From Homochiral Assembly to Heterochiral Assembly: A Leap in

Subscriber access provided by OCCIDENTAL COLL

New Concepts at the Interface: Novel Viewpoints and Interpretations, Theory and Computations

From Homochiral Assembly to Heterochiral Assembly: A Leap in Charge Transport Properties of Binaphthol-based Axially Chiral Materials Ming Chen, Xuechen Jiao, Jing Li, Wenting Wu, Hanshen Xin, Christopher R. McNeill, and Xike Gao Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.9b00463 • Publication Date (Web): 12 Apr 2019 Downloaded from http://pubs.acs.org on April 14, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

From Homochiral Assembly to Heterochiral Assembly: A Leap in Charge Transport Properties of Binaphthol-based Axially Chiral Materials Ming Chen,† Xuechen Jiao,‡ Jing Li,† Wenting Wu,† Hanshen Xin,† Christopher R. McNeill,*‡ and Xike Gao*† †

Key Laboratory of Synthetic and Self-Assembly Chemistry for Organic Functional Molecules,

Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China ‡Department

of Materials Science and Engineering Monash University, Victoria 3800, Australia.

ABSTRACT: Chirality, as a fundamentally asymmetric property, plays an important role in molecular assembly in the solid state, impacting upon the properties and performance of organic materials. Here, heterochiral assembly was observed upon a binaphthol-based axially chiral material in thin film state, where the heterochiral assemblies of racemic mixtures exhibit superior crystallization behavior and film morphologies than their homochiral counterparts. Additionally, a dramatic increase (nearly two orders of magnitudes) in electronic mobility was obtained upon switching the active layers of organic thin film transistors from homochiral assemblies to heterochiral assemblies. This work not only gives insights into the structure–aggregation property

ACS Paragon Plus Environment

1

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 24

relationships of axially chiral self-assemblies, but also offers new opportunities for novel organic soft materials.

INTRODUCTION Molecular chirality controls the asymmetrically spatial interactions of molecules and further impact the enantioselectivity of chemical reactions,1−3 molecular recognition4−6 and assembly behavior of molecular components.7−11 Since the pioneering experiment of Pasteur,12 the spontaneous deracemization and homochiral self-sorting of a racemic mixture has been a wellknown phenomenon commonly observed, suggesting the preferable intermolecular interactions and crystallinity among component molecules (low molar mass) with same configuration.13 Knowledge from this important finding has promoted many areas of synthetic chemistry, supramolecular chemistry and materials science. In some cases, however, heterochiral assembly of racemic chiral compounds could also be discovered. For example, Gao et al. published that a heterochiral metallocycle could be formed by self-discriminating of racemic binaphthyl-bisbipyridines and silver ions in solution.14 Also, Fuchter et al. reported that the racemic helically chiral molecule 1-aza[6]helicene tends to self-assemble in a heterochiral manner in the solid state.15 Chiral organic molecules have shown potential and even commercial applications as soft materials and organic optoelectronic materials decades ago. For instance, since the forming of cholesteric (chiral nematic) phase, chiral cholesterol molecule has been found extensive application in liquid crystalline display technologies.16 In recent years, chiral organic materials have attracted tremendous attention for their future device applications in organic light-emitting diodes (OLEDs) with circularly polarized (CP) electroluminescence,17−22 CP-photodiodes23 and


2

Page 3 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

sensors of chiral small molecules,24 where the aggregation properties of chiral materials could considerably affect the device performance in the thin film (TF) state. It is well-known that the aggregation properties and device performance of organic materials is not only dependent on the structure and characteristics of an isolated molecule or polymer chain, but also greatly influenced by the assembly behavior of multiple units in the solid state. Thus, the assembly manner of multiple chiral molecules in the aggregate state plays a crucial role in the specific properties and device performance of chiral organic materials. Unfortunately, studies investigating the relationship between the assembly mode of chiral molecules and their performance in the context of devices are rare so far.15,25 Axial chirality is one of fundamental chiral geometries on the molecular scale and axially chiral compounds, especially binaphthol (BINOL) derivatives have attracted a vast amount of attention in fields of asymmetric synthesis and catalysis,26−28 chiral sensor29−32 and materials science including organic soft materials33−35 and organic optoelectronics.36−40 Therefore, it is scientifically important to investigate the assembly or aggregation manner of organic small molecules containing BINOL motif in the TF state. In this paper, an interesting case of heterochiral assembly was discovered upon the racemic mixture of an axially chiral material based on BINOL motif in the TF state and it was demonstrated that in comparison with the homochiral assemblies (3-M and 3-P), the heterochiral assemblies (3-rac) exhibit superior crystallization behavior and film morphology. More importantly, the electronic mobilities for organic thin film transistors (OTFTs) based on heterochiral assemblies (e = 1.2×102 cm2 V1 s1) are nearly two orders of magnitudes higher than those (e = 1.4×104 cm2 V1 s1) of their homochiral counterparts. EXPERIMENT SECTION


3

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 24

Materials and General methods. Tetrahydrofuran was dried using sodium and freshly distilled prior to use. 141 and 2-M/2-P42 were synthesized according to the reported procedures. 1H NMR (400 MHz) and

13C

NMR (100 MHz) spectra were measured in CDCl3 and C2D2Cl4 on JOEL

NMR instruments, using tetramethylsilane as an internal standard. MALDI-TOF spectra were carried out on InoSpec 4.7 Tesla FT-MS. Elemental analyses were performed on an Elemental Vario EL III elemental analyzer. Fourier Transform-Infrared (FT-IR) spectra were determined using a Bio-Rad FTS-185 spectrometer. Thermogravimetric analysis (TGA) were carried out on a TA Q500 instruments under a dry nitrogen flow at a heating rate of 10 °C/min, heating from room temperature to 500 °C. Differential scanning calorimetry (DSC) analysis was performed on a DSC Q2000 instrument under a nitrogen atmosphere at a heating (cooling) rate of 10 °C/min. The second heating and first cooling DSC scans are recorded. Ultraviolet-Visible-Near infrared (UVVis-NIR) spectra were measured on a UH4150 Spectrophotometer and electronic circular dichroism (ECD) were measured on a Chirascan instrument, all the thin films were fabricated by spin-coating on glasses. X-ray diffraction (XRD) data were collected from an X’Pert Pro diffraction instrument. Atomic force microscope (AFM) images were recorded on a JPK AFM in tapping mode. Synthesis of 3-M. Under a nitrogen atmosphere, a mixture of 1 (150 mg, 0.12 mmol), 2-M (26 mg, 0.046 mmol), Pd(PPh3)4 (14 mg, 0.012 mmol), and K2CO3 (62 mg, 0.43 mmol) in 16 mL redistilled THF and 4 mL H2O was stirred at 95 °C for 12 h. The mixture was poured into methanol. The

precipitate

was

filtered

and

purified

by

column

chromatography,

using

dichloromethane/petroleum ether (2/1) as the eluent. Compound 3-M was obtained as black solid, with 80 mg in 64% yield. 1H NMR (400 MHz, C2D2Cl4) δ (ppm): 8.14 (s, 2H), 8.06 (d, J = 9.0 Hz, 2H), 7.45 (dd, J = 23.5, 9.0 Hz, 4H), 7.21 (d, J = 8.9 Hz, 2H), 4.12 (dd, J = 44.2, 7.3 Hz, 8H), 3.74


4

Page 5 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(s, 6H), 1.98 (d, J = 33.0 Hz, 4H), 1.15 (m, 160H), 0.77 (t, J = 8.0 Hz, 24H). FT-IR (KBr, cm1) ν: 2922.2, 2851.0, 2212.2(C≡N), 1686.4, 1641.4, 1615.7, 1588.2, 1526.3, 1478.7, 1456.5, 1418.1, 1375.0, 1336.9, 1292.3, 1254.2, 1219.7, 1100.5, 1066.5, 1037.9, 886.3, 802.3, 784.4, 727.4, 681.4, 636.3, 591.7, 490.8. MS (MALDI) m/z: 2690.5 (M+H)+. HRMS (MALDI-FT) (m/z): (M+Na)+ Calcd. for C160H212N10O10NaS8: 2712.40458; Found: 2712.40190. Anal. Calcd. For C160H212N10O10NaS8: C, 71.39; H, 7.94; N, 5.20. Found: C, 71.24; H, 7.94; N, 5.00. Synthesis of 3-P. Under a nitrogen atmosphere, a mixture of 1 (150 mg, 0.12 mmol), 2-P (26 mg, 0.046 mmol), Pd(PPh3)4 (14 mg, 0.012 mmol), and K2CO3 (62 mg, 0.43 mmol) in 16 mL redistilled THF and 4 mL H2O was stirred at 95 °C for 12 h. The mixture was poured into methanol. The

precipitate

was

filtered

and

purified

by

column

chromatography,

using

dichloromethane/petroleum ether (2/1) as the eluent. Compound 3-P was obtained as black solid, with 85 mg in 69% yield. 1H NMR (400 MHz, C2D2Cl4) δ (ppm): 8.14 (s, 2H), 8.04 (d, J = 9.0 Hz, 2H), 7.46 (dd, J = 23.5, 9.0 Hz, 4H), 7.23 (d, J = 8.9 Hz, 2H), 4.13 (dd, J = 39.7, 7.5 Hz, 8H), 3.74 (s, 6H), 1.99 (d, J = 33.0 Hz, 4H), 1.17 (m, 160H), 0.77 (t, J = 8.0 Hz, 24H). FT-IR (KBr, cm1) ν: 2922.2, 2850.9, 2212.2(C≡N), 1686.2, 1641.5, 1616.3, 1588.5, 1526.4, 1478.9, 1456.6, 1418.5, 1375.1, 1336.7, 1292.6, 1253.9, 1219.6, 1100.4, 1067.0, 1037.7, 886.0, 802.0, 784.5, 727.4, 681.2, 636.2, 591.4, 490.9. MS (MALDI) m/z: 2690.9 (M+H)+. HRMS (MALDI-FT) (m/z): (M+Na)+ Calcd. for C160H212N10O10NaS8: 2712.40458; Found: 2712.40243. Anal. Calcd. For C160H212N10O10NaS8: C, 71.39; H, 7.94; N, 5.20. Found: C, 71.31; H, 8.14; N, 4.99. Grazing incidence wide-angle X-ray scattering (GIWAXS) measurements. 2D GIWAXS measurements were performed at the small and wide angle X-ray scattering beamline at the Australian Synchrotron43. A Pilatus 1M 2-dimensional detector with 0.172 mm × 0.172 mm active


5

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 24

pixels was utilized in integration mode. The detector was positioned approximately 300 mm downstream from the sample location. The precise sample-to-detector distance was determined with a silver behenate standard. X-ray photons with 11 KeV energy were used, with 3 x 1 s exposures taken with different lateral offsets per image to fill in gaps between the detector elements. These three exposures were stitched in software. A series of images were taken as a function of angle of incidence, with the images shown taken close to the critical angle identified as the angle that produced the maximum scattering intensity. 2-dimensional raw data was reduced and analyzed with a modified version of Nika. GIWAXS patterns shown have been corrected to represent real qZ and qXY axes with consideration of missing wedge. OTFT device fabrication and measurements. The OTFT devices were fabricated as bottomgate top-contact (BGTC) structures with a channel length of 31 m and a width of 273 m. Firstly, the Si/SiO2 substrates were washed by ultrasonication in deionized water, immerged into a hot mixture of sulfuric acid (98%), and hydrogen peroxide (v/v = 2:1) for 15 min to get rid of residual organic impurities absorbed on the substrate, and then successively cleaned by ultrasonication in deionized water, isopropyl alcohol, acetone, and finally dried up with flow of purged N2. Octadecyltrichlorosilane (OTS) modification of Si/SiO2 surface was carried out for about 4 h by vapor-deposition method. Then, the substrates were washed with chloroform, n-hexane, isopropyl alcohol, and acetone by ultrasonic cleaning again. At last, the substrates were dried with flow of purged N2. The active layers were spin-coated on the top of OTS-treated SiO2 with 10 μL of their o-dichlorobenzene solution (10 mg mL1) at 3000 rpm. Au was used as source and drain electrodes, and was deposited on the top of the active layer through a shadow mask under high vacuum. The electric characteristics of the devices were measured by a Keithley 4200-SCS semiconductor analyzer in a glovebox with a nitrogen atmosphere.


6

Page 7 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

RESULTS AND DISCUSSION Synthesis and thermodynamic properties. As shown in Scheme 1, 3-M and 3-P were synthesized by Suzuki-coupling with optically active 2-M or 2-P and a naphthalene diimide (NDI) derivative 1 in yields of 64% and 69% respectively. Additionally, the racemic mixture of 3-M and 3-P in 1:1 molar ratio was dissolved in chloroform, then methanol was added dropwise to the solution to precipitate 3-rac. 3-M, 3-P and 3-rac can be dissolved in common organic solvents, such as chloroform (5 mg mL1), tetrahydrofuran (5 mg mL1) and o-dichlorobenzene (10 mg mL1). First of all, the thermal properties of 3-M, 3-P and 3-rac were studied by TGA and DSC under a nitrogen atmosphere and the data is summarized in Table 1. As shown in Figure S1, the three materials exhibit high and identical decomposition temperatures (about 400 °C for 5% weight loss), which indicates good thermal stability and meets the requirement of thermal annealing. DSC curves (Figure S1) reveal a couple of endothermic and exothermic peaks for 3-M, 3-P and 3-rac, showing similar melting points (Tm) and crystallization temperatures (Tc) at about 317 °C and 283 °C (Table 1).

O

O B O

R N

2-M

O

O B O

O

O

CN S

S NC

S

NC

R N

S

N R

O

O

O O

O

O

CN S

CN S

S S NC

O

N R

O

3-M O

R N

O

Br

S

S

CN

NC

S

S

CN

O

N R

O O

1 R= 2-decyltetradecyl

O B O

R N

2-P

O B O

CN

O S

O S NC

O

S CN

R N

S

O

O

O O

CN

O S

O

N R

O

S CN

CN S

S O

N R

3-P

Scheme 1. Synthesis routes of 3-M and 3-P.


7

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 24

Table 1. Photophysical and thermal data of 3-M, 3-P and 3-rac.

a

Compound

λmaxa (nm)

λmaxb (nm)

λmaxc (nm)

Tdd (C)

Tm/Tce (C)

3-M

640

665

807

400

317/283

3-P

640

665

807

400

317/283

3-rac

640

678

819

400

319/285

UV-Vis-NIR spectra in CH2Cl2 (105 M). b UV-Vis-NIR spectra of as-spun TFs. c New shoulder

peaks in the spectra of TFs annealed at 200 C. d Onset decomposition temperature measured by TGA under a nitrogen flow.

e

Melting temperatures (Tm) and crystallization temperatures (Tc)

determined by DSC under a nitrogen flow. Photophysical and electrochemical properties. The photophysical properties of 3-M, 3-P and 3-rac in solution and solid state were investigated by UV-Vis-NIR absorption and ECD measurements. As expected, 3-M, 3-P and 3-rac possess identical UV-Vis- NIR absorption profiles in their CH2Cl2 solutions (Figure 1) and the band at 530-800 nm can be assigned to the intramolecular charge transfer (ICT).44,45 From solution to TF (Figure 1a), the absorption bands of 3-M, 3-P and 3-rac were all red-shifted to the NIR region, suggesting the formation of J-type aggregation for three materials.46 Also, the slight shoulder peak emerging at approximately 720 nm in the as-spun TFs due to molecular aggregation increased significantly and became the main peak (Figure 1b) after thermal annealing at 200 °C. It is worth noting that 3-rac shows about 13 nm (Table 1) larger values of bathochromic shifts for max than 3-M (3-P) in as-spun film states. Additionally, a new shoulder peak that could be ascribed to stronger intermolecular aggregation emerged at around 807 nm for 3-M (3-P) and 819 nm for 3-rac (Figure 1b) after thermal annealing at 200 °C. The above differences in absorption band between 3-M (3-P) and 3-rac in the TF state


8

Page 9 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

could be reasonably attributed to the diverse assembly manner of multiple stereoisomers induced by axial chirality.47,48

Figure 1. Normalized UV-Vis-NIR spectra of 3-M, 3-P and 3-rac in a) as-spun films, and b) films thermally annealed at 200 °C with the spectrum in solution (105 M in DCM) as reference. c) ECD spectra of 3-M and 3-P in solution (105 M in DCM), as-spun films and films thermally annealed at 200 °C. ECD measurements were employed to evaluate the chiroptical responses of 3-M and 3-P. The agreement of negative (positive) Cotton effects between 2-M and 3-M (2-P and 3-P) at about 240 nm (Figure S2) indicates the configurations of axial chirality remain consistent. The ECD spectra with almost mirror-image relationship (Figure 1c) is in agreement with the converse axial chirality of 3-M and 3-P. The strong Cotton effects at long wavelength (around 650 nm) indicate that the chromophores of NDI are in an asymmetric environment because axial chirality transfers from the chiral center (BINOL) to the skeletons of NDI.25 In addition, the increase and bathochromic shift (≈ 30 nm) of ECD signal from solution to as-cast and annealed TFs suggests a specific intermolecular aggregation in the TF state. Cyclic voltammetry (CV) scans exhibit identical curves for 3-M, 3-P and 3-rac with three reversible reduction processes in dichloromethane solution (Figure S3). A LUMO level of about 4.24 eV (referenced to Fc/Fc+) is calculated from the first


9

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 24

half-wave reductive potentials (Ered11/2) at 0.18 V; with an optical band gap (1.6 eV) estimated from the absorption onset, the HOMO level is calculated to be 5.84 eV (Table S1).

Figure 2. XRD patterns of the TFs of 3-M, 3-P and 3-rac. a) as-spun TFs; b) TFs annealed at 160 °C and c) TFs annealed at 200 °C. Crystallization behavior and film morphology. X-ray diffraction and atomic force microscopy were utilized to evaluate the differences in crystallinity and film morphologies between 3-M (3-P) and 3-rac. As shown in Figure 2a, for all three materials, no diffraction peaks could be observed in XRD plots of their as-spun TFs, indicating the disordered packing of both 3M (3-P) and 3-rac without thermal annealing-induced assembly. With thermal annealing, for TFs of 3-rac, a single diffraction peak (2θ = 3.75°) appeared after thermal annealing at 160 °C (Figure 2b) and the XRD plot further showed intense and sharp Bragg reflections up to second order when annealing temperature reaching 200 °C (Figure 2c). By contrast, optically active TFs still do not exhibit obvious crystallinity even being annealed at 200 °C, implying disordered microstructures. This result indicates that the crystallinity of 3-rac is obviously better than that of 3-M (3-P) in the TF state after thermal annealing-induced assembly and also suggests heterochiral assembly of the racemic mixture of 3-M and 3-P.


10

Page 11 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 3. AFM images of as-spun TFs (a, b, c) and TFs thermally annealed at 160 °C (d, e, f) and 200 °C (g, h, i) of 3-M (a, d, g), 3-P (b, e, h) and 3-rac (c, f, i). The AFM height images of TFs of 3-M, 3-P and 3-rac in diverse annealing conditions are displayed in Figure 3. It is clear that the as-spun TFs of 3-M, 3-P and 3-rac possess similar morphologies before thermal annealing-induced assembly (Figure 3a, 3b and 3c). With the rise of annealing temperature, the grain sizes and root mean square (RMS) roughness of TFs of 3-M and 3-P increase gradually due to molecular aggregation and nucleation, but numerous grain boundaries still exist (Figure 3d, 3e, 3g and 3h). However, the racemic TFs display more uniform morphologies with smaller RMS values of about 0.6 nm and 0.7 nm after thermal annealing at 160 °C and 200 °C respectively (Figure 3f and 3i), suggesting larger grain size accompanied by less grain boundaries duo to improvement of crystallinity, which is in agreement with the XRD results.


11

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 24

To gain deep insight into the distinguishing assembly and crystallization behaviors between 3M (3-P) and 3-rac in the TF state, GIWAXS experiments were employed. As shown in Figure 4 and Figure 5, TFs of 3-M and 3-P follow almost identical trends in crystallization behavior with increasing annealing temperature. The GIWAXS patterns of 3-M and 3-P are characterized by broad isotropic rings in their 2D GIWAXS patterns, indicating randomly oriented and relatively disordered crystallites. With annealing there is an increase in crystallinity (albeit limited) as shown by the decrease in peak width and shift in the q value of Bragg reflections to lower q, see the inplane scattering profiles in Figure 5d and Figure 5e. Indexing the lowest q reflection as a lamellar stacking peak gives a lamellar stacking distance of 3-M (3-P) of 26.5 Å in as-cast films which

Figure 4. 2D GIWAXS patterns of the TFs of 3-M, 3-P and 3-rac annealed at different temperatures.


12

Page 13 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

increases to 30.0 Å in TFs annealed at 200 °C. In contrast, racemic blending of 3-M and 3-P brings a completely different trend in packing and crystallization behavior to the TFs of 3-rac with annealing temperature. As shown in Figure 4, a vast change in the 2D GIWAXS patterns can be observed for the TFs of 3-rac when annealing at 160 °C, indicating a transformation from randomly oriented to highly oriented crystallites. Moreover, with annealing at 200 °C, a series of reflections up to fifth order are observed along qZ (see also the 1D out-of-plane scattering profiles in Figure 5c) due to the regular packing of molecules along the side-chain direction indicating a high propensity of 3-M and 3-P to co-crystallize with a predominant ‘‘edge-on’’ orientation.

Figure 5. 1D GIWAXS integrated cake slices from 2D GIWAXS diffraction pattern. a)-c) Outof-plane and d)-f) In-plane GIWAXS profiles for the TFs of 3-M, 3-P and 3-rac, respectively. Spin-coated TFs: as-spun (black), annealed at 80 °C (red), annealed at 160 °C (blue) and annealed at 200 °C (green).


13

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 24

With thermal annealing, the lamellar stacking distance of 3-rac decreases from 27.9 Å in ascast film to 25.5 Å and 26.8 Å in TFs annealed at 160 °C and 200 °C respectively, which is quite different from the increased lamellar stacking distance of 3-M (3-P). Additionally, compared with their optically active counterparts, the racemic TFs annealed at 160 °C and 200 °C exhibit quite different in-plane scattering profiles (Figure 5f). The highly ordered and oriented GIWAXS images of TFs of 3-rac imply the ordered supramolecular (heterochiral) assembly of 3-M and 3-P in the racemic mixture producing a crystalline microstructure that is much more ordered than that of the homochiral assemblies. Tentatively assigning the peak with a value of qXY ≈ 0.447 Å1 to a backbone stacking reflection gives a backbone repeat distance of about 14.05 Å, and the reduction in the peak width of this peak corresponds to an increase in coherence length from 10.3 nm to 23.3 nm which illustrates the increase of crystallite size. Through the comparison above, it is unambiguous that the significantly better crystallinity and packing behavior of 3-rac is in good agreement with the uniform arrangement within crystalline layers (Figure 3f). Hence, it is reasonable to conclude that the heterochiral packing structure leading to superior crystallization behavior could be attributed to the specific intermolecular interactions between component molecules with opposite axial chirality.49 Organic thin film transistors characterization. OTFTs with BGTC structure were fabricated from 3-M, 3-P and 3-rac as active materials to probe the potential effects of manners of chiralassembly on charge transport of 3 in OTFTs. The transfer and output characteristics of OTFTs are shown in Figure 6a and Figure S4, respectively. As shown in Figure 6b and Table S2, the three materials exhibit similar electron mobilities of around 7×105 cm2 V1 s1 for as-cast devices. Interestingly, after thermal annealing at 160 °C, there was a significant rise (about 23 times) in the electron mobilities for OTFTs based on heterochiral assemblies to 1.8×103 cm2 V1 s1. In contrast,


14

Page 15 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

the devices based on homochiral TFs did not show obvious changes in performance after annealed at the same temperature (Figure 6b). With annealing temperature rising to 200 °C, while the electron mobilities of OTFTs based on heterochiral assemblies further increased to 0.012 cm2 V1 s1, only a slight improvement of electron mobility was observed for devices fabricated from homochiral TFs under the same annealing condition, with the highest mobilities of around 1.4×104 cm2 V1 s1. In addition, the current on/off ratios of OTFTs based on heterochiral assemblies also displayed one order of magnitude higher than those of devices with their homochiral counterparts after thermal annealing (Figure 6a).

Figure 6. a) The transfer characteristics of OTFTs based on TFs of 3-M, 3-P and 3-rac annealed at 200 °C. b) Average electron mobilities of OTFTs based on TFs of 3-M, 3-P and 3-rac in different annealing conditions. (The standard deviation values obtained from 18 devices for each material are represented as the error bar) CONCLUSIONS In summary, we found an interesting case of heterochiral assembly upon BINOL-based axially chiral molecules in the TF state. The photophysical, XRD and GIWAXS data provide strong evidences for the heterochiral packing of racemic mixture of 3-M and 3-P in thermally annealed


15

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 24

TFs, which is quite different with homochiral assembly of 3-M or 3-P. While homochiral assembly of 3-M or 3-P results in randomly oriented crystallites, heterochiral assembly leads to highly crystalline crystallites with a dominant ‘‘edge-on’’ orientation, which might be due to specific intermolecular interactions between 3-M and 3-P. Additionally, it can be learnt from the AFM images that heterochiral TFs display more uniform morphologies, compared with their homochiral counterparts due to the increase in crystallite size and uniform crystallite orientation. More importantly, because of distinguishing assembly manners, the heterochiral assemblies exhibit superior charge transport (approximately two orders of magnitudes) in comparison with their homochiral counterparts in OTFT. Our work contributes to an in-depth understanding of the assembly behavior of BINOL-based chiral molecules in the TF state and demonstrate superior crystallization behavior, film morphology and charge transport of heterochiral assemblies compared with their homochiral counterparts, which may open new doors for the developments of chiral sensors and novel organic soft materials. ASSOCIATED CONTENT Supporting Information. Thermal curves, ECD curves, CV measurements, Characteristics for OTFT devices, NMR, FTIR, and MS spectra. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected], *[email protected]. Notes


16

Page 17 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

The authors declare no competing financial interest. ACKNOWLEDGMENT This research was financially supported by the National Natural Science Foundation of China (21522209), the “Strategic Priority Research Program” (XDB12010100), the Shanghai Science and Technology Committee (16JC1400603), the Australian Research Council (DP170102145) and SIOC. This research was performed at the SAXS/WAXS beamline at the Australian Synchrotron, part of ANSTO. REFERENCES (1) Masamune, S.; Choy, W.; Petersen, J. S.; Sita, L. R. Double Asymmetric Synthesis and a New Strategy for Stereochemical Control in Organic Synthesis. Angew. Chem. Int. Ed. 1985, 24, 1-30. (2) Fan, Q.-H.; Li, Y.-M.; Chan, A. S. C. Recoverable Catalysts for Asymmetric Organic Synthesis. Chem. Rev. 2002, 102, 3385-3466. (3) Crawley, B. M. T. a. M. L. Asymmetric Transition-Metal-Catalyzed Allylic Alkylations: Applications in Total Synthesis. Chem. Rev. 2003, 103, 2921-2943. (4) Kyba, E. B.; Koga, K.; Sousa, L. R.; Siegel, M. G.; Cram, D. J. Chiral Recognition in Molecular Complexing. J. Am. Chem. Soc. 1973, 95, 2692-2693. (5) Tu, T.; Fang, W.; Bao, X.; Li, X.; Dotz, K. H. Visual chiral recognition through enantioselective metallogel collapsing: synthesis, characterization, and application of platinumsteroid low-molecular-mass gelators. Angew. Chem. Int. Ed. 2011, 50, 6601-6605. (6) Zhou, J.; Tang, Y. The development and application of chiral trisoxazolines in asymmetric catalysis and molecular recognition. Chem. Soc. Rev. 2005, 34, 664-676.


17

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 24

(7) Liu, M.; Zhang, L.; Wang, T. Supramolecular Chirality in Self-Assembled Systems. Chem. Rev. 2015, 115, 7304-7397. (8) Zhang, L.; Wang, T.; Shen, Z.; Liu, M. Chiral Nanoarchitectonics: Towards the Design, SelfAssembly, and Function of Nanoscale Chiral Twists and Helices. Adv. Mater. 2016, 28, 10441059. (9) Shen, Z.; Jiang, Y.; Wang, T.; Liu, M. Symmetry Breaking in the Supramolecular Gels of an Achiral Gelator Exclusively Driven by pi-pi Stacking. J. Am. Chem. Soc. 2015, 137, 16109-16115. (10) Lin, L.; Zhang, Z.; Guo, Y.; Liu, M. Fabrication of Supramolecular Chirality from Achiral Molecules at the Liquid/Liquid Interface Studied by Second Harmonic Generation. Langmuir 2018, 34, 139-146. (11) Ji, L.; Ouyang, G.; Liu, M. Binary Supramolecular Gel of Achiral Azobenzene with a Chaperone Gelator: Chirality Transfer, Tuned Morphology, and Chiroptical Property. Langmuir 2017, 33, 12419-12426. (12) Pasteur, L. Ann. Chim. Phys. 1848, 24, 442-459. (13) Rosen, B. M.; Peterca, M.; Morimitsu, K.; Dulcey, A. E.; Leowanawat, P.; Resmerita, A. M.; Imam, M. R.; Percec, V. Programming the supramolecular helical polymerization of dendritic dipeptides via the stereochemical information of the dipeptide. J. Am. Chem. Soc. 2011, 133, 51355151. (14) He, Y.; Bian, Z.; Kang, C.; Gao, L. Self-discriminating and hierarchical assembly of racemic binaphthyl-bisbipyridines and silver ions: from metallocycles to gel nanofibers. Chem. Commun. 2011, 47, 1589-1591.


18

Page 19 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(15) Yang, Y.; Rice, B.; Shi, X.; Brandt, J. R.; Correa da Costa, R.; Hedley, G. J.; Smilgies, D. M.; Frost, J. M.; Samuel, I. D. W.; Otero-de-la-Roza, A.; Johnson, E. R.; Jelfs, K. E.; Nelson, J.; Campbell, A. J.; Fuchter, M. J. Emergent Properties of an Organic Semiconductor Driven by its Molecular Chirality. ACS Nano 2017, 11, 8329-8338. (16) Reinitzer, F. Beiträge Zur Kenntniss Des Cholesterins. Monatsh. Chem. 1888, 9, 421-441. (17) Geng, Y.; Trajkovska, A.; Culligan, S. W.; Ou, J. J.; Chen, H. M. P.; Katsis, D.; Chen, S. H. Origin of Strong Chiroptical Activities in Films of Nonafluorenes with a Varying Extent of Pendant Chirality. J. Am. Chem. Soc. 2003, 125, 14032-14038. (18) Yang, Y.; da Costa, R. C.; Smilgies, D.-M.; Campbell, A. J.; Fuchter, M. J. Induction of Circularly Polarized Electroluminescence from an Achiral Light-Emitting Polymer via a Chiral Small-Molecule Dopant. Adv. Mater. 2013, 25, 2624-2628. (19) Sanchez-Carnerero, E. M.; Moreno, F.; Maroto, B. L.; Agarrabeitia, A. R.; Ortiz, M. J.; Vo, B. G.; Muller, G.; de la Moya, S. Circularly polarized luminescence by visible-light absorption in a chiral O-BODIPY dye: unprecedented design of CPL organic molecules from achiral chromophores. J. Am. Chem. Soc. 2014, 136, 3346-3349. (20) Zinna, F.; Giovanella, U.; Di Bari, L. Highly circularly polarized electroluminescence from a chiral europium complex. Adv. Mater. 2015, 27, 1791-1795. (21) Zinna, F.; Pasini, M.; Galeotti, F.; Botta, C.; Di Bari, L.; Giovanella, U. Design of LanthanideBased OLEDs with Remarkable Circularly Polarized Electroluminescence. Adv. Funct. Mater. 2017, 27, 1603719.


19

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 24

(22) Yang, D.; Han, J.; Liu, M.; Duan, P. Photon Upconverted Circularly Polarized Luminescence via Triplet-Triplet Annihilation. Adv. Mater. 2018, 30, 1805683. (23) Gilot, J.; Abbel, R.; Lakhwani, G.; Meijer, E. W.; Schenning, A. P. H. J.; Meskers, S. C. J. Polymer Photovoltaic Cells Sensitive to the Circular Polarization of Light. Adv. Mater. 2010, 22, 131-134. (24) Manoli, K.; Magliulo, M.; Torsi, L. Chiral Sensor Devices for Differentiation of Enantiomers. Top. Curr. Chem. 2013, 341, 133-176. (25) Shang, X.; Song, I.; Ohtsu, H.; Lee, Y. H.; Zhao, T.; Kojima, T.; Jung, J. H.; Kawano, M.; Oh, J. H. Supramolecular Nanostructures of Chiral Perylene Diimides with Amplified Chirality for High-Performance Chiroptical Sensing. Adv. Mater. 2017, 29, 1605828. (26) Zhou, Y.-G.; Zhang, X. Synthesis of novel BINOL-derived chiral bisphosphorus ligands and their application in catalytic asymmetric hydrogenation. Chem. Commun. 2002, 38, 1124-1125. (27) Takashi, O.; Minoru, K.; Keiji, M. Design of N-Spiro C2-Symmetric Chiral Quaternary Ammonium Bromides as Novel Chiral Phase-Transfer Catalysts: Synthesis and Application to Practical Asymmetric Synthesis of r-Amino Acids. J. Am. Chem. Soc. 2003, 125, 5139-5151. (28) Ghosh, A. K.; Mathivanan, P.; Cappiello, J. C2-Symmetric chiral bis (oxazoline)–metal complexes in catalytic asymmetric synthesis. Tetrahedron 1998, Asymmetry 9, 1-45. (29) Pu, L. Enantioselective Fluorescent Sensors: A Tale of BINOL. Acc. Chem. Res. 2012, 45, 150-163. (30) Zhao, J.; Fyles, T. M.; James, T. D. Chiral binol-bisboronic acid as fluorescence sensor for sugar acids. Angew. Chem. Int. Ed. 2004, 43, 3461-3464.


20

Page 21 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(31) Wang, M. Q.; Li, K.; Hou, J. T.; Wu, M. Y.; Huang, Z.; Yu, X. Q. BINOL-based fluorescent sensor for recognition of Cu(II) and sulfide anion in water. J. Org. Chem. 2012, 77, 8350-8354. (32) Chen, X.; Jou, M. J.; Lee, H.; Kou, S.; Lim, J.; Nam, S.-W.; Park, S.; Kim, K.-M.; Yoon, J. New fluorescent and colorimetric chemosensors bearing rhodamine and binaphthyl groups for the detection of Cu2+. Sensors Actuators B Chem. 2009, 137, 597-602. (33) Brethon, A.; Hesemann, P.; Réjaud, L.; Moreau, J. J.E.; Man, M. W. C. Functional chiral hybrid silica gels prepared from (R)- or (S)-binaphthol derivatives. J. Organomet. Chem. 2001, 627, 239-248. (34) Ma, J.; Wang, Y.; Li, X.; Yang, L.; Quan, Y.; Cheng, Y. Aggregation-induced CPL response from chiral binaphthyl-based AIE-active polymers via supramolecular self-assembled helical nanowires. Polymer 2018, 143, 184-189. (35) Makarevic, J.; Stefanic, Z.; Horvat, L.; Zinic, M. Intermolecular central to axial chirality transfer in the self-assembled biphenyl containing amino acid-oxalamide gelators. Chem. Commun. 2012, 48, 7407-7409. (36) Zheng, L.; Urian, R. C.; Liu, Y.; Jen, A. K.-Y.; Pu, L. A Binaphthyl-Based Conjugated Polymer for Light-Emitting Diodes. Chem. Mater. 2000, 12, 13-15. (37) Zhou, Y.; He, Q.; Yang, Y.; Zhong, H.; He, C.; Sang, G.; Liu, W.; Yang, C.; Bai, F.; Li, Y. Binaphthyl-Containing Green- and Red-Emitting Molecules for Solution-Processable Organic Light-Emitting Diodes. Adv. Funct. Mater. 2008, 18, 3299-3306.


21

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 24

(38) Kimoto, T.; Tajima, N.; Fujiki, M.; Imai, Y. Control of circularly polarized luminescence by using open- and closed-type binaphthyl derivatives with the same axial chirality. Chem. Asian J. 2012, 7, 2836-2841. (39) He, Q.; Lin, H.; Weng, Y.; Zhang, B.; Wang, Z.; Lei, G.; Wang, L.; Qiu, Y.; Bai, F. A HoleTransporting Material with Controllable Morphology Containing Binaphthyl and Triphenylamine Chromophores. Adv. Funct. Mater. 2006, 16, 1343-1348. (40) Wang, Y.; Li, Y.; Liu, S.; Li, F.; Zhu, C.; Li, S.; Cheng, Y. Regulating Circularly Polarized Luminescence Signals of Chiral Binaphthyl-Based Conjugated Polymers by Tuning Dihedral Angles of Binaphthyl Moieties. Macromolecules 2016, 49, 5444-5451. (41) Hu, Y.; Wang, Z.; Zhang, X.; Yang, X.; Ge, C.; Fu, L.; Gao, X. A Class of ElectronTransporting Vinylogous Tetrathiafulvalenes Constructed by the Dimerization of Core-Expanded Naphthalenediimides. Org. Lett. 2017, 19, 468-471. (42) Feng, L.; Wang, Y.; Liang, F.; Xu, M.; Wang, X. Highly selective recognition of monosaccharide based on two-component system in aqueous solution. Tetrahedron 2011, 67, 3175-3180. (43) Kirby, N. M.; Mudie, S. T.; Hawley, A. M.; Cookson, D. J.; Mertens, H. D. T.; Cowieson, N.; Samardzic-Boban, V. A low-background-intensity focusing small-angle X-ray scattering undulator beamline. J. Appl. Crystallogr. 2013, 46, 1670-1680. (44) Xiao H.; Deng Y.; Yuan J.; Gao P.; Zhao B.; Tan S. Synthesis and Photovoltaic Properties of the Copolymers Based on Carbazole with Tetrathiophene Porphyrin Side Chains Linked by a Flexible Alkyl-interval. Chin. J. Chem. 2018, 36, 599-604.


22

Page 23 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(45) Kim Y.; Hong J.; Oh J. H.; Yang C. Naphthalene Diimide Incorporated Thiophene-Free Copolymers with Acene and Heteroacene Units: Comparison of Geometric Features and ElectronDonating Strength of Co-units. Chem. Mater. 2013, 25, 3251-3259. (46) Jelley, E. E. Spectral Absorption and Fluorescence of Dyes in the Molecular State. Nature 1936, 138, 1009-1010 (47) Liu, J.; Zhang, Y.; Phan, H.; Sharenko, A.; Moonsin, P.; Walker, B.; Promarak, V.; Nguyen, T. Q. Effects of stereoisomerism on the crystallization behavior and optoelectrical properties of conjugated molecules. Adv. Mater. 2013, 25, 3645-3650. (48) He, T.; Leowanawat, P.; Burschka, C.; Stepanenko, V.; Stolte, M.; Wurthner, F. Impact of 2Ethylhexyl Stereoisomers on the Electrical Performance of Single-Crystal Field-Effect Transistors. Adv. Mater. 2018, 30, 1804032. (49) Kunitake, M.; Hattori, T.; Miyano, S.; Itaya, K. Two-Dimensional Supramolecular Arrangements of Enantiomers and Racemic Modification of 1,1-Binaphthyl-2,2-Dicarboxylic Acid. Langmuir 2005, 21, 9206-9210.


23

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 24

Table of Contents Title: From Homochiral Assembly to Heterochiral Assembly: A Leap in Charge Transport Properties of binaphthol-based axially chiral materials Authors: Ming Chen, Xuechen Jiao, Jing Li, Wenting Wu, Hanshen Xin, Christopher R. McNeill, and Xike Gao

The heterochiral assembly was observed upon a racemic binaphthol-based chiral material and the heterochiral assemblies exhibit superior charge transport than their homochiral counterparts.


24

From Homochiral Assembly to Heterochiral Assembly: A Leap in

Recommend Documents