Supporting Information

Alkylation of Spiropyran Moiety Provides Reversible Photo-control over Nanostructured Soft Materials

Wye-Khay Fong1, Nino Malic2, Richard A. Evans2, Adrian Hawley3, Ben J Boyd1*, Tracey L Hanley4*

1Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville Campus), 381 Royal Parade, Parkville, Victoria 3052, Australia, 2CSIRO Materials Science and Engineering, Clayton, South Victoria 3169, Australia, 3SAXS/WAXS beamline, Australian Synchrotron, Clayton, Victoria, Australia, 4Australian Nuclear Science and Technology Organisation, Locked Bag 2001 Kirrawee DC NSW 2232, Australia.

*Email addresses for corresponding authors: ;

Synthesis of spiropyran laurate (SPL) derivative: 2-(3’,3’-Dimethyl-6-nitro-3’H-spiro[chromen-2,2’-indol]-1’-yl)-ethanol 1 (0.50 g, 1.42 mmol) was dissolved in dry dichloromethane (10 mL) together with triethylamine (0.39 mL, 2.84 mmol), under nitrogen. Lauroyl chloride (0.33 mL, 1.42 mmol) was then added via syringe at room temperature. After stirring for 10 min the reaction mixture was passed through a plug of silica gel, the solvent evaporated in vacuo and the residue purified by column chromatography (SiO2, EtOAc/hexanes, 1:3). 1H NMR (400 MHz, d6-acetone) d 8.15 (d, J = 2.8 Hz, 1H), 8.05 (dd, J = 8.9, 2.8 Hz, 1H), 7.21 (d, J = 10.4 Hz, 1H), 7.19-7.13 (m, 2H), 6.85 (m, 2H), 6.76 (d, J = 7.8 Hz, 1H), 6.09 (d, J = 10.4 Hz, 1H), 4.25 (m, 2H), 3.56 (m, 1H), 3.46 (m, 1H), 2.24 (td, J = 7.5, 2.1 Hz, 2H), 1.53 (m br, 2H), 1.27 (m, 21H), 1.18 (s, 3H), 0.88 (t br, 3H) ppm.

Note: Lauroyl chloride was purchased from Aldrich and used as supplied.

UV spectral characterisation of SPL: UV−visible absorption spectra were measured on a Cary-50 spectrometer from 200−800 nm at a scan rate of 600 nm s−1 and kinetic measurements at 540 nm. The spectrometer was fitted with a Peltier temperature controlled cell. Solutions for UV−visible measurements were made at concentrations of 1 mg/mL in methanol and hexane.

SI Figure 1 – time dependence of the absorbance at 540 nm of a solution (1.87 × 10-3M, MeOH, 298 K) of SPL in the dark after 10 min of irradiation by UV (dashed) and white (solid) light. This allowed for the determination of k1obs (spiro à mero) and k2obs (mero à spiro), presented in SI Table 1, by fitting the plots above, with the equations 1 & 2 below.

This allowed for the determination of k1obs and k2obs (see SI Table 1) by fitting the plots above, with the equations 1 and 2:

1.  y = y0 – ae-k1obs x

2.  y = y0 + ae-k2obs x

SI Table 1. Observed rate constants for isomerization of SPL in different solvents at 1 mg/mL. The value of k1obs for SPL in hexane and phytantriol could not be determined due to the polarity of the solvent stabilizing the closed spiropyran form 2, 3.

Solvent / k1obs (after white light) / k2obs (after UV)
methanol / 4.5 × 10-4 s-1 / 4.0 × 10-4 s-1
hexane / n/a / 6.2 × 10-2 s-1
phytantriol-water liquid crystal / n/a / 1.1 × 10-3 s-1

Photochromic-liquid crystalline phases: Materials – Phytantriol (3,7,11,15-tetramethylhexadecane-1,2,3-triol) was a gift from DSM (Singapore) with nominal purity of >96.6%, spiropyran (SP) (1′,3′-Dihydro-1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-(2H)-indole]) was purchased from Sigma-Aldrich and Oxford Blue (spirooxazine (SOX)) was purchased from James Robinson. Phosphate buffered saline (PBS) salts, di-sodium hydrogen orthophosphate, anhydrous and sodium chloride were purchased from Univar, APS Ajax Finechem (Auburn, NSW, Australia), and potassium dihydrogen orthophosphate was purchased from BDH AnalaR, Merck Pty. Ltd (Kilsyth, VIC, Australia). All chemicals were used as received without further purification. Milli-Q grade water (0.05 μS cm-1 at 25°C) purified through a Millipore system (Sydney, Australia) was used for the preparation of all samples. The photochromics, SP, SPL and SOX were pre-dissolved in phytantriol. For bulk systems, PBS was added to the lipid phase in a ratio of 1:1 (w:w) to ensure excess water conditions 4-6.

SAXS – SAXS experiments were collected on the SAXS instrument at the Australian Synchrotron (http://www.synchrotron.org.au/index.php/aussyncbeamlines/saxswaxs/saxs-specifications). Samples were enclosed in a custom made HDPE/mylar/kapton cylindrical sample holder; diameter 6 mm, thickness 0.5 mm. An X-ray beam with a wavelength of 0.83 Ǻ (15 keV) was selected. The 2D SAXS patterns were collected using a Pilatus 200k detector (active area 169 × 33 mm2 with a pixel size of 172 μm) which was located 956 mm from the sample position. 2D SAXS patterns were collected for 10 ms every 2 s over repeated 60 seconds of UV exposure. The computer software SAXS15ID and Fit2D were used to acquire and reduce 2D patterns to a one-dimensional scattering function I(q). This geometry enables a study of the interplanar distance (d-spacing), d, between two reflecting planes in the range of 350 to 5 Å. The d-spacing is derived from Bragg’s law (λ= 2d sin θ; where λ is the wavelength of the incident radiation, and 2θ is the scattering angle) and is inversely related to the scattering vector, q (q = 4π sin θ/λ). The q is, in turn, related to the position of the scattered X-ray on the 2D detector with q = 0 Å-1 at the centre of the detector. The total q range for the instrument configuration outlined above was 0.02 < q < 1.06 Å-1. The mean lattice parameter, a, was calculated from d = 2π/q.

SAXS on equilibrium matrices

Bulk temperature scans (SI Figure 2) indicate that the addition of photochromics cause a small effect on phase transition behavior, but did not substantially affect the lattice parameters of the liquid crystal mesophases.

SI Figure 2. Temperature scans of bulk liquid crystal systems of (L à R) blank phytantriol, 2% (w/w) spiropyran, 2% (w/w) spirooxazine and 2% (w/w) spiropyran laurate. The phases formed are annotated.

UV source was an EXFO Acticure 4000 (Phoenix, AZ, USA) set at 350 nm and 60 mW power. White light source – 4 Ultrabright Nichia White LED (Blackburn, IL, USA).

UV irradiation experiments

Samples were irradiated with UV light (60 mW, 375 nm) for 60 second bursts and the liquid crystal structure observed using synchrotron SAXS over this time.

(A)
/ (B)

(C)
/ (D)

SI Figure 3. Time resolved SAXS plots showing response of phytantriol-water liquid crystal matrices containing (A) no photochromic, (B) 2% (w/w) SOX, (C) 2% (w/w) SP and (D) 2% (w/w) SPL. The matrices were exposed to 60 s of UV light (375 nm, 60 mW) and the mesophase structure followed over this time. Brighter shading indicates greater scattered intensity. The liquid crystal phase transitions are annotated on the right.

References

1. Raymo, F. i. M.; Giordani, S., J Am Chem Soc 2001, 123 (19), 4651-4652.

2. Darwish, T. A.; Evans, R. A.; Hanley, T. L., Dyes Pigments 2011, In Press.

3. Darwish, T. A.; Evans, R. A.; James, M.; Malic, N.; Triani, G.; Hanley, T. L., J Am Chem Soc 2010, 132 (31), 10748-10755.

4. Barauskas, J.; Landh, T., Langmuir 2003, 19 (23), 9562-9565.

5. Dong, Y.-D.; Dong, A. W.; Larson, I.; Rappolt, M.; Amenitsch, H.; Hanley, T.; Boyd, B. J., Langmuir 2008, 24 (13), 6998-7003.

6. Dong, Y.-D.; Larson, I.; Hanley, T.; Boyd, B. J., Langmuir 2006, 22 (23), 9512-9518.

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