S1

Supporting Information

Dynamic Behavior of Molecular Switches in Crystal under

Pressure and Its Reflection on Tactile Sensing

Yi Wang,† Xiao Tan,‡ Yu-Mo Zhang,† Shaoyin Zhu,† Ivan Zhang,† Binhong Yu,† Kai

Wang,‡ Bing Yang,† Minjie Li,*† Bo Zou,*‡ and Sean Xiao-An Zhang*†

† State Key Laboratory of Supramolecular Structure and Materials, Jilin University,

Changchun, Jilin 130012, China

‡State Key Laboratory of Superhard Materials, Jilin University, Changchun, Jilin

130012, China

S2

Table of Contents

Experimental details

Figure S1. Temperature-dependent 1H NMR spectra of OX-1 and OX-2 in different

solvents

Table S1. Kinetic parameters associated with the thermal ring opening of OX-1 and

OX-2 at 298 K

Table S2. Summary of crystal data and intensity collection parameters for OX-1,

OX-2 and IA-1

Figure S2. The absorption spectra of crystal OX-1 under ambient pressure with

Gaussian peak fitting

Figure S3. Kubelka-Munk diffuse reflectance absorption spectra of OX-1 and OX-2

powders under UV irradiation (high pressure mercury lamp, 500W) at different time

Figure S4. The optimized structures of neutral and zwitterionic isomers of OX-1 in

vacuum and the corresponding molecular volumes of two isomers with

B3LYP/6-31+G (d, p) calculations

Figure S5. The optimized structure of neutral and zwitterionic isomers of OX-2 in

vacuum with B3LYP/6-31G (d, p) calculations

Figure S6. Rough estimation of the ratio for neutral isomers of OX-1 in the

uncompressed pale-yellow crystal

Figure S7. Selected Raman spectra of OX-1 with increasing and decreasing pressure

in the wavenumber range of 50-1300 cm-1

Figure S8. Simulated Raman spectra for the neutral and zwitterionic isomers of OX-1

Figure S9. Rough estimation of neutral-to-zwitterionic transition ratio for OX-1

under compression

Figure S10. The evolution of absorption spectra of OX-1 crystal with time under

different pressure

Figure S11. Absorption spectra of OX-1 as a function of decreasing pressure

Figure S12. Raman spectra of OX-1 as a function of decreasing pressure in the

S3

wavenumber range of 1400-1800 cm-1

Figure S13. Frequency shifts of major Raman peaks of OX-2 as a function of

pressure (in the range of 0-10 GPa)

Figure S14. Real optical images, in-situ absorption and Raman spectra of OX-2 in the

range of 0-10 GPa

Figure S15. Real optical images, in-situ absorption and Raman spectra of OX-2 under

different pressure

Figure S16. Real optical images, in-situ absorption and Raman spectra of OX-1 in the

range of 0-18.14 GPa

Figure S17. The infrared spectra of OX-1 and OX-2 in uncompressed state and the

released state from 18 GPa

Figure S18. Optical images of ground OX-1 with different storage time and

absorption spectra of ground OX-1 with different heating time at 100 oC

Figure S19. Real optical images and in-situ absorption spectra of an IA-1 crystal with

increasing pressure

Figure S20. 1H NMR and

13C NMR of OX-1, OX-2 and IA-1

S4

Experimental details

Synthesis

OX-1 was synthesized according to reported literatures.S1

1H NMR

(300 MHz, CDCl3): δ (TMS, ppm): 7.98-7.94 (2H, m), 7.29 (2H, d,

J=9 Hz), 7.14-7.08 (2H, m), 6.86-6.83 (2H, t), 6.74-6.61 (4H, m), 6.15

(1H, d, J=16 Hz), 4.58 (2H, s), 2.96 (6H, s), 1.37 (6H, s); 13

C NMR

(75 MHz, CDCl3): δ (TMS, ppm):159.9, 151.0, 146.5, 140.5, 138.6,

136.3, 128.3, 127.7, 124.1, 123.8, 123.3, 122.4, 122.4, 120.9, 120.2, 118.4, 117.8,

112.3, 112.3, 109.0, 50.0, 40.9, 40.5, 40.5, 28.3, 14.3, 14.3. LC-HRMS: m/z calcd.

[M+H]+ 442.2125 found 442.2121.

OX-2 was synthesized according to reported literatures.S1

1H NMR

(300 MHz, CDCl3): δ (TMS, ppm): 8.19 (2H, d, J=9 Hz), 8.01-7.98

(2H, m), 7.54 (2H, d, J=9 Hz), 7.15-7.10 (2H, m), 6.91-6.86 (3H, m),

6.64 (1H, d, J=8 Hz), 6.55 (1H, d, J=16 Hz), 4.63 (1H, d, J=17 Hz),

4.55 (1H, d, J=17 Hz), 1.56 (3H, s), 1.25 (3H, s); 13

C NMR (75 MHz,

CDCl3): δ (TMS, ppm):158.8, 147.6, 146.2, 141.7, 140.9, 137.8, 134.1, 129.3, 127.9,

127.5, 124.2, 124.1, 123.3, 122.4, 121.0, 120.0, 119.8, 117.7, 108.9, 103.2, 50.5, 40.8,

26.7, 18.7, 18.7. LC-HRMS: m/z calcd. [M+H]+ 444.1554 found 444.1558.

Compounds of 2,3,3-trimethyl-3H-indole (0.636 g, 4 mmol) and

4-(dimethylamino)benzaldehyde (0.715 g, 4.8 mmol) were refluxed in anhydrous

alcohol (20 ml) with methylsulphonic acid (0.1 ml, 1.5 mmol) as catalyst for 22 hours.

Then the mixture was neutralized with saturated Na2CO3 solution and extracted with

ethyl acetate. The organic layer was concentrated under reduced pressure, and the

residue was purified by column chromatography [SiO2: hexane / ethyl acetate (20:1)]

to afford IA-1 (0.28 g, 24%) as a yellow solid. 1H NMR (300 MHz, CDCl3): δ (TMS,

ppm): 7.68 (1H, d, J=18 Hz), 7.59 (1H, J=6 Hz), 7.51 (2H, d, J=9 Hz), 7.31-7.21 (2H,

m), 7.19 (1H, m), 6.87 (1H, d, J=16 Hz), 6.70 (2H, d, J=9 Hz), 3.02 (6H, s), 1.45 (6H,

s); 13

C NMR (75 MHz, CDCl3): δ (TMS, ppm): 183.9, 154.2, 151.1, 146.4, 138.4,

128.9, 128.9, 127.6, 124.8, 123.9, 120.9, 120.0, 114.8, 112.0, 112.0, 52.4, 40.1, 40.1,

24.0, 24.0. LC-HRMS: m/z calcd. [M+H]+ 291.1856 found 291.1863.

S5

Characterization

1H NMR and

13C NMR spectra were recorded on a Varian Mercury using TMS as a

standard at room temperature. LC-HRMS analysis was performed on an Agilent

1290-microTOF-Q II mass spectrometer. UV-Vis absorption spectra were measured

using a Shimadzu UV-2550 PC double-beam spectrophotometer. Single-crystal X-ray

diffraction data was recorded on a Rigaku RAXIS-PRID diffractometer using the

ω-scan mode with graphite-monochromator Mo·Kα radiation (λ = 0.71073 Å).

Kubelka-Munk diffuse reflectance absorption spectra were performed on a Maya

2000PRO fiber optical spectrometer with Ocean DH-2000-BAL UV-Vis-NIR light

source using BaSO4 as background. IR spectra studies were performed on Vertex

80/80V FT-IR spectrometer over the range of 4000-400 cm-1

.

High-pressure experiments were carried out using a diamond anvil cell (DAC)

(detailed descriptions shown as follow). The culet diameter of the diamond anvils was

0.5 mm. T301 stainless steel gaskets were preindented to a thickness of 60 μm, and

center holes of 0.16 mm were drilled for the sample. The ruby chip was used for

pressure determination using the standard ruby fluorescent technique. Silicone oil was

used as the pressure-transmitting medium. All experiments were performed at room

temperature. High-pressure unpolarized Raman spectra were recorded using Acton

SP2500i spectrometer (Princeton Instruments) equipped with the liquid nitrogen

cooled CCD (PyLon: 100B). The 532 nm radiation from the diode pumped solid state

(DPSS) laser was utilized to excite the sample and the output power was 10 mW.

High-pressure absorption spectra were recorded by an optical fiber spectrometer

(Ocean Optics, QE65000). The real optical images were obtained by using a Nikon

Ti-U microscope equipped with a digital color camera.

Schematic diagram of diamond anvil cell (DAC)

S6

Figure S1. (a) The tautomerization of benzo[1,3]oxazines OX-1 and OX-2 between

neutral and zwitterionic isomers; (b) partial 1H NMR spectra of OX-1 in chloroform-d

at different temperatures; (c) partial 1H NMR spectra of OX-1 in acetonitrile-d3 at

different temperatures; (d) partial 1H NMR spectra of OX-2 in chloroform-d at

different temperatures.

As shown in Figure S1a, the chiral center at the junction of the two heterocycles in

neutral OX-1 will impose two distinct environments on the pair of indoline methyl

groups and on the two oxazine methylene protons with two singlets for the methyl

protons (MeO and Me

□) and AB system for the methylene protons (H

O and H

□).

However, such 1H NMR spectra were only observed under lower temperatures

(Figure S1b and S1c), which indicate that a fast interconversion between the two

enantiomers of OX-1 on the 1H NMR time scale exists in solutions at ambient

conditions. This phenomenon is the same as other benzo [1, 3] oxazines reported by

Raymo in 2005.S2

a

b

S7

c

d

Table S1. Kinetic parameters associated with the thermal ring opening of OX-1 and

OX-2 at 298 K.

The rate constant (k), free energy (△G≠), enthalpy (△H

≠), and entropy (△S

≠) of

activation were determined by variable-temperature 1H NMR spectroscopy.

S2

compound solvent k (s-1

) △G≠

(kcal mol-1) △H≠

(kcal mol-1) △S≠

(kcal mol-1K-1)

OX-1 chloroform-d 24766.01 11.51 19.26 0.026

OX-1 acetonitrile-d3 8400.04 12.04 14.96 0.010

OX-2 chloroform-d 2.31 16.86 19.82 0.010

S8

Table S2. Summary of crystal data and intensity collection parameters for OX-1,

OX-2 and IA-1.

Compound OX-1 OX-2 IA-1

Formula

Formula mass

Space group

a/ Å

b/ Å

c/ Å

α/o

β/o

γ/o

V/Å3

Z

ρ/g.cm-3

F000

Temp, (K)

Absorption coefficient, μ/mm-1

No. of reflections measured

No. of independent reflections

Rint

Final R1 values (I > 2σ(I))

Final wR(F2) values (I > 2σ(I))

Final R1 values (all data)

Final wR(F2) values (all data)

Goodness of fit on F2

CCDC numbers

C27 H27N3O3

441.52

C2/c

24.174(11)

10.013(5)

19.969(9)

90

100.132(19)

90

4758(4)

8

1.233

1872.0

296(2)

0.081

18154

4183

0.0277

0.0592

0.1714

0.0805

0.1875

1.005

922651

C25 H21N3O5

443.45

P2(1)/c

14.314(3)

13.075(3)

12.034(2)

90

109.95(3)

90

2117.2(7)

4

1.391

928

153(2)

0.099

19794

4800

0.0719

0.0549

0.1217

0.1039

0.1419

1.018

1015010

C20H22N2

290.40

P21/c

17.115(3)

5.9160(12)

16.611(4)

90

94.76(3)

90

1676.1(6)

4

1.151

624.0

296(2)

0.068

14175

3810

0.0486

0.0534

0.1217

0.1086

0.1464

0.967

1015011

S9

OX-1

OX-2

IA-1

Single-crystal X-ray structure of OX-1, OX-2 and IA-1 (50% probability ellipsoids)

S10

Figure S2. The absorption spectra of crystal OX-1 under ambient pressure with

Gaussian peak fitting.

Figure S3. Kubelka-Munk diffuse reflectance absorption spectra and real optical

images of OX-1 (a) and OX-2 (b) powders under UV irradiation (high pressure

mercury lamp, 500W) at different time.

S11

Figure S4. The optimized structures of neutral and zwitterionic isomers of OX-1 in

vacuum and the corresponding molecular volumes of two isomers with

B3LYP/6-31+G (d, p) calculations.S3

The simulation results show that the neutral

isomer is more stable with 9.17 kcal•mol-1

in energy lower than that of zwitterionic

one. But the dipole moment of zwitterionic isomer of OX-1 is around twice larger

than that of neutral one.

Molecular volume Neutral isomer Zwitterionic isomer

OX-1 338.652 cm3•mol

-1 374.610 cm

3•mol

-1

Figure S5. The optimized structures of neutral and zwitterionic isomers of OX-2 in

vacuum with B3LYP/6-31G (d, p) calculations.S3

The simulation results show that the

neutral isomer is more stable with 18.28 kcal•mol-1

in energy lower than that of

zwitterionic one.

S12

Figure S6. Rough estimation of the ratio for neutral isomers of OX-1 in the

uncompressed pale-yellow crystal: (a) absorption spectra of OX-1 in acetonitrile

solutions with different concentrations (inset: the absorbance of the peak at 306 nm

with different concentrations), (b) absorption spectra of IA-2 in acetonitrile solutions

with different concentrations (inset: the absorbance of the peak at 540 nm with

different concentrations).

Because two isomers of OX-1 are always co-existing (Figure S6a), it is difficult to

transform the all neutral isomers into zwitterionic forms in solution. Considering

structural similarity, we utilize IA-2 to estimate the molar absorption coefficient of

zwitterionic isomer of OX-1. According to a series of acetonitrile solutions with

different concentrations (Figure S6a and b), we can obtain molar absorption

coefficients of neutral and zwitterionic isomers of OX-1 are 3.60×106

and 8.61×

106

L•m-1

•mol-1

, respectively. For uncompressed crystal OX-1, the absorbances of

neutral and zwitterionic isomers of OX-1 are around 0.07 and 0.015 (Figure 3b),

respectively. We assume that the molar absorption coefficients of the two isomers are

constant in solution and solid states and the light path are the same for the two

isomers. In addition, we also assume that the Lambert-Beer law is suitable for this

system. According to the Lambert-Beer law: A=Ɛ•b•c, we can obtain the

concentrations of neutral and zwitterionic isomers with the values of 0.07/(b*3.60*106)

and 0.015/(b*8.61*106), respectively. Therefore, we can conclude neutral isomers of

OX-1 in uncompressed pale-yellow crystal is around 92% according to following

function:

[0.07/(b*3.60*106)]/[0.07/(b*3.60*10

6)+ 0.015/(b*8.61*10

6)]

S13

Figure S7. Selected Raman spectra of OX-1 as a function of increasing (a) and

decreasing (b) pressure in the wavenumber range of 50-1300 cm-1

. Owing to the

interference of strong background fluorescence, they are too weak to be reliably used

for structural analysis.

S14

Figure S8. The simulated Raman spectra for the neutral (a) and zwitterionic (b)

isomers of OX-1 with B3LYP/6-31+G (d, p) calculations.S3

a

As shown in Figure S8a, calculation results show that the neutral isomer of OX-1

has two main peaks (1660.09 cm-1

and 1705.89 cm-1

) in the range of 1500-1750cm-1

.

They are assigned to the two different vibration modes of isolated π-system of N,

N-dimethyl-4-vinyl benzenamine (Supporting information, Video 1). Experimentally,

there are only two main peaks at 1608 cm-1

and 1647 cm-1

in the Raman spectra at 0

GPa (Figure 3c and S9), so we assign these two peaks to the characteristic vibrations

of the neutral isomer of XO-1, because the ratio of zwitterionic isomer is low and

their Raman spectra are very weak at 0 GPa.

S15

b

As shown in Figure S8b, calculation results show that the zwitterionic isomer of

OX-1 has five main peaks in the range of 1450-1700cm-1

, and they are assigned to the

extended conjugated π-systems of cyanine and nitrophenolate in zwitterionic isomer

(Supporting information, Video 1). Thus, we assign the two increasing broad peaks

with pressure at around 1540 cm-1

and 1480 cm-1

in experimental spectra to the

vibration of zwitterionic isomer (Figure 3c and S9). Accordingly, the Raman peak

intensity at 1647 cm-1

decreases with pressure, indicating the neutral to zwitterionic

transition. But for the intensity at 1608cm-1

, it should decrease synchronously with the

peak at 1647 cm-1

, because they are from the same group of N, N-dimethyl-4-vinyl

benzenamine of neutral OX-1. However, the intensity at 1608 cm-1

seems invariable

with pressure, which is because it overlaps with two of the increasing Raman peak for

the zwitterionic isomer (1630.28 cm-1

and 1648.94 cm-1

in calculation).

S16

Figure S9. Rough estimation of neutral-to-zwitterionic transition ratio for OX-1

under compression: (a) in-situ Raman spectra of an OX-1 crystal in DAC with

increasing pressure; (b) the ratio of neutral isomer of OX-1 in the crystal with

increasing pressure.

According to the simulated Raman spectra (Figure S8a), two strong peaks at 1608

cm-1

and 1647 cm-1

are assigned to two different vibration modes of isolated

π-systems of N, N-dimethyl-4-vinyl benzenamine in neutral isomer. In addition, the

peak at 1647 cm-1

is not overlapped with the peaks of zwitterionic isomer and its

change with pressure is quite obvious from strong to almost vanished, so we choose

its peak intensity to represent the concentration of neutral isomer. S4

Because the peak

at 1608 cm-1

is the overlapped results of neutral and zwitterionic isomers (Figure S8b),

the decreased peak intensity of neutral isomer could be supplemented by

newly-formed zwitterionic isomer because of their similar Raman activity

(Supporting information, Video 1), as a result, the peak at 1608 cm-1

could be

considered roughly as a constant in the whole compression (Figure S9a). Therefore,

we take the peak at 1608 cm-1

as an internal standard to eliminate error in different

measurements. We could obtain a good linear relation between ratios of neutral

isomer of OX-1 and pressure (Figure S9b). And the results show that the proportion

of zwitterionic isomers increases from 8% to 83% when the pressure is increased to

10.18 GPa.

Calculation details:

Column (A) Column (B) Column (C)

Pressure Relatively peak intensity Ratio of neutral isomer

0 GPa 1.32 0.92

0.99 GPa 1.29 0.90

2.00 GPa 1.10 0.77

3.09 GPa 0.82 --

S17

Note:

(1) The relatively peak intensity is obtained through the peak intensity at 1647 cm-1

divided by the peak intensity at 1608 cm-1

.

(2) In addition, the relatively peak intensity at 3.09 GPa is much deviated from the

others, so we ignored this pressure point when we plotted the ratios of neutral

isomer with pressure.

(3) Ratio of neutral isomer is calculated by as following function, where 1.32 is the

relatively peak intensity at 0 GPa and 0.92 is the ratio of neutral isomer at 0 GPa

(Figure S6):

(Column (B)/1.32)*0.92

4.00 GPa 0.96 0.67

4.96 GPa 0.77 0.54

5.95 GPa 0.68 0.47

7.09 GPa 0.58 0.40

8.09 GPa 0.38 0.26

9.08 GPa 0.32 0.22

10.18 GPa 0.24 0.17

S18

Figure S10. The evolution of absorption spectra of OX-1 crystal with time under

different pressure.

Figure S11. Absorption spectra of OX-1 as a function of decreasing pressure.

S19

Figure S12. Raman spectra of OX-1 as a function of decreasing pressure in the

wavenumber range of 1400-1800 cm-1

.

Figure S13. Frequency shifts of major Raman peaks of OX-2 as a function of

pressure (in the range of 0-10 GPa).

S20

Figure S14. Molecular structure of OX-2 in neutral form, and real optical images of

an OX-2 crystal with increasing and decreasing pressure (a) (the balls at upper right

corner in DAC are ruby pressure markers). In-situ absorption spectra of an OX-2

crystal in DAC with increasing pressure (b) and decreasing pressure (c) (inset:

comparison of the absorption spectra of OX-2 in the uncompressed and released

states). In-situ Raman spectra of an OX-2 crystal in DAC with increasing pressure (d)

and decreasing pressure (e) (inset: comparison of the Raman spectra of OX-2 in the

uncompressed and released states).

S21

Figure S15. Real optical images (a), in-situ absorption spectra (b) and Raman spectra

(c) of an OX-2 crystal under different pressure.

S22

Figure S16. Optical images of an OX-1 crystal with increasing and decreasing

pressure (0-18.14 GPa), the balls at upper right corner in DAC are ruby pressure

markers (a). In-situ absorption spectra of an OX-1 crystal in DAC with increasing

pressure (b). Comparison of the absorption spectra of OX-1 in the uncompressed and

released states (c). In-situ Raman spectra of an OX-1 crystal in DAC with increasing

pressure (d). Comparison of the Raman spectra of OX-1 in the different states (e).

Though the color of OX-1 crystal remained black (Figure S16a), its absorption spectra

continuously shifted to longer wavelength (Figure S16b) and the broadening Raman peaks

assigned to the zwitterionic isomer (the second set) also shifted to higher frequency (Figure S16d)

when the crystal was further compressed to 18 GPa. When the pressure was removed, the crystal

of OX-1 could not recover to the original state from both optical images, absorption and Raman

spectra (Figure S16a, c, and e). Especially in the recovered Raman spectra of OX-1 (Figure S16e),

there are only three Raman peaks that are similar to the zwitterionic isomer. This indicates

irreversible chemical reaction of OX-1 happens (Figure S17).

S23

Figure S17. The infrared spectra of OX-1 in uncompressed state (a) and the released

state from 18 GPa (b). The infrared spectra of OX-2 in uncompressed state (c) and the

released state from 18 GPa (d).

According to literatures,S5-S6

the polymerization of benzene involves the ring-opening

of benzene ring and transforms sp2 carbon atom into sp

3 one, which results in the

absorption intensity change for the saturated C-H. By comparing the infrared spectra

of OX-1 and OX-2 in the uncompressed state and released state from 18 GPa, we find

that relative peak intensities of the saturated C-H (2964 cm-1

) to aromatic ring (1608

cm-1

) in the released sample of OX-1 greatly increased (Figure S17a and b), which

clearly shows the polymerization of aromatic ring in highly compressed OX-1. A

similar phenomenon is also observed in OX-2 (Figure S17c and d). Considering the

critical threshold distance of C…C distance (2.6 Å) for the polymerization benzene

ringsS5

and the fact that there are relatively good π…π interactions in the crystal of

OX-1 and OX-2 (3.991 Å and 3.386 Å) (Figure 1), we think it’s reasonable to deduce

that the irreversible polymerization takes place between these interacted aromatic

rings.

S24

Figure S18. Optical images of ground OX-1 with different storage time (a):

immediately after they are ground (left), stored for one year under ambient conditions

(right); absorption spectra of ground OX-1 with different heating time at 100 oC (b).

a b

Figure S19. Molecular structure of IA-1 and real optical images of an IA-1 crystal

with increasing pressure (two balls under the crystal is ruby pressure markers) (a),

in-situ absorption spectra of an IA-1 crystal in DAC with increasing pressure (b).

S25

Figure S20. 1H NMR and

13C NMR of OX-1, OX-2 and IA-1

OX-1

S26

OX-2

S27

IA-1

S28

Reference

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113, 8491-8497.

S2 (a) Nelson, J. H. Nuclear Magnetic Resonance Spectroscopy; Prentice Hall: Upper Saddle

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S4 Ni, B. B.; Wang, K.; Yan, Q.; Chen, H.; Ma, Y.; Zou, B. Chem. Commun. 2013, 49,

10130-10132.

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6, 39-43.

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