaxation delay of 5 s. The frequency was MHz. Resonance positions were referenced with respect to the CH 2 resonance of adamantane. 1 H and 13 C solution-state NMR measurements were carried out using Agilent DD2 400 MHz spectrometer at room temperature. The samples used for NMR experiments were dissolved in CD 2 Cl 2. Chemical shifts were quoted in parts per million (ppm) and referenced to the residual solvent signals (5.32 ppm for 1 H and ppm for 13 C). The frequencies for 1 H and 13 C were and MHz, respectively. Separation of PAHs into distinctly emitting groups. The synthesized PAHs were separated into distinctly emitting groups by silica gel column chromatography. As the eluent, hexane was used and slowly switched to hexane/dichloromethane (3:1) and further dichloromethane. The blue-emittinggroups were extracted by hexane and the G group was extracted by hexane/dichloromethane (3:1). Dichloromethane was used for extraction of the O group. Preparation of LED devices. The LED devices were made by coating the light unit (LED Engin) comprised of a 365 nm excitation light emitting chip with each emitter dissolved in NMP. The coating of emitter solution was dried at room temperature. The power supply was connected to display emission. The emission of our device (16 mm 2 ) was operated at 4.5 V. S2

3 Crystallographic data collection. Single crystal of LTA zeolite containing PAHs (about 35 µm in diameters) was dehydrated under high-purity N 2 gas flow at 400 C for 2 h, followed by drying under vacuum at 150 C for 4 h, to fully exclude moisture. To prevent moisture absorption during the processes, the crystal was coated with a layer of Paratone oil, which was pre-dehydrated for 24h, in a glove box. The diffraction data of a single crystal were measured at 100 K using synchrotron radiation with ADSC Quantum-210 detector at 2D SMC with a silicon (111) double crystal monochromater (DCM) at the Pohang Accelerator Laboratory, Korea. ADSC Q210 ADX software was used for data collection (detector distance = 63 mm, omega scan; ω = 1, and exposure time = 2 s per frame), and HKL3000sm was used for the cell refinement, reduction, and absorption correction. Derivation of electron density map for carbon. Single crystal XRD data collected from LTA containing PAHs were analyzed by means of full-matrix least squares calculation, based on F 2 values with JANA2006. The detailed procedure was the same as described elsewhere. 3 Briefly, we obtained the electron-density map (i.e., zeolite framework + PAHs) by the dual-space method with a chargeflipping algorithm. Based on the density map, a space group of Pm-3m was determined. Zeolite framework structure was refined according to this space group. In the refinement process, zeolite framework was refined using high-angle portion of XRD data above sinθ/λ = 0.25 (corresponding to d 0.2 nm). It excluded all effects of intra-pore PAH deposition on XRD in the low-angle region. 4 The refined zeolite framework was set as an initial value for further refinement. Subsequently, the carbon atoms in zeolite pores were found using the difference Fourier method over the entire set of XRD data. In this process, all carbon atoms were assumed to have the same atomic displacement parameter. This assumption was taken to refine carbon atoms without restraints for atomic bonding and geometry. Then, using the carbon atoms and zeolite framework obtained above as initial values, the entire structure was further refined. The refinement was continued with the assumption of same atomic displacement parameters for all carbons until convergence was confirmed. The details of the refinement data were provided in SI Table S1. After removing all carbon atoms in zeolite pores, we visualized an electron-density map corresponding to PAHs by using the difference Fourier method. This electron-density map was equivalent to the difference between the total electron density and finally refined zeolite framework. DFT calculations. All DFT calculations were implemented with the Gaussian09. 5 Geometrical optimizations for minimum and transition states of isolated molecules were preliminarily searched with B3LYP/6-31G(d) level of theory and all the results were confirmed by the normal mode analysis and re-optimized at higher level (B3LYP/ G(d)). Zero-point vibrational energy was corrected as well. S3

4 Figure S1. FT-IR spectra of the products synthesized at (a) 400 C and (b) 520 C. For the product synthesized at 400 C, the spectrum displays the presence of sp 3 C-H (2920 cm -1 ) as well as sp 2 C-H (3010 cm -1 ) and sp 2 C=C (1600 cm -1 ). In comparison, the spectrum of the product synthesized at 520 C shows the presence of sp 2 C-H (3010 cm -1 ) and sp 2 C=C (1580 cm -1 ). Figure S2. Solid 13 C MAS NMR spectra of the products synthesized at 400 C (black) and 520 C (red). Asterisks indicate spinning side bands at 13 khz. 13 C NMR spectrum of the product synthesized at 520 C exhibited only a peak covering from 120 to 140 ppm, corresponding to sp 2 -carbon. In comparison, the product synthesized at 400 C showed a small peak of sp 3 -carbon (19.4 ppm) in 13 C NMR spectrum as well, indicating that a relatively small amount of sp 3 -carbons existed. S4

5 Figure S3. Mass spectrum of the product synthesized at 520 C, which shows preferential formation of the molecules centering at mass-to-charge ratios, m/z=300 (C 24 H 12 ), 374 (C 30 H 14 ), 398 (C 32 H 14 ) and 422 (C 34 H 14 ). As examples, possible PAH candidates are suggested for each m/z. S5

6 Figure S4. The expanded mass spectra of the products obtained at 400 C and 520 C showing a series of peaks at regular intervals of 24 amu and additional peaks of 14 amu larger than them. S6

7 Figure S5. A specific mechanism called hydrogen abstraction-acetylene addition (HACA). It implies consecutive reactions of hydrogen abstraction from the reacting aromatic hydrocarbon followed by acetylene addition to the radical site. Figure S6. The confined Ca 2+ -catalyzed condition induces the addition of an acetylene molecule first, followed by hydrogen abstraction, which is the reverse order of the HACA mechanism. S7

8 Figure S7. Effects of molecular geometries on relative energy and dipole moment of PAHs. The relative energies and dipole moments of several PAH molecules corresponding to m/z=398, which have different molecular geometries, were calculated. a, ovalene and curved mixed-ring species. b, hydrogenated ovalenes (m/z=400) with different positions of hydrogens. c, an energy level diagram for ovalene, curved PAHs, hydrogenated PAHs, and ovalenyl radical (m/z=397).; For hydrogenated species, the equation of [E(Hydrogenated)-E(H 2 )] was applied whereas the energy for ovalenyl radical was calculated using the equation of [E(radical)+E(H)]. S8

9 Figure S8. Possible candidate molecules that can reside inside α-cage of LTA. a, Maximum distance of molecular dimension for various molecules as a function of number of carbon inside the molecule. b, Molecular topology of LTA which consists of three different cages including cubes, truncated octahedra and truncated cuboctahedra. In the present work, truncated cuboctahedra (α-cage) has been used as a nanoreactor for polyarene synthesis. In the figure, (a) is unit cell length and (b) denotes maximum distance inside α-cage. Considering the α cage dimensions, it is likely that ovalene is the limit as a planar aromatic hydrocarbon molecule that can grow inside the α-cage. In the case that any larger PAH molecules are synthesized inside the α-cage, they should grow in curved shapes rather than planar ones. Figure S9. Calculated molecular dimensions of coronene and ovalene. Large spheres represent carbon atoms while small spheres are hydrogen atoms. S9

10 Figure S10. Examples of PAH growth based on acetylene addition-hydrogen abstraction. As a result, the mass spectrum displayed 24 mass interval between the products: 24 ( mass) = [addition of an acetylene molecule (mass = 26)] [loss of two hydrogen atoms (mass = 2)]. The mass spectrum of the PAHs synthesized at 520 C displays preferential formation of the molecules centering at mass numbers of 300, 374, 398 and 422 by excluding the peaks of methylated species (+14 series). S10

11 Figure S11. 1 H and 13 C solution-state NMR spectra of coronene (a & b) and the group B (c & d). Asterisks represent peaks from the solvents (Figure S14). S11

12 Figure S12. 1 H and 13 C solution-state NMR spectra of ovalene (a & b) and the group G (c & d). The NMR spectra of ovalene were produced by using a public program available online ( Asterisks represent peaks from the solvents (Figure S14). Figure S13. 1 H (a) and 13 C (b) solution-state NMR spectra of the group V. Regarding the Group V analysis, it was difficult to assign the mass spectrum, probably due to low ionization efficiency of small molecules and the existence of several molecular species in a mixture. Without knowing the molecular weights accurately, it was difficult to assign the NMR spectra properly. Asterisks represent peaks from the solvents (Figure S14). S12

13 Figure S14. 1 H and 13 C solution-state NMR spectra of CD 2 Cl 2 (a & b) and hexane (c & d). CD 2 Cl 2 is a solvent of NMR measurement and hexane is an extracting solvent of column chromatography. S13

14 Table S1. Data collection and refinement statistics for X-ray diffraction analysis S14

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