StructureâProperty Relationship in an Organic Semiconductor

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Structure-Property Relationship in an Organic Semiconductor: Insights from Energy Frameworks, Charge Density Analysis and Diode Device Kunal Kumar Jha, Yogesh Yadav, Shashi B. Srivastava, Dwaipayan Chakraborty, Priya Johari, Samarendra P. Singh, and Parthapratim Munshi Cryst. Growth Des., Just Accepted Manuscript • Publication Date (Web): 29 Mar 2019 Downloaded from http://pubs.acs.org on March 29, 2019

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Crystal Growth & Design

Structure-Property Relationship in an Organic Semiconductor: Insights from Energy Frameworks, Charge Density Analysis and Diode Device Kunal K. Jha, Yogesh Yadav, Shashi B. Srivastava, Dwaipayan Chakraborty, Priya Johari, Samarendra P. Singh and Parthapratim Munshi* A lightweight organic material, trans-4'-dimethylamino-4-nitro-α-cyanostilbene, exhibits notable charge carrier mobility (~10-4 cm2V-1s-1). The non-centrosymmetric material also displays moderate second harmonic generation activity. This is one of the rarest examples of small organic materials displaying semiconductor characteristics. The charge-transfer pathway as elucidated via high-resolution single-crystal X-ray diffraction data based ‘energy frameworks’ and ‘experimental charge density’ analyses is assessed by measuring the charge carrier mobility using the space charge limited current technique on pure single-crystal diode devices. These advanced structural analyses clearly demonstrate that charge transport in organic crystals is purely governed by its molecular packing, especially the π-π stacking geometry. The balanced ambipolar charge transport behavior makes this highly soluble and thermally stable organic crystal promising for applications in optoelectronic devices. Moreover, this report introduces the crucial role of energy frameworks and charge density analyses for fundamental understanding of structure-property relationship in organic semiconductors.

Parthapratim Munshi Chemical and Biological Crystallography Laboratory, Department of Chemistry, School of Natural Science, Shiv Nadar University, Tehsil Dadri, Uttar Pradesh- 201314, India. Phone: 0120-3819130 E-mail: [email protected] Web: http://parthapratimmunshi.weebly.com

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Structure-Property Relationship in an Organic Semiconductor: Insights from Energy Frameworks, Charge Density Analysis and Diode Device Kunal K. Jha,a Yogesh Yadav,b Shashi B. Srivastava,b Dwaipayan Chakraborty,b Priya Johari,b Samarendra P. Singhb and Parthapratim Munshi*a a

Chemical and Biological Crystallography Laboratory, Department of Chemistry, School of

Natural Science, Shiv Nadar University, Tehsil Dadri, Uttar Pradesh- 201314, India. b

Department of Physics, School of Natural Science, Shiv Nadar University, Tehsil Dadri, Uttar

Pradesh- 201314, India. E-mail: [email protected]

ABSTRACT

A lightweight organic material, trans-4'-dimethylamino-4-nitro-α-cyanostilbene, exhibits notable charge carrier mobility (~10-4 cm2V-1s-1). The non-centrosymmetric material also displays moderate second harmonic generation activity. This is one of the rarest examples of small organic materials displaying semiconductor characteristics. The charge-transfer pathway as elucidated via high-resolution single-crystal X-ray diffraction data based ‘energy frameworks’ and ‘experimental charge density’ analyses is assessed by measuring the charge carrier mobility using the space charge limited current technique on pure single-crystal diode devices. These advanced structural


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analyses clearly demonstrate that charge transport in organic crystals is purely governed by its molecular packing, especially the π-π stacking geometry. The balanced ambipolar charge transport behavior makes this highly soluble and thermally stable organic crystal promising for applications in optoelectronic devices. Moreover, this report introduces the crucial role of energy frameworks and charge density analyses for fundamental understanding of structure-property relationship in organic semiconductors.

INTRODUCTION The fundamental understanding of structure-property relationship in organic functional materials has been the prime focus of the materials researchers, in recent times.1-4 The importance of the relationship between the structure-property and charge carrier mobility has also been addressed.5 Exploration of charge-transfer (CT) phenomenon in organic molecular systems has received a great attention too.6-8 The understanding of CT phenomenon demands careful study of microscopic as well as macroscopic characteristics and charge transport properties of a material. Design of intelligent molecules by introducing flexible molecular functionality and thereby tuning their molecular packing has changed the course of charge transport properties in organic functional materials, in the recent past.1-8 Consequently, the door has opened up for some new class of applications e.g. organic light emitting diodes, organic field-effect transistors (OFET), organic solar-cells, organic photovoltaic devices etc.9,10 Efficiency of charge transport for a material is highly dependent on the molecular arrangements in its crystal lattice.1-4 Various reports evidenced that the linear 2D-brick like molecular stacking with shorter intermolecular distances improve intermolecular electronic coupling and enhances the charge carrier mobility.1,11-13 Although the reports on unipolar (n-type or p-type) semiconductors are not uncommon but lightweight organic material exhibiting ambipolar (hole and electron transport within the same material) transport


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property are limted.2,14,15 Ambipolar organic materials find immense applications in fabricating complementary metal-oxide-semiconductor (CMOS)-like logic circuits with high-frequency operations, light emitting transistors, electrically pumped laser etc.2,16,17 However, engineering such efficient materials with balanced charge carrier mobility remains a challenge.1 Organic crystals with weak intermolecular interactions localize the charge carriers spatially. Quantification of those localized charges and mapping the directionality of CT pathways are essential steps for deciphering the extent of intra- and inter-molecular electronic couplings. Organic scaffolds such as nitro stilbene with π-eˉ donor (D) and acceptor (A) substituent have been the target of several experimental and theoretical investigations for discovering second harmonic generation (SHG) materials.18-20 The energy bandgap in such D–π–A planar chromophores reduces significantly as they permit a high degree of intramolecular CT (ICT). 21 Further, they facilitate intermolecular CT, leading to the generation of good frequency conversion materials.22 Absence of a center of inversion is necessary for a material to display SHG effect. The noncentrosymmetric crystal fields enhances both CT and dipole moment.23,24 In this context, ‘energy frameworks’,25 which provides qualitative picture of 3D-topology of the predominant interactions in molecular crystals and experimental charge density analysis (ECDA)26,27 approach is expected to play a crucial role for elucidating the CT pathways in molecular crystals. At the high resolution, the deformation of the electron cloud of atoms due to chemical bonding and interactions can be highlighted via multipole modeling of electron densities.26 The topology of charge density distributions ρ(r) obtained via multipole modeling can be quantified using Bader’s quantum theory of atoms in molecules (QTAIM) approach.28 Charge density ρ(r) is a physical quantity and mathematical operations can be applied on to it to derive certain topological properties; electron densities (𝐵𝐶𝑃 (𝑟)) at the bond critical point (BCP) where ACS Paragon Plus Environment

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the first derivative of ρ(r) vanishes, the second derivative of ρ(r) called Laplacians (2𝐵𝐶𝑃 (𝑟)), the curvatures (λ1, λ2 and λ3), bond paths (Rij) and bond ellipticities (ε). This advanced tool, charge density analysis, provides both quantitative and qualitative information on interaction pathways, the possible channels for CT.29,30 Here, we report the case of trans-4'-dimethylamino-4-nitro-α-cyanostilbene (1, Scheme I), a cyano substituted nitro stilbene derivative belongs to the family of D–π–A push-pull chromophore. This highly soluble and thermally stable π-conjugated organic system is characterized as ambipolar semiconductor, which also display moderate SHG activity. Initially, the ICT characteristic of 1 is established by estimating the energy gap based on first-principles density functional theory (DFT) calculations, cyclic voltammetry (CV) experiment in its solution and UV-Vis experiment on its thin-film. Crystal structure analysis using high-resolution SCXRD data revealed the intra- and inter-molecular CT pathways in its crystal. Subsequently, the in-crystal CT pathway, as elucidated based on ‘energy frameworks’ analysis and ECDA, is assessed by measuring the charge carrier mobility using the space charge limited current (SCLC) technique on single-crystal diode devices. Further, the charge carrier mobility and SHG properties are estimated based on the first-principles DFT calculations.

Scheme I. Chemical diagram of trans-4'-dimethylamino-4-nitro-α-cyanostilbene (1)


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EXPERIMENTAL SECTION General experimental procedure All the reagents used for the synthesis of 1 were procured from Sigma-Aldrich. 1H NMR spectrum was recorded using Bruker AVHDN 400 spectrometer. HRMS analysis was performed under the following operation parameters: dry gas temperature 350 °C, dry gas (N2) ﬂow rate 10 L/min, nebulizer pressure 30 psi, Vcap 4000 and fragmentor voltage 120 V using an Agilent 6540 accurate– mass Q-TOF LC/MS (Agilent Technologies, U.S.A.). Mass spectrum was acquired in the positive ion mode by scanning from 110 to 1700 in the mass to charge ratio (m/z). The injection volume was 1μL. The ﬂow rate was set at 0.3 mL/min. The mobile phase composition used for UHPLC– QTOF MS comprised of a mixture of H2O (A) and CH3CN (B), both containing 0.1% HCO2H, with an optimized linear gradient elution as follows: 0–2 min, 1–5% B; 2–7 min, 5–15% B. Thinfilm of 1 was prepared on glass substrate using 10mg/ml solution in O-DCB solvent by spin coating. Thin-film UV-Vis spectrum was obtained on UV–VIS–NIR spectrophotometer (Shimadzu Solid-Spec-3700) in the wavelength range of 300-800 nm. The optical gap energy thus calculated using equation 1240/λonset.31 DSC measurement was carried out using Mettler Toledo DSC3 instrument under nitrogen gas atmosphere. SHG activity measurement was carried out using Spectre Physics instrument equipped with INDI LASER (Nd:Yag Laser 1064 nm) at repetition rate of 10 Hz and pulse width of 8 ns. Synthesis of trans-4'-dimethylamino-4-nitro -α-cyanostilbene (1): A mixture of 4(dimethylamino) benzaldehyde (0.50 g, 3.35 mmol) and 4-Nitrohenylacetonitrile (0.54 g, 3.35 mmol) was refluxed using piperidine as basic catalyst in ethanol at 70°C for three hours as reported earlier.32-34 Filtrate was evaporated under reduced pressure to yield dark red crude product which


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was purified by column chromatography packed with silica. The desired product was obtained as a red crystalline solid (Scheme SI). The mass spectrum was obtained by reducing –NO2 to –NH2 following a known protocol.35 Details are given in ESI (Figure S1, S2). Cyclic voltammetry (CV) experiment: Autolab PGSTAT 302 N instrument was used for cyclic voltammetry experiment in potentiostatic mode. CV experiment was performed on the solution of 1 in acetonitrile using glassy carbonyl working electrode and Pt wire as auxillary electrode. Ag/Ag+ was used as standard electrode. 0.1M solution of tetrabutylammonium phosphorus hexafluoride (TBAPF6) as electrolite was dissolved in anhydrous acetonitrile solvent along with 2mg of 1. The scan rate was fixed to 100 mV/s. The oxidation and reduction states corresponding to the HOMO and LUMO were quantified using CV experiment. Measured potentials were converted to standard calomel electrode with the energy value of -4.4 eV with respect to vacuum. Electrical HOMO and LUMO levels were calculated using empirical equations as given in equations (1) and (2) and proposed by Bredas et al.31,36 Since these measurements were performed in solutions for a small molecule the half-wave potentials E1/2 of oxidation (E1/2, ox) and reduction (E1/2, red) as obtained from Figure 1(b) were used for calculating the HOMO and LUMO energy levels, respectively. EHOMO = -e (E1/2, oxidation + 4.4)

(1)

= -e (0.76 + 4.4) = - 5.16 eV ELUMO = -e (E1/2, reduction + 4.4)

(2)

= -e (-0.86 + 4.4) = - 3.54 eV


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Crystallization: A range of HPLC grade solvent tetrahydrofuran was used for growing the crystals of 1 via slow evaporation method at room temperature (22-25°C) and also at low temperature (36°C). Experiments resulted in crystals with block and plate morphologies. High-resolution X-ray diffraction experiment and data analysis: Single-crystal X-ray diffraction experiment using Bruker APEX3 diffractometer equipped with D8 Venture IμS microfocus dual sources, PHOTON 100 CMOS detector and Oxford cryogenic system resulted in high-resolution diffraction data (d = 0.45 Å). Monochromatic Mo Kα radiation (λ=0.71073 Å) was used for the data collection at 90K. Total of 20 sets of runs with varying 2θ,  and  angles were used to cover the full sphere of the reciprocal space. The exposure time used for lower angle reflections (2θ = 37.8°) was of 20s and that of the higher angle (2θ = 60.1°) was of 50s. The  angles were scanned from 0° to -180° with in-between maximum positive angle of 153°, while the frame width () was set to 0.5° for each run. The detector distance was fixed at 40 mm. The data reductions and integrations were performed using program SAINT37 and the sorting, scaling, merging and absorption corrections were performed using program SADABS38 as implemented in the Bruker APEX-3 suite. The crystal structure was then solved using SHELXT program and refined within the XSHELL graphic interface.39 Multipole modeling and refinement protocol: Program XD40 (Revision 6.03, July 31, 2015) was used to perform multipole modeling of high-resolution X-ray diffraction data collected on the crystal of 1. The structural information as obtained from the independent atom model (IAM) refinement were imported to XD using the module XDINI. The multipole refinement based on the least square refinement method was performed using the module XDLSM. The function minimized in least squares refinement was Σw(|Fo|K|Fc|)2 for all the reflections having I/σ(I) > 3. Initially, a


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scale factor refinement was carried out using all reflections. Next, the non-H atomic positions and anisotropic thermal parameters (Uij) were refined using high-order diffraction data (sin θ/λ ≥ 0.7 Å-1). The isotropic thermal parameters for H-atoms were then refined using lower angle diffraction data (sin θ/λ ≤ 0.7 Å-1) while the H-atom bond lengths (X-H) were set to average neutron bond distance values (C-CH3 = 1.059 Å, Csp2-CH2 = 1.092 Å, Csp-CH = 1.099 Å, C(Ar)-H = 1.083 Å).41 The subsequent refinements of multipoles up to octupole (l=3) were carried out in a stepwise manner using all reflections. Total of 10 different sets of k and k’ parameters were assigned for chemically different type of non-H atoms and refined in a successive manner along with the multipoles. For H-atoms, the multipoles were expanded up to dipole (l=2) only and their k and k’ values were fixed to 1.2. Finally, a refinement was performed including all these parameters and using all reflections. At each step, the refinements were continued until the convergence (10-12) was achieved. In the absence of neutron diffraction data, the crystal geometry from the last step of the refinements was considered to estimate the Uij values for H-atoms using the web server based program SHADE2.1.42 The refinement steps as carried out above were then repeated with Uij values of H-atoms set to the estimated values. However, in this case, for the H-atoms, in order to account for the anisotropy of electron densities due to bonding, the bond directed quadrupole moment component was also allowed to refine. The module XDPROP as implemented in the package XD was used to derive one-electron properties via topological analysis of electron densities using Bader’s QTAIM approach. The BCPs between the bonded and non-bonded atoms were located using the keyword CPSEARCH within the module XDPROP. The 3D deformation density and ESP maps were plotted using MoleCool QT.43 Single-crystal semiconductor diode device fabrication: Solution-grown single-crystals of 1 with thickness of 0.051 mm and 0.021 mm were chosen for fabrication of hole-only and electron-only


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diodes, respectively, in sandwich geometry. On both sides of the crystal, metal electrodes of Copper (Cu) and Silver (Ag) were deposited using thermal evaporation to realize hole-only and electron-only diodes, respectively. The effective device area for Cu and Ag based devices were of 0.359 mm2 and 0.141 mm2, respectively. Alternatively, we fabricated hole- and electron- only devices having similar contact area using Cu and Aluminum (Al) tapes for electrical contacts, respectively. Current density-voltage (j-V) characteristics measurements: The hole-only and electron-only diodes were probed using a Cascade Microtech probe station and j-V characteristics were measured under ambient conditions using Keithley 4200-SCS semiconductor characterization system. Differential Scanning Calorimetry (DSC) experiment: Thermal stability of 1 was determined upon performing DSC experiment, which was carried out using Mettler Toledo DSC-3 instrument under nitrogen gas atmosphere. Single-crystals of 1 (3.20 mg) were kept in an Al crucible and heated up to 300°C from 25°C and then cooled down to 25°C. The ramp rate used was of 5°C/min. THEORETICAL SECTION Theoretical UV-Vis spectra and HOMO-LUMO calculations: The structure of 1 was optimized with Gaussian 0944 using its crystal geometry. The semi empirical GGA (Generalized Gradient Approximation) method, Becke’s Flexible 1997 functional were used as basis with Grimme’s dispersion correction “D3” parameter (B97D3)45,46 and 6-311G** basis set. The B97D3 method includes dispersion correction term, which is essential for the accurate estimation of energies for such conjugated system. Subsequently, a time-dependent DFT (TD-DFT) calculation was performed in the presence of o-DCB solvent. The HOMO and LUMO diagrams (Figure 1a) based on the optimized geometry at the ground state were plotted using GaussView.47


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Interaction energy calculations: Crystal geometry was used to estimate the interaction energies between the atomic pairs of the molecule via energy frameworks (using magnitude of interaction energies)25 and UNI force field (using intermolecular potentials).48 For consistency, in each case, all H- bond distances were set to 1.083 Å. While UNI force field based calculation was performed using Mercury,49 energy frameworks were constructed based on the energies (electrostatic, polarization, dispersion and exchange-repulsion) calculated using B3LYP50 hybrid-functional and 6-31G(d,p) basis set with CrystalExplorer 3.1.51 In both cases, a cluster of 14 molecules were considered around the central molecule. Similar procedure was followed in earlier studies by some of us.32,33 Energy frameworks: Energy frameworks constructed using CrystalExplorer 3.1. For this purpose, all the hydrogen bond distances were normalized to 1.083 Å in the structure. A cluster of radius 3.8 Å was generated around the central molecule and the energy calculations were performed. CrystalExplorer 3.1 was used for visualization and analysis. The tube size (scale factor) of the interaction pillars were set to 100 and threshold for energy cut-off were set to zero. Charge carrier mobility calculations Crystal Geometry: The electron-ion interactions were treated using projector-augmented-wave (PAW)52 pseudo-potentials as implemented in the Vienna Ab-Initio Simulation Package (VASP),53-55 with a plane-wave kinetic energy cutoff of 400 eV. The reciprocal space resolution for k-points generation in structure relaxation and total energy calculation was set to 0.02×2Π Å−1 with a uniform Γ− centered mesh. The convergence for energy in all calculations was set to be 10−4 eV and the structures (molecule and crystal) were relaxed until the maximum HellmannFeynman forces acting on each atom reached the value ≤ 0.01 eV/Å, upon the ionic relaxation.


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Reorganization Energy and Coupling Matrix Element: The calculations for reorganization energy and coupling matrix elements for different dimer configurations were performed using Gaussian 09. All the charged and neutral geometries were optimized and all the single point energy calculations were carried out using B3LYP hybrid functional together with the 6311+g(d,p)56 basis set. We further post processed our results, obtained from Gaussian 09 package by projecting the monomer orbitals on the dimer orbital and performed the direct calculations to get the effective value of coupling matrix elements as implemented in the calc_J package.57 NLO property calculations: Molecular gas-phase dipole moment (μ), linear polarizability (α) and static first hyperpolarizability (β) values were estimated based on crystal geometry using Gaussian 09. The calculation was performed at the B3LYP/6-31G** level of theory. The tensor components of β thus obtained were used to calculate βtotal using Equation (3). βtot = [(βxxx + βxyy + βxzz)2 + (βyyy + βyzz + βyxx)2 + (βzzz + βzxx + βzyy)2]1/2

(3)

The program CRYSTAL1458 was used to perform the single-point periodic theoretical calculations at the B3LYP/6-31G(d,p) level of theory on the crystal geometry. Grimme’s dispersion function (D2) was taken in to account for this calculation. The keywords CPKS (Couple Perturbed KohnSham) along with THIRD (energy derivatives up to the third order) and both ANDERSON and BROYDEN (for mixing of KS matrix derivatives) were used to perform the in-crystal α, β and second order nonlinear susceptibility (χ2). The parameteres as used for the convergence in an earlier study by some of us33 were also used in this case. The periodic wavefunction thus obtained upon convergence on energy (10-8) was used to calculate the in-crystal properties (α, β and χ2). A similar approach was adopted for the calculations on urea, as well.


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Results and Discussion Intramolecular charge transfer Initially, the ICT characteristic of 1 is demonstrated via spatial distributions of calculated HOMO and LUMO, which are found to be predominantly populated on the donor group –N(Me)2 and the acceptor group –NO2, respectively (Figure 1a), as expected for a D–π–A system.59 The corresponding HOMO-LUMO energy gap is estimated as 1.83 eV, which correlates well with the experimental energy gap of 1.62 eV [EHOMO (-5.16 eV) – ELUMO (-3.54 eV)] as determined via CV experiment (Fig 1b, experimental section). Further, UV-Vis spectra was recorded on its thin-film (Figure 1c). The optical energy gap thus determined as 1.63 eV (1240/λonset). The thin-film UVVis spectrum is covering a good portion of visible range (λonset = 760 nm). This suggests that 1 belongs to the “red” materials60 and may respond under UV as well as visible lights. The experimental values of EHOMO and ELUMO are determined from the CV experiment (Figure 1b). Existence of low energy gap (~1.6 eV) suggests that 1 could be a potential material for fabricating semiconductor devices.61,62

Figure 1. (a) Calculated HOMO and LUMO spatial distribution (b) Cyclic voltammogram and (c) Thin-film UV-Vis spectrum of 1.


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In-crystal intra- and inter-molecular charge transfer For the exploration of intra- and inter-molecular CT pathways in its single-crystal, we have studied X-ray crystal structure of 1 at high-resolution (d = 0.45 Å) using excellent quality single-crystals. 1 crystallizes in a non-centrosymmetric polar space group Pn and no polymorphic forms are observed during its crystallization.63,64 Crystallographic details and the refinement parameters for 1 are listed in Table 1. Due to the presence of an intramolecular interaction (C(11)-H(11)•••C(8) = 2.431 Å and C(11)-H(11)•••C(8) = 114.39°) the rotation between the rings at the two ends of the C7=C9 bond is locked and the molecule adopted a planar geometry (Figure 2a). The torsion angle about the C=C bond (C(4)-C(7)=C(9)-C(10)) is almost linear (177.60°). The angle between the planes passing through the two rings is only of 4.67°. Thus, a high conjugation is achieved in the crystal of 1. This further indicates that the 1 may experience a high CT in its crystal form and may respond under external stimuli such as electricity and light. Table 1. Crystal data at 90K and crystallographic refinement parameters CCDC

1823265

Chemical Formula

C17H15N3O2

Formula weight

293.32

Space group

Pn

a, b, c (Å)

6.7523(2), 17.0869(6), 7.0229(3)

β(°)

116.916(1)

Volume (Å3), Z

722.50(5), 2

Resolution (sin θ/λ)max (Å-1)

1.111 (d = 0.45 Å)

Measured/unique reflections

119060/16389

Completeness (%)

99.8

Redundancy

14.23 (Friedel pairs unmerged)


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IAM Refinement Reflections used [I > 2σ(I) ]

7831

R(F2), Rw(F2)

0.0298, 0.0832

Goodness of fit (S)

1.098

Δρmax, Δρmin (e Å-3)

0.59, -0.34

Multipole Refinement Reflections used [I > 3σ(I)]

7587

Nref/Nv

11.87

R(F2), Rw(F2); S

0.0243, 0.0268; 2.003

Δρmax, Δρmin (e Å-3)

0.20; -0.14


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Figure 2. (a) Thermal ellipsoid plot at 50% probability level showing the atomic numbering scheme of 1 and the presence of C(11)-H(11)•••C(8) intramolecular interaction in dotted line, (b) Bricks-like stacked packing of the molecules, viewed down the a-axis and (c) Monolayer packing showing the intermolecular C-H•••O and C-H•••N interactions, viewed down the c-axis. Interestingly, the molecules in the crystal lattice of 1 pack in a brick-like stacked arrangement (Figure 2b), which is a favorable geometry for facilitating intermolecular CT.1,2,11-13 Moreover, the antiparallel molecular layers form via head-to-tail C-H•••O interactions along the b-axis (Figure 2c and Table S1), are separated by a distance of only 3.385 Å (Figure S3). The corresponding slipped - stacking interplanar distances along the c-axis are in the range of 3.268 Å to 3.565 Å. These distances are comparable to the interlayer separation of 3.336 Å in graphite.65 Further, the molecules in the monolayers pack in a columnar fashion via trifurcated C-H•••N interactions along the a-axis (Figure 2c). Among the three C-H•••N interactions, the C(9)-H(9)•••N(2)’ is the shortest (H•••N = 2.284 Å) followed by C(5)-H(5)•••N(2)’ and C(15)-H(15)•••N(2)’ interactions, respectively (Table S1). Energy frameworks,25 a graphical representation of the strength of interactions, display that the interaction energies due to - stacking along the c-axis are the major contributors (-71.6 kJ/mol and -37.8 kJ/mol, Figure 3) to the total energy of -148.0 kJ/mol (Figure S4). The contributions that follow are from the intra-layer molecules, -21.9 kJ/mol (along the a-axis) and -19.2 kJ/mol (along the b-axis) (Table S2). Also the UNI force field48 based interaction energies indicate similar trend. In this case, the molecules along the c-axis contributed -84.5 kJ/mol and -33.0 kJ/mol to the total energy of -148.4 kJ/mol followed by the molecules along the a-axis and b-axis, respectively (Figure S5). Details of the energy calculations are given in experimental section. Further, the close intermolecular contacts in the crystal of 1 are visualized and quantified via Hirshfeld surface


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analysis,66 (Figure 4) details of which are given in ESI. Crucial role of molecular packing in regulating the charge transport properties in organic semiconductors has been highlighted in few occasions.1-4

Figure 3. CrystalExplorer based (a) energy frameworks with 100 energy scale factor and zero energy threshold, viewed down the b-axis and (b) interaction energies, showing the major contributions due to - stacking interactions.

Figure 4: (a) dnorm mapped on the Hirshfeld surface of 1 and (b) Percentage contributions to the Hirshfeld surface area for the various close intermolecular contacts. Furthermore, the details of the electron density distributions in the intra- and inter-molecular regions are quantified via multipole model based ECDA using high-resolution SCXRD data.26,27


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Details of multipole modelling are discussed in experimental section and the multipole refinement parameters are listed in Table 1. The 3D deformation density map as shown in Figure 5a clearly displays the sharp features of the atomic bond densities and the directionality of the lone pairs of oxygen and nitrogen atoms. Further, the accuracy of the multipole model is verified by examining several other descriptors and plots as given in ESI (Figure S6 – S9). Subsequently, the one-electron properties are derived using Bader’s QTAIM approach.28 The distributions of electropositive surface at the donor group (-N(Me)2) region, the electronegative surface at both the acceptor groups (-CN and –NO2) regions and at the π-conjugated core region are prominently noticed in the electrostatic potential (ESP) map (Figure S9d). The BCP search within the molecule revealed the existence of a bond path (BP) between the atoms C(8) and H(11) and the path is passing through a BCP (Figure 5b), which confirms the presence of the intramolecular interaction. Corresponding Laplacian map is given in Figure S9c and the topological parameters are listed in Table 2. The large value of 𝑩𝑪𝑷 (𝒓) = 0.11 eÅ-3 and the positive value of and 2𝑩𝑪𝑷 (𝒓) = 1.01 eÅ-5 indicate that the interaction is a strong closed shell interaction. The  value of 0.56 represents the π-bonding characteristic of the interaction. The existence of ring critical point (RCP) due to the presence of the intramolecular interaction is also shown in Figure 5b. Thus, the ICT pathway in 1 is quantified and mapped. Further, the atomic charges derived from the multipole modelling are given in Figure S10. Corresponding dipole moment is determined to be large (18.5 D), which is a clear hint of a high CT material. The intermolecular interactions as highlighted in the Figure. 2c and S4 are quantified in terms of BCPs, BPs and RCPs as shown in Figure 5b and 5c. Among the C-H•••O interactions, the one between atoms O(1) and H(16C) is quantified to have highest values of 𝑩𝑪𝑷 (𝒓) and 2𝑩𝑪𝑷 (𝒓) (almost double) and more directional ( = 0.03) than the other two (Table 2). Likewise, among the C-


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H•••N interactions, the C(9)-H(9)•••N(2)‘ interaction is the most directional followed by the interactions with H(5) and H(15) atoms, respectively. Corresponding Laplacian maps are given in Figure S11. The short ••• interactions with higher values of 𝑩𝑪𝑷 (𝒓) and 2𝑩𝑪𝑷 (𝒓) than most of the C-H…O interactions (Table 2) and the ESP map as plotted over the molecular surfaces in the intermolecular region (Figure 5d) are in accordance with the existence of low band gap in this D--A system. The ESPs highlighting the electrostatic characteristics of the other type of interactions are given in Figure S12. These quantitative and qualitative analyses, especially the ESP map, suggest that indeed the - stacking path (along the c-axis) is the dominated channels for facilitating the intermolecular CT in the crystal of 1.

Figure 5. (a) 3D static deformation density. The intramolecular C-H…N interaction is shown in dotted line. The positive (blue surfaces) and negative (red surfaces) contours are starting at ±0.05 e Å-3 and with an interval of ±0.1 e Å-3, (b) Intra- C-H•••C and inter-molecular C-H•••N and CH•••O interactions, (c) intermolecular C•••C interactions in the crystal of 1 is shown via BPs (golden lines), BCPs (red dots) and RCPs (yellow dots) along with the concerned atom labels and (d) ESP map, highlighting the ••• interactions, is drawn at the interval of ± 0.1 eÅ-3. The colored contour gradient is given in the inset.


19


Page 20 of 37

Table 2. Topological parameters of the selected intra and intermolecular interactions. d1 and d2 are the distances of BCP from H-atom and the acceptor-atom, respectively.

a



Interactions

ρ

▽2ρ

Rij

d1

d2

(D-H•••A)

(eÅ-3)

(eÅ-5)

(Å)

(Å)

(Å)

C(11)-H(11)•••C(8)

0.11

1.01

2.46

1.08

1.38

0.56

C(16)-H(16C)•••O(1)a

0.06

0.64

2.43

1.01

1.42

0.03

C(17)-H(17A)•••O(1)a

0.03

0.38

2.78

1.19

1.58

1.24

C(17)-H(17A)•••O(2)a

0.03

0.33

2.75

1.17

1.58

0.98

C(5)-H(5)•••N(2)b

0.03

0.64

2.60

1.04

1.56

1.21

C(9)-H(9)•••N(2)b

0.08

1.13

2.30

0.87

1.42

0.16

C(15)-H(15)•••N(2)b

0.01

0.41

2.78

1.10

1.68

1.61

C(1)•••C(15)c

0.04

0.40

3.64

1.76

1.88

1.00

C(3)•••C(10)c

0.04

0.47

3.35

1.68

1.67

1.62

C(8)•••C(7)c

0.05

0.51

3.28

1.61

1.68

0.26

C(10)•••C(6)c

0.05

0.48

3.45

1.71

1.74

0.40

C(11)•••C(1)c

0.04

0.42

3.55

1.78

1.77

2.55

(x,1+y, z); b (1+x, y, z); c (-1/2+x, 1-y, -1/2+z) are the symmetry coordinates.

Theoretical estimation of in-crystal charge carrier mobility For finding the potentiality of 1 as a semiconductor, we have performed first-principles DFT based calculations for estimating in-crystal charge carrier mobility. For this, first, starting from crystal geometry the structure is relaxed. The corresponding optimized lattice parameters (Table S3) found to agree well with those obtained from the SCXRD experiment (Table 1). Later, molecular


20

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reorganization energies (RE, Figure S13) and intermolecular interaction energies are calculated to estimate the charge carrier mobility using Marcus theory,67,68 which is widely applied in case of molecular crystals.6,69 Corresponding hole and electron RE thus estimated as 0.164 eV and 0.435 eV, respectively (Table S4). The pair-wise intermolecular charge couplings are calculated between the first nearest neighbours of a molecule (Figure S14). Thereby, the values of hole and electron RE and the respective coupling energies (Table S5) are used to estimate the mobility of 4.08 cm2V1 -1

s and 0.08 cm2V-1s-1 for hole and electron, respectively, suggesting an ambipolar characteristic

of 1. These values are in accordance with the molecular RE values, i.e. low RE leads to higher mobility and vice versa. Semiconductor diode device fabrication and testing Corroborating the results from the high-resolution crystal structural, interaction energies, electron density analysis and the charge carrier mobility calculations, we have fabricated semiconductor diodes for determining the hole and electron mobility of 1. For this, the charge transport properties of solution-grown single-crystals of 1 are studied using SCLC technique. Two separate diodes in a metal/1(crystal)/metal sandwich-type geometry are fabricated (Figure 6a). The metal electrodes for hole-only and electron-only devices are selected based on the EHOMO and ELUMO levels of 1 as estimated from the cyclic voltammogram (Figure 1b). Copper (Cu) with work-function of 4.65 eV 𝒆𝒙𝒑

(corresponds to 𝑬𝑯𝑶𝑴𝑶 = -5.16 eV) and Silver (Ag) with work-function of 4.26 eV (corresponds to 𝒆𝒙𝒑

𝑬𝑳𝑼𝑴𝑶 = -3.54 eV) are used as symmetrical electrodes in hole-only and electron-only diodes, respectively.


21


b)

10-1

Hole-only device

Electron-only device

10-5

j  V2

10-6

10-7

j (A/m2)

10-2

j (A/m2)

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 37

j  V2

10-3

10-4

10-8

10-5

1

10

V (Volts)

1

10

V (Volts)

Figure 6. (a) Device prototype based on the single-crystal of 1 and (b) j-V characteristics for holeonly and electron-only devices. The current density-voltage (j-V) characteristics of the hole-only and electron-only diodes are measured based on the geometry as shown in Figure 6b. The devices are tested in a vertical geometry (along the ••• stacking direction, the c-axis) as it facilitated efficient charge-transfer compared to its horizontal geometry. This is in accordance with the observations made from the structural, interaction energies and electron density point of view. The Mott-Gurney relation as given below is used to determine the charge carrier mobility.70


22

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𝟗𝜺𝝁𝑽𝟐 𝒋= 𝟖𝑳𝟑 where, j is current density, V is applied voltage, L is device thickness, μ is mobility of charge carrier and ε is permittivity of the current transporting medium. For mobility calculations, the value of ε is taken to be 2ε0 where ε0 = 8.85×10−12 F/m is the vacuum permittivity. The SCLC region in each j-V characteristic (j V2) is fitted as shown in Figure 6b. In the electron-only device, the threshold voltage for trap-filling (VTF) is clearly noticeable at ~7.5 Volts. The electron mobility thus determined as ~10-4 cm2 V-1 s-1. The hole mobility as determined form the j-V plot (Figure 6b) of the hole-only device is ~10-6 cm2 V-1 s-1. Conjugated polymers with charge carrier mobility in the range of 10-5 to 10-2 cm2V-1s-1 have been used for OFET operation.71-73 However, for both type of devices, we fabricated twenty such devices and the corresponding electron and hole mobility ranges from ~10-5 to 10-4 cm2V-1s-1 and ~10-6 to 10-4 cm2V-1s-1, respectively. However, the mobility estimated based on the DFT based calculations suggest a reverse trend. Nevertheless, both experimental and theoretical results confirm that 1 is an ambipolar organic material. In this context, it is noteworthy that often the direct comparison of experimental mobility obtained by different groups itself becomes difficult as the static and dynamic disorder, which highly depends on the experimental deposition conditions, play crucial role in charge transport mobility.74 The charge transport in 1 can be attributed not only to the - stacked molecular packing (Figure 2b) but also to the high in-crystal dipole moment and the polar crystal field. NLO properties Further, as this push-pull chromophore possesses high dipole moment (18.5 D) and crystallizes in polar space group, we explored its potentiality as an SHG material. Initially, we measured SHG


23


Page 24 of 37

activity on its crushed homogeneous powder sample using the popular Perry-Kurtz method.75 The SHG activity (Table 3) is found to be higher than urea and KDP and comparable to that of CMONS,76 a well-known SHG material with similar scaffold as 1. Later, we estimated both molecular and in-crystal SHG properties of 1 based on its crystal geometry and compared with urea and CMONS following the procedure as reported earlier by some of us.33 In the gas-phase this chromophore molecule is estimated to have much higher dipole moment (13.1 D) than urea (4.5 D) and CMONS (7.1 D), Table 4. The corresponding linear polarizability (α) and static first hyperpolarizability (β) values are estimated to be much higher than urea but comparable to CMONS. Interestingly, in its crystal form, the values of αtotal, βtotal and χ2 tensor components for 1 are found to be in between those of urea and CMONS (Table 5) and comparable to those of a similar system reported earlier.33 Table 3: SHG activity measurement on 1 and comparison with known SHG material, CMONS. Nd:Yag Laser (1064 nm), Input Energy = 1.0 mJ/ Pulse

a

Compound

Signal strength (mv)

SHG  Urea

SHG  KDP

Urea

48

1.00

2.53

KDP

19

0.39

1.00

1

53

1.10

2.79

CMONSa

76

1.58

4.00

SHG activity using a modified version of the original Kurtz and Perry design, relative to urea, is

reported to be 4 (crystals grown in THF).77 In our present study, both 1 and CMONS crystals were also grown in THF. Note: Depending on the solvents used for the crystal growth CMONS displayed activities ranging from 0.15 (in dioxane) to 300 (in ethyl acetate).


24

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Table 4: Gas-phase dipole moment (μ), linear polarizability (α) and static first hyperpolarizability (β) of 1.

Compound

Gas-phase (B3LYP/6-31G**)

(CCDC ref code)

μ (D)

α (au)

β*E-30 (esu)

Urea (UREAXX02)

4.52

25.32

0.64

1

13.08

279.34

167.85

CMONS (BANHOO01)

7.07

226.97

74.91

Table 5: In-crystal linear and nonlinear properties Compound (Space group)

αtotal (au)

Urea

In-crystal (B3LYP/6-31G**) χ2xyy χ2xyz χ2xzz (au) (au) (au) 0 -0.74 0

55.57

βtotal (esu) 0.99

χ2xxx (au) 0

χ2xxy (au) 0

χ2xxz (au) 0

1 (Pn)

277.58

20.84

-0.92

0

0.41

4.84

0

CMONS (Cc)

903.60

616.49

-2.31

0

-3.41

-3.30

0

χ2yyy (au) 0

χ2yyz (au) 0

χ2xzz (au) 0

χ2zzz (au)

0.42

0

-0.54

0

0.55

-8.97

0

-10.84

0

-32.63

0

(P 421m)

Thermal stability Furthermore, DSC experiment on the crystal form of 1 displays a sharp melting at around 248°C (Figure S15). This clearly indicates that 1 grows as a pure crystal and do not undergo phase transitions and has high thermal stability. Conclusion Our systematic investigations based on the spectroscopic and high-resolution crystallographic analyses, diode device fabrication and SHG experiments together with the theoretical calculations reveal that this small SHG active organic material has ambipolar semiconductor characteristic.


25


Page 26 of 37

Thin-film based UV-Vis spectra confirm that this ‘red’ material with low optical band gap of 1.6 eV is likely to respond under UV-vis light. The HOMO-LUMO calculations predict that 1 has low energy gap of 1.8 eV and further demonstrate its ICT characteristic. The potentiality of this material as an ambipolar semiconductor is further assessed from its low value of energy band gap (1.6 eV) as determined from CV experiment. The detailed structural analysis reveal that 1 exists as a rigid planar molecule in its solid state and thus facilitates efficient CT. While C(Ar)-H•••C intramolecular interactions and -linker are identified as the ICT pathways, the CT in the intermolecular space is dominated along the c-axis due to the favourable π-π stacking of the molecules. CT pathways in the intra- and inter-molecular regions are established and mapped based on quantitative and qualitative analyses of both electron densities and interaction energies. Interestingly, this small organic molecule crystallizes in a polar space group (Pn) and possesses a very large dipole moment of 18.5 D. The moderate SHG activity, which is comparable to an wellknown SHG material, CMONS and the promising values of the estimated SHG properties of 1 suggest that this D--A push-pull chromophore could also be a potential SHG material. Hole and electron mobility as estimated using Marcus theory and as determined based on semiconductor diode device using SCLC technique confirm that 1 is an ambipolar semiconductor. Reports on the existence of ambipolar charge carrier mobility in small organic polar crystals are rare. Moreover, the solution-grown pure single-crystal of 1 exhibits balanced (~10-4 cm2V-1s-1) ambipolar charge transport behavior, which makes this lightweight yet highly stable organic material promising for applications in optoelectronic devices. Finally, here we have introduced the role of multipole based ECDA and qualitative description of energy frameworks for fundamental understanding of charge transport pathways in organic semiconductors.


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Supplementary Information The Supporting Information is available free of charge on the ACS Publications website. The information contains the general experimental procedures for characterization of compound by NMR, HRMS, synthesis scheme, Interaction energy, Hirshfeld surface analysis details, multipole refinement details and the relevant results, computational details of charge carrier mobility calculations and DSC plot. Corresponding Author Parthapratim Munshi, E-mail: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Acknowledgements We thank Shiv Nadar University (SNU) for funding and infrastructure. We thank Raja Sen for initial help with some of the calculations. References and Notes (1) Jiang, H.; Hu, P.; Ye, J.; Li, Y.; Li, H.; Zhang, X.; Li, R.; Dong, H.; Hu, W.; Kloc, C. Field‐ Effect Devices: Molecular Crystal Engineering: Tuning Organic Semiconductor from p‐type to n‐type by Adjusting Their Substitutional Symmetry. Adv. Mater. 2017, 29, 1605053,1-10.


27


Page 28 of 37

(2) Xu, H.; Zhou, Y.; Zhou, X.; Liu, K.; Cao, L.; Ai, Y.; Fan, Z.; Zhang, H.; Molecular Packing‐ Induced Transition between Ambipolar and Unipolar Behavior in Dithiophene‐4,9‐dione‐ Containing Organic Semiconductors. Adv. Funct. Mater. 2014, 24, 2907-2915. (3) Qin, Y.; Zhang, J.; Zheng, X.; Geng, H.; Zhao, G.; Xu, W.; Hu, W.; Shuai, Z.; Zhu, D. Charge‐ Transfer Complex Crystal Based on Extended‐π‐Conjugated Acceptor and Sulfur‐Bridged Annulene: Charge‐Transfer Interaction and Remarkable High Ambipolar Transport Characteristics. Adv. Mater. 2014, 26, 4093-4099. (4) Matta, M.; Pereira, M. J.; Gali, S. M.; Thuau, D.; Olivier, Y.; Briseno, A.; Dufour, I.; Ayela, C.; Wantz, G.; Muccioli, L. Unusual Electromechanical Response in Rubrene Single Crystals. Mater. Horizons, 2018, 5, 41-50. (5) Zhang, Y.; Duan, Y.; Liu, J.; Zheng, D.; Zhang, M.; Zhao, G. Influence of the Halogenated Substituent on Charge Transfer Mobility of Aniline Tetramer and Derivatives: Remarkable Anisotropic Mobilities. J. Phys. Chem. C, 2017, 121, 17633-17640. (6) Coropceanu, V.; Cornil, J.; Da Silva Filho, D. A.; Olivier, Y.; Silbey, R.; Brédas, J. -L. Charge Transport in Organic Semiconductors. Chem. Rev. 2007, 107, 926-952. (7) Reese, C.; Bao, Z. Organic Single Crystals: Tools for the Exploration of Charge Transport Phenomena in Organic Materials. J. Mater. Chem. 2006, 16, 329-333. (8) Shuai, Z.; Geng, H.; Xu, W.; Liao, Y.; André, J. -M. From Charge Transport Parameters to Charge Mobility in Organic Semiconductors through Multiscale Simulation. Chem. Soc. Rev. 2014, 43, 2662-2679. (9) Leclerc, N.; Chávez, P.; Ibraikulov, O. A.; Heiser, T.; Lévêque, P. mpact of Backbone Fluorination on π-Conjugated Polymers in Organic Photovoltaic Devices: A Review. Polymers, 2016, 8, 11 (2-27).


28

Page 29 of 37 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


(10)

Gelinck, G.; Heremans, P.; Nomoto, K.; Anthopoulos, T. D. Organic Transistors in Optical

Displays and Microelectronic Applications. Adv. Mater. 2010, 22, 3778-3798. (11)

Hu, P.; Li, H.; Li, Y.; Jiang, H.; Kloc, C. Single-crystal Growth, Structures, Charge

Transfer and Transport Properties of Anthracene-F4TCNQ and Tetracene-F4TCNQ ChargeTransfer Compounds. CrystEngComm. 2017, 19, 618-624. (12)

Chung, H.; Diao, Y.; Polymorphism as an Emerging Design Strategy for High Performance

Organic Electronics. J. Mater. Chem. C, 2016, 4, 3915-3933. (13)

Zhu, L.; Yi, Y.; Li, Y.; Kim, E.-G.; Coropceanu, V.; Brédas, J.-L. Prediction of Remarkable

Ambipolar Charge-Transport Characteristics in Organic Mixed-Stack Charge-Transfer Crystals. J. Am. Chem. Soc. 2012, 134, 2340-2347. (14)

Xue, G.; Fan, C.; Wu, J.; Liu, S.; Liu, Y.; Chen, H.; Xin, H. L.; Li, H. Ambipolar Charge

Transport of TIPS-pentacene Single-Crystals Grown from Non-polar Solvents. Mater. Horizons. 2015, 2, 344-349. (15)

Cornil, J.; Brédas, J.-L.; Zaumseil, J.; Sirringhaus, H. Ambipolar Transport in Organic

Conjugated Materials. Adv. Mater. 2007, 19, 1791-1799. (16)

Zaumseil, J.; Sirringhaus, H. Electron and Ambipolar Transport in Organic Field-Effect

Transistors. Chem. Rev. 2007, 107, 1296-1323. (17)

Schön, J. H.; Kloc, C.; Dodabalapur, A.; Batlogg, B. An Organic Solid State Injection

Laser. Science. 2000, 289, 599-601. (18)

Seidler, T.; Stadnicka, K.; Champagne, B. Second‐order Nonlinear Optical Susceptibilities

and Refractive Indices of Organic Crystals from a Multiscale Numerical Simulation Approach. Adv. Opt. Mater. 2014, 2, 1000-1006.


29


(19)

Page 30 of 37

Nalwa, H. S.; Miyata, S. Nonlinear Optics of Organic Molecules and Polymers, CRC Press,

1996. (20)

Jayatilaka, D.; Jha, K. K.; Munshi, P. Is it Reasonable to Obtain Information on the

Polarizability and Hyperpolarizability Only from the Electron Density? Aust. J. Chem. 2018, 71, 295-306. (21)

Roquet, S.; Cravino, A.; Leriche, P.; Alévêque, O.; Frere, P.; Roncali, J.

Triphenylamine−Thienylenevinylene Hybrid Systems with Internal Charge Transfer as Donor Materials for Heterojunction Solar Cells. J. Am. Chem. Soc. 2006, 128, 3459-3466. (22)

Zhang, H.; Liao, Q.; Wang, X.; Xu, Z.; Fu, H. Self-assembled Organic Hexagonal Micro-

prisms with High Second Harmonic Generation Efficiency for Photonic Devices. Nanoscale. 2015, 7, 10186-10192. (23)

Spackman, M. A.; Munshi, P.; Jayatilaka, D. The Use of Dipole Lattice Sums to Estimate

Electric Fields and Dipole Moment Enhancement in Molecular Crystals. Chem. Phys. Lett., 2007, 443, 87-91. (24)

Spackman, M. A.; Munshi, P.; Dittrich, B. Dipole Moment Enhancement in Molecular

Crystals from X‐ray Diffraction Data. ChemPhyChem, 2007, 8, 2051-2063 and the references therein. (25)

Turner, M. J.; Grabowsky, S.; Jayatilaka, D.; Spackman, M. A. Accurate and Efficient

Model Energies for Exploring Intermolecular Interactions in Molecular Crystals. J. Phys. Chem. Lett. 2014, 5, 4249-4255. (26)

Hansen, N. K.; Coppens, P. Testing Aspherical Atom Refinements on Small-molecule Data

Sets. Acta Crystallogr. Sect. A Cryst. Physics, Diffraction, Theor. Gen. Crystallogr. 1978, 34, 909-921.


30

Page 31 of 37 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


(27)

Koritsanszky, T. S.; Coppens, P. Chemical Applications of X-ray Charge-Density

Analysis. Chem. Rev. 2001, 101, 1583-1628. (28)

Bader, R. F. W. Atoms in Molecules. Acc. Chem. Res. 1985, 18, 9-15.

(29)

Gatti, C.; Macchi, P. Modern Charge-density Analysis; Springer Science & Business

Media, 2012 (30)

Munshi, P.; Row, T. N. G. Charge density based classification of intermolecular

interactions in molecular crystals. CrystEngComm, 2005, 7, 608-611. (31)

Leonat, L.; Sbarcea, G.; Branzoi, I. V. Cyclic Voltammetry for Energy Levels Estimation

of Organic Materials. U.P.B. Sci. Bull., Series B, 2013, 75, 111-118. (32)

Jha, K. K.; Dutta, S.; Kumar, V.; Munshi, P. Isostructural polymorphs: qualitative insights

from energy frameworks. CrystEngComm 2016, 18, 8497. (33)

Jha, K. K.; Dutta, S.; Munshi, P. Concomitance, Reversibility, and Switching Ability of

Centrosymmetric and Non-Centrosymmetric Crystal Forms: Polymorphism in an Organic Nonlinear Optical Material. Cryst. Growth Des., 2018, 18, 1126. (34)

Jha, K. K.; Dutta, S.; Sar, S.; Sen, S.; Munshi P. Harnessing sun for catalyst and sensitizer

free regio- and stereo-selective [2+2] cycloaddition. Tetrahedron, 2018, 74, 7326-7334. (35)

Bellamy, F. D.; Ou, K. Selective Reduction of Aromatic Nitro Compounds with Stannous

Chloride in Non-acidic and Non-aqueous Medium. Tetrahedron Lett. 1984, 25, 839-842. (36)

Bredas, J. L.; Silbey, R.; Boudreaux, D. S.; Chance, R. R. Chain-length Dependence of

Electronic and Electrochemical Properties of Conjugated Systems: Polyacetylene, Polyphenylene, Polythiophene, and Polypyrrole. J. Am. Chem. Soc. 1983, 105, 6555-6559.


31


(37)

Page 32 of 37

Sheldrick, G. M. Phase annealing in SHELX-90: Direct Methods for Larger Structures.

Acta Crystallogr., Sect. A Found. Crystallogr. 1990, 46, 467-473. (38)

Sheldrick, G. M. SADABS, TWINABS. Madison, Wisconsin, USA 2007.

(39)

XSHELL, Graphical Interface for Crystal Structure Refinement, Bruker, Madison, WI,

1995. (40)

Volkov, A.; Macchi, P.; Farrugia, L. J.; Gatti, C.; Mallinson, P.; Richter, T.; Koritsanszky,

T. XD2006 - A Computer Program for Multipole Refinement, Topological Analysis of Charge Densities and Evaluation of Intermolecular Energies from Experimental or Theoretical Structure Factors. 2006. (41)

Allen, F. H. A Systematic Pairwise Comparison of Geometric Parameters Obtained by X-

ray and Neutron Diffraction. Acta Crystallogr. Sect. B Struct. Sci. 1986, 42, 515-522. (42)

Munshi, P.; Madsen, A. Ø.; Spackman, M. A.; Larsen, S.; Destro, R. Estimated H-atom

Anisotropic Displacement Parameters: A Comparison Between Different Methods and with Neutron Diffraction Results. Acta Cryst., 2008, A64, 465-475. (43)

Hübschle, C. B.; Dittrich, B. MoleCoolQt - A Molecule Viewer for Charge-Density

Research. J. Appl. Crystallogr. 2011, 44, 238-240. (44)

Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J.

R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda,; R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A. Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.;


32

Page 33 of 37 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


Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. GAUSSIAN 09 , Revision D.01; Gaussian, Inc.: Wallingford, CT, 2013. (45)

Grimme, S. Semiempirical GGA‐type Density Functional Constructed with a Long‐range

Dispersion Correction. J. Comp. Chem., 2006, 27, 1787-1799. (46)

Grimme, S.; Antony, J; Ehrlich, S.; Kreig, H.; A Consistent and Accurate ab

initio Parametrization of Density Functional Dispersion Correction (DFT-D) for the 94 Elements H-Pu. J. Chem. Phys., 2010, 132, 154104-154119. (47)

Dennington, R.; Keith, T.; Millam, J.; Eppinnett, K.; Hovell, W. L.; Gilliland, R.

GaussView, 2009. (48)

Gavezzotti, A. Are Crystal Structures Predictable?. Acc. Chem. Res., 1994, 27, 309-314.

(49)

Macrae, C. F.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Shields, G. P.; Taylor, R.;

Towler, M.; Streek, J. V. D. Mercury: Visualization and Analysis of Crystal Structures. J. Appl. Crystallogr. 2006, 39, 453-457. (50)

Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-energy

Formula into a Functional of the Electron Density. Phys. Rev. B 1988, 37, 785-789. (51)

Wolff, S. K.; Grimwood, D. J.; McKinnon, J. J.; Turner, M. J.; Jayatilaka, D.; Spackman,

M. A. CrystalExplorer (Version 3.1). The University of Western Australia Perth, Australia 2012. (52)

Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B, 1994, 50, 17953.


33


(53)

Page 34 of 37

Kresse, G.; Furthmuller, J. Efficient Iterative Schemes for ab initio Total-Energy

Calculations Using a Plane-Wave Basis Set. Phys. Rev. B., 1996, 54, 11169-11186. (54)

Kresse, G.; Furthmuller, J. Efficiency of ab-initio Total Energy Calculations for Metals

and Semiconductors Using a Plane-Wave Basis set. Comput. Mater. Sci., 1996, 6, 15-50. (55)

Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-Wave

Method. Phys. Rev. B. 1999, 59, 1758-1775. (56)

Hehre, W. J.; Ditchfield, R.; Pople, J. A, Self—Consistent Molecular Orbital Methods.

XII. Further Extensions of Gaussian—Type Basis Sets for Use in Molecular Orbital Studies of Organic Molecules. J. Chem. Phys. 1972, 56, 2257−2261. (57)

Brown,

J.

S.

(2018).

CATNIP

(Version

1.4).

[Software].

Available

from

https://github.com/JoshuaSBrown/QC_Tools. (58)

Dovesi, R.; Orlando, R.; Erba, A.; Zicovich-Wilson, C. M.; Civalleri, B.; Casassa, S.;

Maschio, L.; Ferrabone, M.; De La Pierre, M.; D’Arco, P.; others. CRYSTAL14: A Program for the ab initio Investigation of Crystalline Solids. Int. J. Quantum Chem. 2014, 114, 12871317. (59)

Zhang, Y.; Miao, Y.; Song, X.; Gao, Y.; Zhang, Z.; Ye, K.; Wang, Y. Single-Molecule-

based White-Light Emissive Organic Solids with Molecular-Packing-Dependent Thermally Activated Delayed Fluorescence. J. Phys. Chem. Lett. 2017, 8, 4808-4813. (60)

Chemla, D. S.; Zyss, J. Nonlinear Optical Properties of Organic Molecules and Crystals;

Materials Science and Technology Series; Academic Press Inc., 1987. (61)

Roncali, J. Molecular Engineering of the Band Gap of π‐Conjugated Systems: Facing

Technological Applications. Macromol. Rapid Commun. 2007, 28, 1761-1775.


34

Page 35 of 37 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


(62)

Roncali, J. Chem. Rev. Synthetic Principles for Bandgap Control in Linear π-Conjugated

Systems. 1997, 97, 173-206. (63)

M. Van Meerssche, A. Crucq, Bull. Soc. Chim. Belg. 1959, 68, 599-612.

(64)

B. Tinant, R. Touillaux, J. P. Declercq, M. van Meerssche, G. Leroy, J. Weiler, Bull. Soc.

Chim. Belg. 1983, 92, 403-404. Note: The quality of crystal structures reported in Refs 63 and 64 are extremely poor. (65)

Greenwood, N. N.; Earnshaw, A. Chemistry of the elements, Pergamon, (New York), 1984.

(66)

Spackman, M. A.; Jayatilaka, D. Hirshfeld Surface Analysis. CrystEngComm. 2009, 11,

19-32. (67)

Marcus, R. A. Electron Transfer Reactions in Chemistry. Theory and Experiment. Rev.

Mod. Phys. 1993, 65, 599-610. (68)

Marcus, R. A. On the Theory of Oxidation‐Reduction Reactions Involving Electron

Transfer. J. Chem. Phys. 1956, 24, 966-978. (69)

Chua, L.; Zaumseil, J.; Chang, J.; Ou, E. C. W.; Ho, P. K. H.; Sirringhaus, H.; Friend, R.

H. General Observation of n-type Field-effect Behaviour in Organic Semiconductors. Nature. 2005, 434, 194-199. (70)

Mott, N. F.; Gurney, R. W. Electronic Processes in Ionic Solids 1940.

(71)

Meijer, E. J.; Deleeuw, D. M.; Setayesh, S.; Veenendaal, E. V.; Huisman, B. H.; Blom, P.

W. M.; Hummelen, J. C.; Scherf, U.; Klapwijk, T. M. Solution-processed Ambipolar Organic Field-effect Transistors and Inverters. Nature Materials, 2003, 2, 678-682. (72)

Cicoira, F.; Santato, C. Organic Light Emitting Field Effect Transistors: Advances and

Perspectives. Adv. Funct. Mater. 2007, 17, 3421-3434.


35


(73)

Page 36 of 37

Yang, X.; Li, Q.; Shuai, Z. Theoretical Modelling of Carrier Transports in Molecular

Semiconductors: Molecular Design of Triphenylamine Dimer Systems. Nanotechnology. 2007, 18, 424029(1-6) (74)

Coropceanu, V.; Cornil, J.; A. da Silva Filho, D; Olivier, Y; Silbey, R. and Bre´das, J.-L.

Charge Transport in Organic Semiconductors. Chem. Rev. 2007, 107, 926-952. (75)

Kurtz, S. K.; Perry, T. T. A Powder Technique for the Evaluation of Nonlinear Optical

Materials. J. Appl. Phys. 1968, 39, 3798-3813. (76)

Wang, Y.; Tam, W.; Stevensen, S. H.; Clement, R. A.; Calabrese, J. New Organic Non-

liner Optical Materials of stilbene and Diphenylacetylene Derivatives. Chem Phys Lett. 1988, 148, 136-141. (77)

Vrcelj, R. M.; Shepherd, E. E. A.; Yoon, C. S.; Sherwood, J. N.; Kennedy, A. R.

Preparation and Structural Evaluation of the Conformational Polymorphs of α-[(4Methoxyphenyl)methylene]-4-nitrobenzeneacetonitrile. Cryst. Growth Des. 2002, 2, 609-617.


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For Table of Contents Use Only

Structure-property relationship in one of the rare examples of lightweight organic material with ambipolar semiconductor characteristic is reported here. New insights to the relationship is given from the energy frameworks and charge density analyses point of view. Encouraging second harmonic generation properties and balanced hole and electron mobility (~10-4 cm2/Vs) make this material promising for applications in organic electronics.


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StructureâProperty Relationship in an Organic Semiconductor

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