Photo-Responsive Supramolecular Polymer Networks via Hydrogen Bond Assisted Molecular Tweezer/Guest Complexation

Transcription

1 Photo-Responsive Supramolecular Polymer Networks via Hydrogen Bond Assisted Molecular Tweezer/Guest Complexation Zongchun Gao, Yifei Han, Shuhan Chen, Zijian Li, Huijuan Tong, and Feng Wang*, Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, Anhui (P. R. China), Fax: (+86) ; Department of Chemistry and Materials Engineering, Hefei University, Hefei, Anhui (P. R. China). Supporting Information 1. Materials and Methods S2 2. Characterization of monomers 3 and 5 S4 3. Molecular tweezer/guest complexation between 1 and 4a S6 4. Characterization of supramolecular polymer networks 2/3 S9 5. Photo-responsiveness of supramolecular polymer networks 2/5 S11 6. Thermal behaviors of supramolecular polymer networks 2/3 S14 7. Synthetic route to monomers 2, 3, and 5 S Synthesis of monomer 10 Synthesis of monomer 2 S15 S Synthesis of compound 15 S Synthesis of PCLs 7, 8 and 9 S Synthesis of 3 and 5 S22 1

2 1. Materials and Methods Pentaerythritol, ε-aprolactone, tosyl chloride, sodium azide, sodium ascorbate, copper sulfate pentahydrate, paracetamol, 3-bromopropyne, phenol, p-anisidine and 4,5-dimethoxy-2-nitrobenzyl bromide were reagent grade and used as received. [Pt(tpy)Cl](BF 4 ), compounds 1, 4a, 11, 12, 13, and 14 were synthesized according to the previously reported procedures. [S1 S3] Other reagents and solvents were employed as purchased. 1 H NMR spectra were collected on a Varian Unity INOVA-300 or INOVA-400 spectrometer with TMS as the internal standard. 13 C NMR spectra were recorded on a Varian Unity INOVA-300 spectrometer at 75 MHz. Two-dimensional DOSY spectra were performed on a Varian Unity INOVA-400 MHz spectrometer. UV/Vis spectra were recorded on a UV-1800 Shimadzu spectrometer. Electrospray ionization mass spectra (ESI-MS) were obtained on a Bruker Esquire 3000 plus mass spectrometer (Bruker-Franzen Analytik GmbH Breman, Germany) equipped with an ESI interface and ion trap analyzer. Viscosity measurements were carried out with Ubbelohde semi-micro dilution viscometer (Shanghai Liangjing Glass Instrument Factory, 0.36 mm inner diameter) at 25 ºC in chloroform solution. Molecular weights and molecular weight distributions were determined by GPC/MALS using an SSI pump connected to a Wyatt DAWN HELEOS II light scattering instrument and Wyatt S18 Optilab T-rEX with DMF containing 0.02 M LiBr as the eluent at a flow rate of 1.0 ml/min. Fourier transform infrared (FTIR) spectra were obtained on a Nicolet 6700 FTIR spectrophotometer. The samples were mixed with KBr crystalline powders and pressed into tablets before characterization. Thermal transitions were determined by Perkin Elmer Pyris DSC under nitrogen atmosphere, with the heating and cooling rates of 5 K min -1. Titration Calorimetry (ITC) experiments were carried out with a Microcal VP-ITC apparatus at 298 K. Electron spin resonance (ESR) measurements were performed on a JEOL JES-FA200 apparatus, with the utilization of 2,2,6,6-tetra-methylpiperidine as the spin trap for 1 O 2. Density functional theory (DFT) calculations were carried out on the Gaussian 09 D.01 version software package. 2

3 During the theoretical calculations, all Pt atoms were described by Stuttgart effective core potential (SDD), whilst PBEPBE/3-21G basis set was selected to describe residual elements in all of the optimized complexes. 3

4 2. Characterization of monomers 3 and 5 (e) 7 (d) 8 (c) 9 (δ = 3.27 ppm) (b) triazole signal (δ = 7.63 ppm) 5 (a) 3 Figure S1. 1 H NMR spectra (300 MHz, CDCl 3, 298 K) of (a) 3; (b) 5; and the corresponding intermediates: (c) 9; (d) 8; (e) 7. Complete conversion of 9 to 3 and 5 can be validated by the vanishing of methylene 1 H NMR signals on 9 (δ = 3.27 ppm), together with the appearance of triazole resonances at 7.63 ppm. Compounds Mn / kda Đ t/min Figure S2. GPC traces (DMF as the eluent, polystyrene as the standards) of monomers 3, 5, and the corresponding intermediates 7 9. Insets: number-average molecular weight (M n ) and dispersity values of the synthetic polymers on the basis of GPC measurements. 4

5 2088 cm -1 Transmittance (%) Wavenumber (cm -1 ) Figure S3. IR spectra of monomer 3 and the corresponding precursor 9. Complete conversion of 9 to 3 is reflected by the disappearance of the azide stretching vibration band (2088 cm -1 ). 5

6 3. Molecular tweezer/guest complexation between 1 and 4a The binding stoichiometry between 1 and 4a was determined via 1 H NMR Job s plot (Figure S4 S5). (a) (b) (c) (d) (e) (f) (g) Figure S4. 1 H NMR spectra (300 MHz, CDCl 3, 298 K) of [1] and [4a] at different molar ratio, while the total concentration ([1] + [4a]) is kept constant at 4.00 mm: (a) 6 : 0; (b) 5 : 1; (c) 4 : 2; (d) 3 : 3; (e) 2 : 4; (f) 1 : 5; (g) 0 : δ(h a ) Molar Fraction Molar Fraction Figure S5. Job s plot curve by plotting the chemical shift of H a against the mole fraction of the guest. It proves 1 : 1 binding stoichiometry between 1 and 4a. 6

7 After determining 1 : 1 binding stoichiometry between 1 and 4a, 1 H NMR titration experiments were performed. In detail, the initial concentration of 1 was kept constant at 2.00 mm, while concentration of 4a was systematically varied. It leads to the gradual downfield chemical shifts for proton H 5 and upfield shifts for proton H 3 on 1 (Figure S6). Hence, treatment of the collected chemical shifts for protons on 1 vs the concentration of guest added (C A ), with a non-linear least-squares curve-fitting equation, affords the association constants. Specifically, for 1 : 1 host/guest complexation, the binding constants are calculated according to the following equation: 4 (Equation S1) Parameters δ 0 and δ are the chemical shifts for a selected host proton with and without the presence of the guest, respectively. [C 0 ] is the total concentration of the host, whilst [C A ] is the concentration of the guest. δ lim is the limiting value of chemical shifts for a selected host proton with the presence of excess guest. K a is the binding constant. In our study, by nonlinear curve-fitting of the collected 1 H NMR resonances of H 3 (according to Eq. S1), K a value for complex 1/4a is determined to be (5.89 ± 0.48) 10 3 M -1 (see Figure 1a in the main text). Figure S6. 1 H NMR titration spectra (300 MHz, CDCl 3, 298 K) of 1 at the concentration of 2.00 mm upon progressive addition of 4a. 7

8 Moreover, the exact role of intermolecular hydrogen bond for non-covalent complexation of 1/4a was evaluated via solvent-dependent 1 H NMR experiments (Figure S7). In particular, upon adding 5% methanol-d 4 into the chloroform-d solution of 4a, chemical shift changes can be hardly observed (Figure S7a b). In stark contrast, for 1/4a under the same conditions, the azobenzene protons H a on 4a move downfield (Δδ = 0.41 ppm, Figure S7c d). Such results demonstrate the impact of solvent polarity on molecular tweezer/guest complexation. Notably, the tendency for such chemical shift changes is contrary to that of 1/4a complexation process. Hence, it is apparent that intermolecular O H---N hydrogen bond plays a vital role for the sufficient binding strength between 1 and 4a. Figure S7. Partial 1 H NMR spectra (300 MHz, 298 K, 4.00 mm for each monomer) of (a) 4a in CDCl 3 /CD 3 OD (95 : 5, v/v), (b) 4a in CDCl 3, (c) 1 : 1 mixture of 1/4a in CDCl 3, (d) 1 : 1 mixture of 1/4a in CDCl 3 /CD 3 OD (95 : 5, v/v), (e) 1 in CDCl 3. 8

9 pecificviscosit4. Characterization of supramolecular polymer networks 2/3 Supramolecular polymer networks tend to form via A 2 /B 4 -type non-covalent complexation between 2 and telechelic homotetratopic monomer 3. To confirm the formation of supramolecular polymeric structures, concentration-dependent size variation of 2/3 (2 : 1 mixture) was examined by means of 2D diffusion-ordered NMR (DOSY) and viscosity measurements. Figure S8. DOSY NMR spectra (400 MHz, CDCl 3, 298 K) of complex 2/3 at different concentration of monomer 2: left, M; right: M. Upon increasing the concentration of 2 from 2 mm to 10 mm, the diffusion coefficient values drop from m 2 s -1 to m 2 s 1. Hence, it supports concentration-dependent size expansion of the supramolecular polymer networks SyConcentration / mm Figure S9. Specific viscosities of 3 ( )and 5 ( ) at different concentration (CHCl 3, 298 K). Under the same conditions, monomer 3 shows relatively higher viscosity than that of 5. It is primarily ascribed to the presence of hydroxyl group on 3, which is prone to form intermolecular O H---O hydrogen bonds. 9

10 Equation y = a + b*x Weight No Weighting Residual Sum of Squares Pearson's r Adj. R-Square Value Standard Error Intercept Slope E-4 Equation y = a + b*x Weight No Weightin Residual Sum of Squares Pearson's r Equation Weight Residual Sum of Squares y = a + b*x No Weighting Value Value Standard Err Standard Erro 0.1 Intercept It is widely known that alkynylplatinum(ii) terpyridine possesses excellent photosensitization capability. Considering that such organoplatinum(ii) species are inherently embedded in 2, we turned to examine singlet oxygen ( 1 O 2 ) generation capability for complex 2/3 (2 : 1 mixture), which is capable of forming supramolecular polymer networks at high monomer concentration (Figure S10) a b Adj. R-Squar Intercept Slope E-4 Intensity Absorbance ln(at/a0) Irradiation time / s Absorbance c Magnetic field / mt -ln(at/a0) Irradiation time / s Absorbance d Wavelength/nm -ln(at/a0) Pearson's r Adj. R-Square Slope E Irradiation time / s Wavelength/nm Wavelength / nm Figure S10. (a) EPR spectra (1.00 mm in CHCl 3 ) of complex 2/3 with the presence of TEMP (20.0 mm). The red line denotes the sample without irradiation, whilst the black line stands for the sample after visible light irradiation (460 nm, 12 W). Photo-excitation (460 nm, 12 W) of complex 2/3 and DMA (0.25 mm in chloroform) at the monomer concentration of: (b) mm, (c) mm, (d) mm. Accordingly, both EPR and UV-Vis experiments prove the generation of 1 O 2, which can be captured by TEMP and DMA in EPR and UV-Vis measurements, respectively. 10

11 5. Photo-responsiveness of supramolecular polymer networks 2/5 Stimuli-responsiveness of supramolecular polymer networks 2/3 was exploited, by regulating the fundamental molecular tweezer/guest complexation strength. Azobenzene compound is well-known for reversible cis-trans formation upon light irradiation. On this account, we firstly studied the cis-trans conversion of 4a (Figure S11), which is the basic building block in supramolecular polymer networks 2/3. As a comparison, photo-responsiveness was also studied for 4b. 4a 4b a before irradiation irradiation for 2 min 15 s in the dark b before irradiation irradiation for 2 min 2 min in dark 7 min in dark Absorbance Absorbance Wavelength/nm Wavelength/nm Figure S11. Photo-triggered trans-cis conversion of the azobenzene compounds: (a) 4a, and (b) 4b. Upon irradiation at 365 nm for 2 min, 4b shows the typical absorbance of cis-form, which is quite stable in the dark state. In sharp contrast, 4a shows the original absorbance of trans-form. According to the previous literatures, [S4] such phenomena should be ascribed to the presence of para-hydroxyl unit, which significantly speeds up the transition from photo-generated cis-form to photo-stationary trans-form. As an alternative method, a photo-cleavable nitrobenzyl dimethyl ether moiety is attached to the hydroxyl unit of azobenzene units. For the resulting compounds 5 6, photo-deprotection proceeds smoothly upon UV light irradiation (365 nm, 9 4 W), as reflected by the decrease of the benzylic 1 H NMR resonances on 5 (Figure S13) and 6 (Figure S12). 11

12 (e) (d) (c) H benzyl (b) (a) Figure S12. Partial 1 H NMR spectra (300 MHz, CDCl 3, 298 K, 4.00 mm) of (a-d) 6 after irradiation at 365 nm for (a) 0 min, (b) 15 min, (c) 35 min, (d) 65 min; (e) 4a. Upon light excitation, the 1 H NMR resonance for the benzylic proton (5.59 ppm) on 6 progressively decreases in intensity, and totally disappears after irradiation for 65 min. In the meantime, the newly formed 1 H NMR resonances coincide very well with those of guest 4a, indicating the smooth removal of the photo-cleavable group. (d) (c) (b) (a) Figure S13. Partial 1 H NMR spectra (300 MHz, 298 K, 5.00 mm) of (a-c) 5 after irradiation at 365 nm for (a) 0 min, (b) 40 min, (c) 120 min; (d) 3 in chloroform-d. Upon light excitation, the 1 H NMR resonance for the benzylic protons (5.58 ppm) progressively decreases in intensity, and totally disappears after irradiation for 120 min (Figure S13). In the meantime, the newly formed 1 H NMR resonances coincide very well with those of guest 3, indicating the smooth removal of the photo-cleavable group. 12

13 Furthermore, complex 1/6 is found to undergo photo-triggered transition from ''uncomplexed'' to ''complexed'' states (Figure S14). Specifically, due to the absence of intermolecular hydrogen bonds, guest 6 is unable to sandwich into the cavity of molecular tweezer 1. Upon UV light irradiation, 1 H NMR spectrum of 1/6 coincides very well with that of 1/4a. Similar behaviors are also observed for 2/5 (Figure S15). Figure S14. Partial 1 H NMR spectra (300 MHz, CDCl 3, 298 K, 4.00 mm) of (a) 1/6; (b) 1/6 after irradiation at 365 nm for 60 min; and (c) 1/4a. For complex 1/6, the transition from ''uncomplexed'' to ''complexed'' states can be directly reflected by the upfield shifts of H a, H d after light irradiation. Figure S15. Partial 1 H NMR spectra (300 MHz, 298 K, 5.00 mm for 2 in chloroform-d) of (a) 3; (b) 2/3 (2 : 1 mixture); (c) 2; (d) 2/5 (2 : 1 mixture); (e) 2/5 after irradiation at 365 nm for 200 min; and (f) 5. 13

14 6. Thermal behaviors of supramolecular polymer networks 2/3 (a) (b) (c) (d) Figure S16. DSC measurements of (a) 2 : 1 mixture of 2/3; (b) 5; (c) 2 : 1 mixture of 2/5 before irradiation at 365 nm; and (d) 2 : 1 mixture of 2/5 after irradiation at 365 nm. 14

15 7. Synthetic route to monomers 2, 3, and 5 Scheme S1. Synthetic route to monomer 2. Scheme S2. Synthetic route to monomers 3 and Synthesis of 10 Compound 11 (226 mg, 0.28 mmol) and K 2 CO 3 (233 mg, 1.69 mmol) were placed in a 50 ml round bottomed flask. Compound 12 (314 mg, 0.85 mmol) in CH 3 CN (25 ml) was added, and the resulting mixture was stirred overnight. The solvent was then evaporated under reduced pressure, and the residue was extracted with H 2 O/CH 2 Cl 2. 15

16 After the combined organic extracts were dried over anhydrous Na 2 SO 4 and evaporated with a rotary evaporator, the residue was purified by flash column chromatography (petroleum ether/ch 2 Cl 2, 2 : 1 v/v as the eluent) to afford compound 10 as a white solid (240 mg, 61.5%). 1 H NMR (300 MHz, CDCl 3 ) δ (ppm): 8.29 (s, 4H), 8.21 (d, J = 7.8 Hz, 4H), 7.87 (s, 4H), 7.71 (d, J = 8.7 Hz, 4H), 7.58 (d, J = 7.6 Hz, 4H), 7.48 (t, J = 7.7 Hz, 4H), 7.16 (d, J = 8.6 Hz, 4H), 7.08 (s, 2H), 5.21 (s, 4H), 4.01 (t, J = 6.4 Hz, 4H), 3.14 (s, 4H), (m, 4H), 1.43 (s, 4H), 1.21 (d, J = 9.3 Hz, 56H), 0.86 (t, J = 6.3 Hz, 6H). 13 C NMR (75 MHz, CDCl 3, 298 K) δ (ppm): , , , , , , , , , , , , , , , , 83.70, 69.08, 65.11, 31.94, 29.71, 29.67, 29.65, 29.44, 29.41, 29.38, 26.19, 22.71, ESI MS m/z: [M + H] +, Figure S17. 1 H NMR spectrum (300 MHz, CDCl 3, 298 K) of

17 Figure S C NMR spectrum (75 MHz, CDCl 3, 298 K) of 10. Figure S19. Electrospray ionization spectrum of Synthesis of 2 Compound 10 (207 mg, 0.15 mmol), [Pt(tpy)Cl](BF 4 ) (540 mg, 0.75 mmol), CuI 17

18 (50.0 mg, 0.25 mmol) and NEt 3 (2.5 ml) were dissolved in 50 ml of CH 2 Cl 2 and stirred at room temperature for 48 hours. The mixture was evaporated under reduced pressure, and the residue was purified by column chromatography (alumina, CH 3 OH/CH 2 Cl 2, 100 : 1 v/v as the eluent) to afford 4 as a yellow solid (420 mg, 68%). [S2] 1 H NMR (300 MHz, CD 2 Cl 2, 298 K) δ (ppm): 9.15 (d, J = 6.0 Hz, 8H), 8.65 (s, 8H), 8.58 (s, 8H), 8.40 (s, 4H), 8.08 (d, J = 7.6 Hz, 4H), 7.95 (s, 4H), 7.78 (d, J = 8.5 Hz, 4H), 7.59 (m, 12H), 7.47 (t, J = 7,6 Hz, 4H), 7.16 (d, J = 8.8 Hz, 4H), 7.07 (s, 2H), 7.03 (d, J = 9 Hz, 4H), 5.19 (s, 4H), 3.99 (t, J = 6.3 Hz, 4H), 1.58 (m, 36H), 1.47 (m, 72H), 1.16 (m, 64H), 0.84 (t, J = 6.9 Hz, 6H). 13 C NMR (75 MHz, CD 2 Cl 2, 298K) δ (ppm): , , , , , , , , , , , , , , , , , , , , , , , 98.90, 69.56, 65.43, 37.74, 36.72, 32.30, 30.63, 30.34, 30.08, 30.03, 29.74, 26.52, 23.07, ESI MS m/z: [M 4BF 4 ] 4+, Figure S20. 1 H NMR spectrum (300 MHz, CD 2 Cl 2, 298 K) of 2. 18

19 Figure S C NMR spectrum (75 MHz, CDCl 3, 298 K) of 2. Figure S22. Electrospray ionization spectrum of Synthesis of 15 4,5-Dimethoxy-2-nitrobenzyl bromide (276 mg, 1.00 mmol), 14 (200 mg, 0.80 mmol) and K 2 CO 3 (276 mg, 2.00 mmol) were mixed together in CH 3 CN (30 ml). 19

20 The resulting mixture was stirred overnight. The solvent was evaporated under reduced pressure, and the residue was extracted with H 2 O/CH 2 Cl 2. After the combined organic extracts were dried over anhydrous Na 2 SO 4 and evaporated with a rotary evaporator, the residue was purified by flash column chromatography (petroleum ether /CH 2 Cl 2, 2 : 1 v/v as the eluent) to afford 6 as a yellowish solid (325 mg, 92%). It was obtained as a yellow solid (300 mg, 85%). 1 H NMR (400 MHz, CDCl 3, 298 K) δ (ppm): 7.84 (d, J = 2.5 Hz, 2H), 7.81 (d, J = 2.5 Hz, 2H), 7.73 (s, 1H), 7.27 (s, 1H), 7.03 (dd, J = 12.7, 5.6 Hz, 4H), 5.52 (s, 2H), 4.70 (d, J = 2.4 Hz, 2H), 3.90 (d, J = 4.7 Hz, 6H), 2.49 (t, J = 2.4 Hz, 1H). 13 C NMR (75 MHz, CDCl 3, 298 K) δ (ppm): , , , , , , , , , , , , , 77.12, 74.97, 66.29, 55.48, 55.46, 55.04, ESI MS m/z: [M + H] +, Figure S23. 1 H NMR spectrum (300 MHz, CDCl 3, 298 K) of

21 Figure S C NMR spectrum (300 MHz, CDCl 3, 298 K) of 15. Figure S25. Electrospray ionization spectrum of Synthesis of PCLs 7, 8 and 9 To a previously flamed reaction tube equipped with a magnetic stirring bar, pentaerythritol (0.136 g, 1.00 mmol), Sn(Oct) 2 (0.040g, mmol), ε-caprolactone (9.20 g, 80.0 mmol), and dry toluene (15 ml) were added. After removal of 8 ml of toluene under reduced pressure, the tube was sealed under nitrogen gas, and placed in an oil bath thermostated at 100 o C. After stirring for 24 h, the resulting mixture was dissolved in THF and precipitated into an excess of cold methanol. After repeating the 21

22 precipitation and centrifugation procedures for 3 times, 7 was obtained as a white solid (7.01 g, yield: 75%). On this basis, 7 (5.45 g, 0.60 mmol), triethylamine (0.61 g, 6.00 mmol), trimethylamine hydrochloride (0.03 g, 0.36 mmol) were dissolved in CH 2 Cl 2 (50 ml). After cooling to 0 C, tosyl chloride (1.14 g, 6.0 mmol) in CH 2 Cl 2 (20 ml) was added dropwise over 1 h. After stirring at room temperature overnight, the resulting mixture was dissolved in THF and precipitated into an excess of diethyl ether. After repeating the precipitation and centrifugation procedures for 3 times, 8 was obtained as a white solid (5.10 g, yield: 85%). Subsequently, 8 (1.70 g, 0.17 mmol), DMF (20 ml), and NaN 3 (0.10 g, 1.70 mmol) were added to a 50 ml round-bottom flask. The reaction mixture was heated at 45 ºC for 24 h. After removing solvents at reduced pressure, the residue was dissolved in THF, and passed through a neutral alumina column. After precipitation (Et 2 O) and centrifugation for several times, PCL-N 3 (9) was obtained as a white solid (1.05 g, yield: 62%). 1 H NMR and GPC spectra of 7, 8 and 9 are shown in Figure S1 S Synthesis of 3 and 5 Compounds 9 (450 mg, 0.50 mmol) and 14 (75.6 mg, 0.30 mmol) were dissolved in 50 ml of DMF. An aqueous solution (15 ml) of monosodium L-ascorbate (158 mg, 0.80 mmol) and CuSO 4 5H 2 O (100 mg, 0.40 mmol) was then added. The resulting mixture was heated at 60 C and stirred for 72 hours. The solvent was removed with a rotary evaporator, and the residue was extracted with H 2 O/CH 2 Cl 2. The combined organic extracts were dried over anhydrous Na 2 SO 4 and removed with a rotary evaporator. The residue was passed through a neutral alumina column. After 22

23 precipitation (Et 2 O) and centrifugation for several times, 3 was obtained as a yellowish solid (240 g, yield: 51 %). Similar procedure was adopted for the synthesis of 5, with the utilization of 9 and 15 as the reactants. 1 H NMR and GPC spectra of 3 and 5 are shown in Figure S1 S2. 23

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