Supplementary Information for:

Light-Responsive Spiropyran based Polymer Thin

Films for Use in Organic Field-Effect Transistor

Memories

Yong Jin Jeong,a Eun Joo Yoo,b Lae Ho Kim,a Seonuk Park,a Jaeyoung Jang,c Se Hyun

Kim,b,*, Seung Woo Lee,b,*and Chan Eon Park,a,*

a Polymer Research Institute, Department of Chemical Engineering, Pohang University of

Science and Technology, Pohang, 790-784, Korea.

b School of Chemical Engineering, Yeungnam University, Gyeongsan, North Gyeongsang

712-749, South Korea

c Department of Energy Engineering, Hanyang University, Seoul, 133-791, South Korea

Corresponding author information

*E-mail: cep@postech.ac.kr, Fax: +82-54-279-8298, Tel: +82-54-279-2269 (C. E. Park)*E-mail: shkim97@yu.ac.kr, Fax: +82-53-810-4686, Tel: +82-53-810-2779 (S. H. Kim)*E-mail: leesw1212@ynu.ac.kr, Fax: +82-53-810-4631, Tel: +82-53-810-2516 (S. W. Lee)

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C.This journal is © The Royal Society of Chemistry 2016

Synthetic methods and analysis of 6FDA-DBA-SP

Synthesis of soluble polyimide: A soluble polyimide backbone of spiropyran compound

(6FDA-DBA) was prepared from 6FDA and DBA as followsS1. Equimolar amounts of 6FDA

(4.00 g, 9.00 mmol) and DBA (1.37 g, 9.00 mmol) were dissolved together with a catalytic

amount of isoquinoline in dry NMP. The solution was heated gently with stirring at 80 C for

2 h and then refluxed with stirring at 240 C for 12 h. The reaction solution was then poured

into a mixture of methanol with vigorous stirring, giving the polymer product in precipitated

powder. The precipitated powder was filtered, washed several times with the mixture solvent,

and dried in a vacuum oven at 50 C.

Synthesis of spiropyran derivative: Spiropyran derivative, SP-OH, was prepared by modified

according to the previous literature.S2,S3 A mixture of 2,3,3-trimethyl-3H-indole (6.00 g, 37.68

mmol) and 2-bromoethanol (6.12 g, 48.99 mmol) was heated to 240 C for 6 h under N2. After

cooling to room temperature, the crude product was suspended in chloroform and the mixture

was sonicated and filtered. The precipitation was recrystallized from ethyl acetate, and dried to

give 1-2(-hydroxyethyl)-2,3,3-trimethyl-3H-indolium bromide (9.50 g, 88.7% yield), which

was then used in the next step without purification. A solution of 1-2(-hydroxyethyl)-2,3,3-

trimethyl-3H-indolium bromide (8.00 g, 28.15 mmol) and KOH (3.60 g, 64.18 mmol) in

distilled water was stirred at room temperature for 1 hr and extracted with Et2O. The organic

layer was collected, dried with MgSO4, and concentrated under reduced pressure to afford 3,3-

dimethyl-1-(2-hydroxyethyl)-indoline (4.72 g, 82.4% yield) as a yellow oil. A mixture of 3,3-

dimethyl-1-(2-hydroxyethyl)-indoline (4.00 g, 19.68 mmol) and 5-nitrososalicylaldehyde (3.41

g, 19.68 mmol) in ethanol was heated for 3 h under reflux in a N2 atmosphere. After cooling to

room temperature, the precipitation was filtered, washed with ethanol, and dried to give 2-

(3′,3′-dimethyl-6-nitrospiro[chromene-2,2′-indolin]-1′-yl)ethanol, SP-OH, as a purple solid

(5.58 g, 74.65 yield). The synthetic process was summarized in Scheme 1.

N

OH

B rNN

OH

N

OH

O NO2

Scheme 1. Synthesis route and chemical structures of 2-(3′,3′-Dimethyl-6-

nitrospiro[chromene-2,2′-indolin]-1′-yl)ethanol

Synthesis of polyimide with spiropyran as a side group: A soluble polyimide with

spiropyran as a side group, 6FDA-DBA-SP, was synthesized from the reaction of 6FDA-DBA

and SP-OH.S4 A mixture of 6FDA-DBA, SP-OH, EDAC, and DMAP (1:3:3:3 in molar ratio)

in methylene chloride (total amount of the reactants was 10 wt. %) was stirred at room

temperature for 24 h under N2. The reaction mixture was precipitated in methanol with vigorous

stirring at room temperature, filtered, washed several times with methanol, and then dried in a

vacuum oven at 80 C to give 6FDA-DBA-SP.

Measurements: The synthesized 6FDA-DBA and 6FDA-DBA-SP were dissolved in

dimethyl-d6 sulfoxide (DMSO-d6) and characterized by using a proton nuclear magnetic

resonance (NMR) spectrometer (Bruker, DPX300). Their molecular weights were measured

by using a gel permeation chromatography (GPC) system (PL-GPC 210, Polymer Labs)

calibrated with polystyrene standards. In these measurements a flow rate of 1.0 mL/min was

employed and THF was used as the eluent. The glass transition temperatures (Tg) of the films

of the two polymers were measured in the range 25-400 °C using a differential scanning

calorimeter (DSC) (DSC-60, Shimadzu). During the measurements, dry nitrogen gas was used

for purging; a flow rate of 80 cm3/min and a ramping rate of 10.0 °C/min were employed. In

each run, a sample of about 5 mg was used. The value of Tg was taken as the onset temperature

of the glass transition in the thermogram. The degradation temperatures (Td) of the polymer

films were measured in the range 50-800 °C using a thermogravimeter (DTG-60H, Shimadzu).

During these measurements, dry nitrogen gas was used for purging; a flow rate of 100 cm3/min

and a ramping rate of 5.0 °C/min were employed.

The characterization results of synthesized 6FDA-DBA-SP polymers

6FDA-DBA-SP was synthesized in two major steps: synthesis of soluble 6FDA-DBA

polyimide followed by incorporation of SP side groups into the polymer. Soluble 6FDA-DBA

was synthesized directly from the polycondensation of the respective monomers using

isoquinoline as a catalyst. The obtained polymer was characterized by 1H NMR spectroscopy.

In the 1H NMR spectrum (Fig. S1(a))), the proton peak of the carboxylic acid side groups

appears at 13.5 ppm, while the proton peaks of the aromatic rings on the polymer backbone

appear in the range 7.7-8.3 ppm. Amino protons originating from possible residues of partially

imidized 6FDA-DBA poly(amic acid) were not detected. This polyimide polymer was

measured to have a weight-averaged molecular weight (Mw) of 29,600 and a polydispersity

(PDI) of 1.87 by GPC analysis. SP side groups were incorporated in the soluble 6FDA-DBA,

giving 6FDA-DBA-SP. As shown in Fig. S1(b), the 1H NMR spectrum of 6FDA-DBA-SP does

not show any peaks originating from the carboxylic acid groups of 6FDA-DBA. From the

integration of the characteristic proton peak of spiropyran and 6FDA-DBA, the conversion

yield of the CI incorporation reaction is estimated to be 98%. These results indicate that the

carboxylic acid groups of the 6FDA-DBA have almost completely reacted with SP-OH, giving

6FDA-DBA-SP. The molecular weight of synthesized 6FDA-DBA-SP is estimated to have

38,600 Mw and a PDI of 1.86.

Figure S1. 1H-NMR spectrum of (a) 6FDA-DBA and (b) 6FDA-DBA-SP.

Fig. S2 shows the DSC and thermogravimetric analysis (TGA) thermograms of 6FDA-DBA

and 6FDA-DBA-SP films. The 6FDA-DBA film was found to have a Tg of 312 °C and a Td of

390 °C, whereas the 6FDA-DBA-SP film had a Tg of 173 °C and a Td of 212 °C. Overall, the

values of Tg and Td of the 6FDA-DBA were lowered. It resulted from the incorporation of

spiropyran side groups that had lower Tg and Td.

Figure S2. DSC (upper graph) and TGA (lower graph) results of 6FDA-DBA and 6FDA-DBA-

SP, respectively.

Fig. S3 shows the UV absorption spectra of SP-OH, 6FDA-DBA and 6FDA-DBA-SP

measured in 1,4-dioxane solution. SP-OH exhibit an absorption maximum at 334 nm (=λmax).

The 6FDA-DBA-SP showed broad shoulder absorbance, which is due to the spiropyran

chromophores in the side groups.

300 350 400 450 5000.00

0.25

0.50

0.75

1.00

6FDA-DBA (without spiropyran)

Abso

rban

ce (a

.u.)

Wavelength (nm)

SP-OH6FDA-DBA-SP

Figure S3. UV-Vis absorption spectra of SP-OH, 6FDA-DBA, and 6FDA-DBA-SP. .

Reference

S1. Lee, S. W.; Kim, S. I.; Lee, B.; Choi, W.; Chae, B.; Kim, S. B.; Ree, M. Macromolecules,

2003, 36, 6527.

S2. Zhu, M. Q.; Zhang, G. F.; Hu, Z.; Aldred, M. P.; Li, C.; Gong, W. L.; Chen, T.; Huang, Z.

L.; Liu, S. Macromolecules, 2014, 47, 1543.

S3. Raymo, F. M.; Giordani, S. J. Am. Chem. Soc. 2001, 123, 4651.

S4. Fihey, A; Perrier, A.; Browne, W. R.: Jacquemin, D. Chem. Soc. Rev. 2015, 44, 3719.

-40 -20 0 20 4010-1310-1210-1110-1010-910-810-710-610-510-4

VG (V)

VD = -40 V

01234567

|I D|1/2 (A

)1/2 X

103

|I D| (A)

Figure S4. (a) Transfer characteristics in the saturation regime (VD = -40 V) of SP-OFETs,

operated in forward (40 V to -40 V) and backward (-40 V to 40 V) scans of VG.

Table S1. Electrical characteristics of the SP-OFETs calculated from Fig. S2a

Ci [nF/cm2] µsat [cm2/Vs] Vth [V] Von [V] Ion/off

22.2 0.37 -7.2 -1 ~ 106

Ci = Capacitance of 20 nm-thick 6FDA-DBA-SP/ 100 nm-thick SiO2 bilayer

The field-effect mobility (μ) in the saturation regime (drain voltage, VD = - 40 V) was

calculated from the slope of square root drain current ( ) versus gate voltage ( ) using the I1/2D VG

following equation:

𝐼𝐷 =μCiW

2L(VG – Vth)2 (1)

where Ci is the capacitance per unit area of the gate dielectrics and Vth is the threshold voltage.

-40 -20 0 20 4010-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

VD = -10 V

Initial (dark) 2nd (dark) 3rd (dark) 4th (dark) 5th (dark) 6th (dark) 7th (dark) 8th (dark) 9th (dark) 10th (dark) Under light

VG (V)

|I D| (A)

Figure S5. Transfer characteristics of the SP-OFETs during successive sweeps under different

conditions (10 sweeps in dark conditions – 1 sweeps under white-light).

-60 -50 -40 -30 -20 -10 0 10 20-202468

10121416 Dark condition

VG (V)

|I D| (A

)

Initial -20 V -30 V -40 V -50 V

-40 -20 0 2002468

1012141618

Dark condition -40 V for 10ms -40 V for 100ms -40 V for 1s -40 V for 10s

VD = -10 V

|I D| (A

)

VG (V)

(a) (b)

Figure S6. (a) Transfer characteristics of SP-OFETs as a function of applied bias time in dark

condition. The VG of -40 V was applied. (b) Transfer characteristics of SP-OFETs as a function

of applied bias voltage in dark condition. The bias was applied for 10 ms.

We investigated the negative shifts of transfer curves according to applied bias time and

bias voltages. The transfer curves in Fig. Sx(a), revealed that 10 ms was time enough to trap

most holes within 6FDA-DBA-SP layers and induced transfer curve shifts after appling VG of

-40 V bias in dark condition. We could check negative shifts of transfer curves depending on

increasing bias time. Since p-type pentacene semiconductor had much higher hole densities

than electron densities, the electric field at the pentacene/6FDA-DBA-SP interfaces by

applying VG of -40 V bias enabled to trap the existed holes from pentacene into 6FDA-DBA-

SP layers in a short period of time. It showed, therefore, tiny changes (ΔVon < 2 V) in transfer

curve depending on various applied bias times of 10 ms, 100 ms, 1 s, and 10 s.

The effects of applied electric field at the pentacene/6FDA-DBA-SP interfaces on

transfer curve shifts were investigated by applying a variety of bias voltages, as shown in Fig.

Sx(b). Applying VG of -20 V bias formed transverse electric field not enough to induce hole

trapping into 6FDA-DBA-SP layers, thereby not showing any transfer curve shifts. Higher

negative electric field by applying more extensive bias stress (VG of -50 V), on the other hand,

shifted the transfer curves toward more negative direction compared to those under applying

VG of -40 V because more holes were attracted to dielectric layers under high transverse electric

field.

-40 -20 0 20-202468

101214161820

Under white-light

initial (dark) -40 V for 10ms -40 V for 100ms -40 V for 1s -40 V for 10s

VD = -10 V

|I D| (A

)

VG (V)

Figure S7. (a) Transfer characteristics of SP-OFETs as a function of applied bias time under

white-light illumination (sweeping from -40 V to 40 V). The VG of -40 V was applied.

-40 -20 0 20 4010-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

Initial 40V 1min under light 50V 1min under light 60V 1min under light

VD = -10 V

VG (V)

|I D| (A)

polystyrene

-40 -20 0 20 4010-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

6FDA-DBA-SP

VD = -10 V

Initial 40V 10sec under light

|I D| (A)

VG (V)

(b) (c)

(a)

-40 -20 0 20 4010-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

polystyrene

VD = -10 V

VG (V)

|I D| (A)

Dark condition Under light

Figure S8. (a) Transfer characteristics of pentacene OFETs based on polystyrene electret layer

under dark conditions or under white-light illumination, operated under forward (40 to –40)

and backward (–40 to 40) VG scans. Shift in the transfer curves of pentacene OFETs based on

(b) polystyrene electret layer and (c) 6FDA-DAB-SP layer under light-assisted programming

bias.

4.0 4.5 5.0 5.5 6.0 6.5 7.0

In

tens

ity (a

. u.)

Kinetic Energy (eV)

6FDA-DBA-SP (dark) 6FDA-DBA-SP (light)

pentacene on 6FDA-DBA-SP (dark) pentacene on 6FDA-DBA-SP (light)

(b)

(a)

84 86 88 90 92

89.4 eV

6FDA-DBA-SP (dark) pentacene 20 nm (dark)

Inte

nsity

(a. u

.)

Kinetic Energy (eV)

Ef

88.44 eV

84 86 88 90 92

89.36 eV

6FDA-DBA-SP (light) pentacene 20 nm (light)

Inte

nsity

(a. u

.)

Kinetic Energy (eV)

Ef

88.25 eV

Figure S9. Comparative UPS spectra showing (a) secondary cutoff region and (b) valence

regions of pentacene/6FDA-DBA-SP film and 6FDA-DBA-SP film under dark environment

or white-light illumination. The energy of light source in the UPS was 90 eV.

(a) (b)

2.0 2.5 3.0 3.5 4.0 4.5 5.0

h (eV)

Eg = 3.65 eV

(h (a

. u.)

0 s 30 s 60 s 90 s 120 s

1.6 1.8 2.0

pentacene

h (eV)

Eg = 1.82 eV

(h (a

. u.)

Figure S10. (αhv)2 versus hv plot for determining the bandgap of (a) 6FDA-DBA-SP and (b)

pentacene film. The (a) plot shows (αhv)2 versus hv of 6FDA-DBA-SP according to UV light

illumination time

The fermi energy level and vacuum level shift were calculated from using the secondary

cutoff region of UPS spectra, the highest occupied molecular orbital (HOMO) levels were

calculated from the fermi energy level and valence regions of UPS spectra, and the lowest

unoccupied molecular orbital (LUMO) levels were calculated using the HOMO levels and the

band gap energy measured directly from the onset of (αhv)2 versus hv plot. The electron

injection barrier between pentacene and 6FDA-DBA-SP could be calculated from the

difference between the LUMO levels of pentacene and 6FDA-DBA-SP.

10-1310-1110-910-710-510-310-1101103

Readin

gEra

sing

Readin

gWriti

ng

Under light Dark condition

Under light Dark condition

V G (V)

|I D| (A)

-200

-150

-100

-50

0

50

Figure S11. Comparison of current response to one-cycle switching behavior of SP-OFET

memory devices after light-assisted programming (40 V under white-light) or programming

without light illumination (40 V in dark environment).

-10 -5 0 5 1010-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

|I D| (A)

VG (V)

Number of bends 0 10 100 300 500

Figure S12. Transfer characteristics (VD = -5 V) of the flexible SP-OFETs before and after 10,

100, 300, and 500 times bending under dark condition.