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Solvent Accommodation: Functionalities Can Be Tailored Through Co-Crystallization Based on 1:1 Coronene‑F4TCNQ Charge-Transfer Complex Jing Zhang,†,‡,§ Guangfeng Liu,†,§ Yecheng Zhou,⊥ Guankui Long,§ Peiyang Gu,§ and Qichun Zhang*,§,∥ ‡
Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing University of Posts & Telecommunications, 9 Wenyuan Road, Nanjing 210023, China § School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore ⊥ School of Chemistry, The University of Melbourne, Parkville, Victoria 3010, Australia ∥ Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore S Supporting Information *
ABSTRACT: Because organic donor/acceptor blending systems play critical roles in ambipolar transistors, photovoltaics, and light-emitting transistors, it is highly desirable to precisely tailor the stacking of cocrystals toward different intrinsic structures and physical properties. Here, we demonstrated that the structure-stacking modes and electron-transport behaviors of coronene-F4TCNQ cocrystals (1:1) can be tuned through the solvent accommodation. Our results clearly show that the solvent accommodation not only enlarges the inner mixed packing (...DAD···) distances, leading to the depressed short-contact interactions including the side-by-side and face-by-face intermolecular interactions, but also switches off electron-transport behavior of coronene-F4TCNQ cocrystals (1:1) in ambient atmosphere. KEYWORDS: solvent accommodation, co-crystallization, supramolecular system, depressed short contact, electron transport
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the packing characteristics of these semiconducting cocrystals.18 Besides, different nano/microstructures with varied electronic performances can be realized through tuning the stoichiometric stacking of perylene-TCNQ cocrystals.19 Very recently, we have succeeded in switching the charge-transfer nature from p-type to n-type through molecular “doping”.20 Although recent experiments and theoretical calculations have achieved promising results, D−A charge-transfer complexes or cocrystals still face one problem, namely, how to exactly control appropriate stoichiometric stacking. Clearly, there is still lots of work left, which needs to be carried out through structure modification and characteristic tuning. Herein, we reported a solvent-accommodation method to control the molecule stacking in bicomponent semiconductors. In this research, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) was employed as an acceptor and highly symmetric molecule coronene was used as a donor (Scheme 1). The reason for such selection is as following: Coronene is a
rganic charge-transfer complexes have offered fruitful platforms to realize unique physical properties such as superconductivity,1,2 metallicity,3 photoconductivity,4 ferroelectricity,5,6 magnetoresistance,7 and ambipolar transport properties.8,9 Recently, the bicomponent system10,11 based on the charge-transfer interactions between organic acceptors (A) and donors (D) have been theoretically predicted to exhibit good charge-transport behaviors.12−15 One porphyrin-like aromatic macrocycle compound mesodiphenyl tetrathia[22]annulene[2,1,2,1] (DPTTA) has been employed as a typical donor to form ambipolar D−A complexes through simple solution-processed self-assembly.16,17 Interestingly, when diphenyl naphthalene diimide (DPNDI) was chosen as the acceptor molecule, the as-obtained complexes only exhibited an enhanced hole transport performance without effective π−π overlapping among diphenyl naphthalene diimide molecules (DPNDIs) in columns.15 These results suggest that the cocrystallization-engineering strategy could be a promising way to modify the charge transport properties of organic conjugated molecules. On the other hand, the intramolecular hydrogen bonding and the variation of substituent groups on nitrogen centers of the naphthalenetetracarboxydiimides (NDI) were also effective to rationally control the stoichiometry and © XXXX American Chemical Society
Received: November 23, 2016 Accepted: December 30, 2016 Published: December 30, 2016 A
DOI: 10.1021/acsami.6b15027 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces
for van der Waals interaction (∼3.5 Å),25 ensuring strong π−π interactions along the DA-type alternating π-column directions. The single crystals of complex 2 obtained from the chlorobenzene solution also belong to a triclinic system (P1̅ with cell data of a = 7.133(7) Å, b = 9.382(9) Å, c = 11.936(11) Å, α = 87.001(13)°, β = 82.136(13)°, γ = 87.129(13)°). Note that this type of cocrystal can be prepared from either chlorobenzene or p-xylene solution, which makes us believe that the commercially available chlorobenzene might have impurity molecules xylene (Figure S2). Unsurprisingly, the accommodated xylene molecules make the unit-cell volume (789.4 Å3) of 2 significantly bigger than that (620.7 Å3) of 1. In the crystal structure of 2, coronene and F4TCNQ alternatively pile up into a one-dimensional polymer-like structure along the a-axis direction, and in each column, they adopt the same tilt angle (Figure 1c, d). Comparing with complex 1, the tightly packing mode in complex 2 was interrupted by the inserted xylene molecules, leading to depressed short-contact interactions (side-by-side C−H···F and C−H···N hydrogen bonds) among coronene molecules or F4TCNQ molecules between surrounding columns (Figure S3). The intermolecular distance between coronene and F4TCNQ in the mixed column of cocrystal 2 is about 3.33 Å, larger than that in cocrystal 1 (Figure S4). It is well-known that the degree of charge transfer between the donor and the acceptor in one complex can be roughly calculated through the geometry of acceptor (for example F4TCNQ).22 The ratio of c/(b + d) indicated that the charge-transfer degrees were ∼0.08 for complex 1 and ∼0.2 for complex 2 (Figure S5). However, when the degree of chargetransfer increases, the interplane distance between donor and acceptor in coronene/F4TCNQ also increased, which may be attributed to the insertion of solvent molecules in the coronene/F4TCNQ system. Typically, a drop of solution (either chloroform or chlorobenzene/p-xylene) containing coronene and F4TCNQ (molar ratio 1:1, the overall concentration was ∼1 mg mL−1) was drop-cast onto SiO2/Si substrate, then the self-assembled supramolecular micro/nanorods can be seen on the substrate surface after the complete evaporation.26 As shown in Figure
Scheme 1. Chemical Structures of Coronene and F4TCNQ
fragment of graphite-like polycyclic aromatic hydrocarbon with a HOMO (highest occupied molecular orbital) energy level of −5.9 eV and displayed a poor p-type transport property,21 while F4TCNQ is a good electron acceptor (A) in donor− acceptor charge transfer complexes due to its lower energy level of LUMO (lowest unoccupied molecular orbital) and four substituted fluorine atoms, which could facilitate the intramolecular H−F bond to stabilize the geometry of as-prepared complexes.22,23 Although no charge transfer behavior was shown in UV− vis−NIR spectra (Figure S1), both solutions can form dark crystals through slow evaporation of the solvents, which confirmed the existence of charge-transfer between coronene and F4TCNQ in solid state. Surprisingly, the single-crystal analysis revealed that two single crystals have different singlecrystal structures although both samples have the same ratio (1:1) of coronene and F4TCNQ. The crystal of complex 1, obtained from chloroform, was consistent with the previously reported structure of coronene-F4TCNQ cocrystal,24 whereas the crystals of complex 2 were prepared from the chlorobenzene solution (Table S1). The complex 1 crystallizes in triclinic (P1̅) with DA-type alternating π-columns (Figure 1a, b), which is mainly due to the multiple side-by-side C−H···F and C−H···N hydrogen bonds as well as the face-to-face π−π interactions between adjacent coronene and F4TCNQ molecules. All coronene molecules in complex 1 adopt an almost coplanar structure with the peripheral rings slightly twisted away from the core benzene ring (
