Asymmetrically Functionalized Electron‐Deficient π‐Conjugated System for Printed Single‐Crystalline Organic Electronics

Abstract Large‐area single‐crystalline thin films of n‐type organic semiconductors (OSCs) fabricated via solution‐processed techniques are urgently demanded for high‐end electronics. However, the lack of molecular designs that concomitantly offer excellent charge‐carrier transport, solution‐processability, and chemical/thermal robustness for n‐type OSCs limits the understanding of fundamental charge‐transport properties and impedes the realization of large‐area electronics. The benzo[de]isoquinolino[1,8‐gh]quinolinetetracarboxylic diimide (BQQDI) π‐electron system with phenethyl substituents (PhC2–BQQDI) demonstrates high electron mobility and robustness but its strong aggregation results in unsatisfactory solubility and solution‐processability. In this work, an asymmetric molecular design approach is reported that harnesses the favorable charge transport of PhC2–BQQDI, while introducing alkyl chains to improve the solubility and solution‐processability. An effective synthetic strategy is developed to obtain the target asymmetric BQQDI (PhC2–BQQDI–C n ). Interestingly, linear alkyl chains of PhC2–BQQDI–C n (n = 5–7) exhibit an unusual molecular mimicry geometry with a gauche conformation and resilience to dynamic disorders. Asymmetric PhC2–BQQDI–C5 demonstrates excellent electron mobility and centimeter‐scale continuous single‐crystalline thin films, which are two orders of magnitude larger than that of PhC2–BQQDI, allowing for the investigation of electron transport anisotropy and applicable electronics.


Materials and General Characterization Methods
Reagents and anhydrous solvents were purchased from Tokyo Chemical Industry Co., Ltd and Kanto Chemicals, respectively, and o-dichlorobenzene was purified by the solvent purification system prior to use.All reactions were carried out under an atmosphere of argon.were added to a round-bottom flask under argon.The mixture was stirred at 0 °C for 2 h and the reaction was quenched by water.The compound was extracted with CH 2 Cl 2 and 2M HCl (100 mL) was added to the organic layer and the precipitates were collected via filtration.
The filtrates were dissolved in water (150 mL) and sodium carbonate was added until the white solids disappeared, and the compound was then extracted with CH 2 Cl 2 (50 mL 3).
After CH 2 Cl 2 was removed in vacuo, the title compound was obtained as a light-yellow liquid without further purification (36.1 g, 72% yield).

General synthetic procedure for one-pot synthesis of PhC 2 -BQQDI-C n .
A flame-dried Schlenk tube equipped with a stir bar was charged with compound 2 (400 mg, 1.0 equiv.),alkylamine (1.5 equiv.), and anhydrous o-DCB (0.05 M).The mixture was heated at 150 ˚C for one hour under argon and subsequently cooled to room temperature.To the dark red solution was added TfOH (2.5 equiv.)and the mixture was then stirred at 150 ˚C for three hours under argon.As the reaction completion was indicated by 1 H NMR, the mixture was added dropwise to a stirring MeOH solution and the dark precipitates were collected via vacuum filtration.The products were recrystallized from o-DCB to afford the target compounds.

Theoretical Calculations
Theoretical calculations of transfer integral and effective mass were conducted using the GAMESS package [60] .The Kohn-Sham eigenstates of all compounds in this work were calculated at the PBEPBE/6-31G(d) level of theory.Transfer integrals (t) between LUMOs of neighboring molecules in the crystal structures were estimated by the dimer method [61] .To further understand the carrier transporting capabilities in the single-crystal state, their LUMO band structures E(k) were calculated by the tight-binding approximation using transfer integrals.Intermolecular interaction energy between two adjacent molecules were obtained at the M06-2X/6-31++G(d,p) level of DFT with counterpoise correction for the basis set superposition error [62] .The calculations were performed using the Gaussian 09 program package [63] .

Electrochemical Measurements
Cyclic voltammetry was conducted on a BAS electrochemical analyzer ALS 622D using a three-electrode cell with a glassy carbon as the working electrode, a Pt wire as the counter electrode and 0.01 M Ag/AgNO 3 (in benzonitrile containing 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF 6 )) as the reference electrode.The measurements were carried out under an argon atmosphere using a benzonitrile solution at 100 ˚C with a concentration of 0.25 mM, and 0.1 M TBAPF 6 as a supporting electrolyte with a scan rate of 0.1 V s -1 .The redox potentials were calibrated with ferrocene (Fc; E(Fc/Fc + ) = 0 V) as an internal standard.
Benzonitrile was passed through a pad of aluminum oxide 60 for purification prior to use.     Figure S15.In-plane and out-of-plane thin-film XRD of PhC 2 -BQQDI-C 7 .

Molecular Dynamic Simulations
Molecular dynamics (MD) simulations of single crystal structures in this study were carried out by using the MD program GROMACS 2016.3.Since the intra-and interatomic interactions should be treated explicitly for analyzing the atomistic dynamics, an all-atom model was employed in accordance with generalized Amber force field parameters [64] .The partial atomic charges of the simulated molecules were calculated using the restrained electrostatic potential (RESP) [65] methodology, based on DFT calculations with the 6-31G(d) basis set using the GAUSSIAN 09 program [63] .
For each system, the pre-equilibration run was initially performed at the given temperature for 5 ns after the steepest descent energy minimization.All systems were subjected to preequilibration runs in the NTV ensemble before their equilibration runs.During the preequilibration runs for the NTV ensemble, the Berendsen thermostat [66] was used to maintain the temperature of the system with relaxation time of 0.2 ps and the volume of the MD cell was kept constant.Subsequently, for the NTP ensemble the equilibration run was performed using the Nosé-Hoover thermostat [67][68][69] and Parrinello-Rahman barostat [70] with relaxation times of 1.0 and 5.0 ps, respectively.For all MD simulations in the NTP ensemble, the pressure of the system was kept at 1.0 bar.The smooth particle-mesh Ewald (PME) [71] method was employed to treat the long-rang electrostatic interactions and the real space cutoff and the grid spacing are 1.2 and 0.30 nm, respectively.The time step was set to 1 fs.
To compare temperature dependence of thermal atomic fluctuations between different molecules, we calculated the B-factors related to the thermal stability as expressed below: where is the root mean square fluctuations (RMSF) of atom .The RMSF values can be estimated by using following equation: where is the time step, ( ) is the position coordinate of atom , and ̅ is the average of ( ).The RMSF values were analyzed from MD trajectories during the last 10 ns in the equilibrium.
By using the atomic coordinates at the 100 ns acquired by the MD simulation, transfer integrals t1−3 were calculated over 500 dimers at the PBEPBE/6-31G(d) level of theory.Preparations of single-crystalline thin films were carried out by the solution-processed edgecasting method [72] .Thin-film crystals of PhC 2 -BQQDI-C n were grown from 0.02-0.03wt% 1-methylnaphthalene solutions at 90-115 ˚C.After the completion of crystallization, thin films were thoroughly dried in a vacuum oven at 100 °C for 10 hours.Then, 40 nm-thick gold layers were vacuum deposited through a metal shadow mask, acting as source and drain electrodes.Objective channel regions were edged by the conventional Nd:YAG laser etching technique or manually by using cotton swabs.Before measurements, thermal annealing at 100 ˚C for 10 hours were conducted to remove residual water and improve gold electrode−semiconductor contacts.

Fabrication of Large-Area Single-Crystalline Thin Films
The single-crystalline film of PhC

Figure
Figure S16.a-c Color-coded B-factor (Å 2 ) distribution of PhC 2 -BQQDI-C n (n= 5, 6, and 7) obtained from the trajectories during the last 10 ns of a 100 ns MD simulations in the NTP ensemble and variant transfer integrals (t 1 and t 3 ) at 100 ns of the MD simulations.d-f Variant t value distributions and standard deviations () revealing the magnitude of the dynamic fluctuations.Solubility

Figure S17 .
Figure S17.Typical transfer characteristics, output curves, and gate voltage-dependent µ e of PhC 2 -BQQDI-C 5 in six different devices.

Figure S20 .
Figure S20.Shelf-life stability of single-crystalline OFETs based on PhC 2 −BQQDI−C 5 under ambient atmosphere.Transfer characteristics with a, b AL-X601 and c, d diX-SR gate dielectrics.Traces of e the normalized apparent µ and f the normalized V th .The initial µ and

Figure S21 .a
Figure S21.Thermal stress durability of single-crystalline OFETs based on PhC 2 −BQQDI−C 5 .Transfer curves of OFETs with a AL-X601 and b diX-SR gate dielectrics after annealing for 10 min at each temperature.Stress temperature dependence of the change in c µ and d V th with respect to the values at 100 °C stress.The µ and V th at 100 °C stress(µ 100°C and V th,100°C , respectively) are 1.78 cm 2 V −1 s −1 and 37.1 V for AL-X601 and 1.57 cm 2 V −1 s −1 and 9.8 V for diX-SR, respectively.W/L = 100 µm/100 µm.

Figure S24 .
Figure S24.V G dependent saturated µ e (µ sat ) of large-area single-crystalline thin film of PhC 2 -BQQDI-C 5 with their corresponding angle (˚) relative to the printing direction.

Table S1 .
Optical gap estimated from the Tauc plots.These data can be obtained free of charge at www.ccdc.cam.ac.uk/data_request/cif.The temperature-variant PXRD studies of PhC 2 -BQQDI-C 5 was carried out using the synchrotron X-ray powder diffraction with the wavelength of 0.8 Å at BL44B2 at SPring-8 Material PhC 2 −BQQDI PhC 2 −BQQDI−C 5 PhC 2 −BQQDI−C 6 PhC 2 −BQQDI−C 7 2 for all reflections [SHELXL (Ver.2014/7) or SHELXL (Ver.2018/3)].While positions of all hydrogen atoms were calculated geometrically, and refined by applying riding model, all other atoms were refined anisotropically.Crystallographic data have been deposited in the Cambridge Crystallographic Data Centre as a supplementary publication.
.6 nF cm -2 ).Similarly, C i of the SiO 2 /diX-SR gate dielectrics was measured to be 26.6 nF cm −2 .Electron mobility and threshold voltage were extracted from the transfer characteristics by using the conventional equation for the saturation regime: D is the drain current, W the channel width, μ the electron mobility, C i the gate capacitance per unit area, L the channel length, V G the gate voltage, and V th the threshold voltage.Thermal stress was applied by annealing the OFETs under vacuum for 10 min, and the measurements were performed in air.
Electrical evaluations of the TFTs were conducted on a Keithley 4200-SCS semiconductor parameter analyzer in air.For the SiO 2 /AL-X601 gate dielectrics, the gate capacitance per unit area (C i ) was estimated on metal−insulator−metal structures using the semiconductor parameter analyzer(12