Hydrogen Bond-Directed Cruciform and Stacked Packing of a Pyrrole

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Hydrogen bond-directed cruciform and stacked packing of a pyrrole–based azaphenacene. Paula Gómez, Miriam Más-Montoya, Ivan da Silva, José Pedro Ceron-Carrasco, Alberto Tárraga, and David Curiel Cryst. Growth Des., Just Accepted Manuscript • Publication Date (Web): 15 May 2017 Downloaded from http://pubs.acs.org on May 20, 2017

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Crystal Growth & Design

Hydrogen bond-directed cruciform and stacked packing of a pyrrole–based azaphenacene. Paula Gómez,† Miriam Más-Montoya,†‡ Iván da Silva,§ José Pedro Cerón-Carrasco,ǁ Alberto Tárraga† and David Curiel.*† †

Department of Organic Chemistry, Faculty of Chemistry, University of Murcia, Campus of

Espinardo, 30100-Murcia, Spain. ‡

Molecular Materials and Nanosystems, Institute for Complex Molecular Systems, Eindhoven

University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands. §

ISIS Facility, STFC Rutherford Appleton Laboratory, Chilton, Oxfordshire OX11 0QX, United

Kingdom. ǁ

Bioinformatics and High Performance Computing Group, Universidad Católica San Antonio de

Murcia (UCAM), Avda. Jerónimos, 135, 30107 Guadalupe, Murcia, Spain. KEYWORDS azaphenacene, slipped stack packing, cruciform packing, Hirshfeld surface.

Solid state packing plays a critical role in molecular materials to be applied within the area of organic electronics since the arrangement of molecules conditions the quality of the charge transport. Due to the difficulty in accurately predicting the crystal packing simply from the

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molecular structure, the design of molecules which can self-organize using strategically located functional groups becomes a useful approach to induce certain order directed by non-covalent interactions. The orientation of these interactions can be intentionally controlled from the early stage of molecular design and contribute to restrict the randomness of molecular arrangement in the solid state. Herein, we describe the synthesis and solid state characterization of a novel fused polyheteroaromatic system incorporating hydrogen bond donor and acceptor sites directly into a pentacyclic structure without disrupting its conjugation. A comparative study with an analogous system without hydrogen bond acceptor sites shows the remarkable effect of the hydrogen bonddirected assembly on the crystal packing and the benefits on the π-π intermolecular overlap, crucial for charge transport processes in organic semiconductors.

1. INTRODUCTION Conjugated systems have gained much attention throughout the last few years due to its application as organic semiconductors in the fabrication of different types of optoelectronic devices.1,2 However, the optimization of charge transport in organic solids still represents a challenge for the progress of the devices performance. Although the mechanism behind charge transport in organic solids is a matter of debate,3, 4 some examples have been reported for highly crystalline organic materials showing a band-like transport model, analogous to that established for inorganic semiconductors.5, 6 However, this cannot be certainly generalized. Conversely, the vast majority of organic semiconducting materials operate via a hopping mechanism between localized states7,

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and the charge transport is critically conditioned by the arrangement of

molecules. In this regard, molecular solids present the drawback of being inherently disordered due to the extremely weak non-covalent interactions that govern their solid state packing. Therefore, one of the main objectives in the area of organic semiconductors focuses on a better


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understanding about the way in which the π-conjugated molecules are ordered in the solid state. Subsequently, this will enable a better control, or predicting ability, of the packing of a certain compound from its molecular structure than it can be achieved nowadays.9 Accordingly, it is worth highlighting the extensive research based on polycyclic aromatic hydrocarbons, with special emphasis on those systems consisting in linearly fused benzene units which constitute the series of acenes.10 Different packing motifs have been described for these compounds whose only possible intermolecular interactions are based on face-to-face (C···C) or edge-to-face (CH···C) π-stacking. Anyhow, outstanding charge carrier mobilities have been measured for pentacene or rubrene adopting a herringbone and a slipped stack crystal packing, respectively. However, the weakness of π-interactions often results in the presence of different polymorphs with undesirable dissimilar charge transport properties. Additionally, the incorporation of heterocycles into the fused polyaromatic structure, which are grouped under the name of heteroacenes, has also proved to be a successful approach for the preparation of organic semiconductors. The family of thienoacenes, characterized by the presence of thiophene rings, has rendered excellent charge mobilities.11 Although the effect of the sulfur behind the good charge transport observed for certain thienoacenes still is a subject of debate, it is generally accepted that the size of the sulfur atom promotes some intermolecular interactions in the solid state that translate into an improved charge transport throughout the organic material.12 However, despite these unquestionable good results, the molecular solid state arrangement keeps being determined by very weak and uncontrollable face-to-face or edge-to-face π-interactions. It is in this context where another known series of heteroacenes, namely the azaphenacenes, can make a difference, due to the possibility of establishing strong NH···N hydrogen bonds which can govern the self-assembly of molecules within the crystal structure. Two main groups of


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azaphenacene systems can be distinguished: Those including six-membered rings, such as pyrazine and dihydropyrazine, in the polyaromatic system and those including five-membered rings, mainly pyrrole. Many examples of these compounds, basically belonging to the series of the so-called diaza and tetraazapentacene in the case of the former group13-15 and to the series of indolo[3,2-b]carbazole in the case of the second group,16, 17 have been reported in the literature. In some cases, high hole and/or electron mobilities have been achieved.18-22 Nevertheless, very few cases have been studied from the perspective of exploring the remarkable potential that these molecules could have as self-assembled materials. In this context, it should be mentioned that studies comparing the semiconducting behavior of epindolidione and quinacridone with that of their acene counterparts, tetracene and pentacene respectively, in thin film transistors demonstrated that intermolecular hydrogen-bonding can improve the charge mobility and/or the stability of the organic semiconductors.23, 24 Similarly, hydrogen-bonded tetraazapentacenes have also been reported.25 Herein we present the synthesis of the first example of a pyrrole-based azaphenacene with hydrogen bond donor (HBD) and acceptor (HBA) binding sites directly integrated in the neutral polyheteroaromatic fully conjugated system, namely pyrido[2,3b]pyrido[3',2':4,5]pyrrolo[3,2-g]indole, 2. Due to the higher energy of hydrogen bonding in comparison to either the π-π stacking or CH···C edge-to-face interactions, the integration of hydrogen bond donor and acceptor groups in the fused pentacyclic molecule should dominate the intermolecular assembly conditioning the subsequent crystal packing. The hydrogen bonddirected self-assembly in the solid state is studied by X-ray diffraction. Moreover, the supramolecular interactions in the crystal packing are discussed making use of the Hirshfeld surface and its corresponding 2D representation.26 These data are further complemented by the computational studies used for the assessment of the reorganization energy and the transfer


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integral, which set the basis for the charge transport processes in the reported solid state structures. With the aim of analyzing the effect of intermolecular hydrogen bond-directed selfassembly on the crystal packing we also carried out a comparative study with a rather unexplored indolocarbazole isomer, namely indolo[2,3-a]carbazole, 3 (Figure 1), whose structure is analogous to that of compound 2 but without any possibility of hydrogen bond self-assembly due to the lack of hydrogen bond acceptor sites.

Figure 1. Structures of pyrido[2,3-b]pyrido[3',2':4,5]pyrrolo[3,2-g]indole, 2 and indolo[2,3a]carbazole, 3.

2. RESULTS AND DISCUSSION The synthesis of the pyrido[2,3-b]pyrido[3',2':4,5]pyrrolo[3,2-g]indole, 2, is achieved using the two-step route depicted in Scheme 1. Initially a palladium catalyzed N-arylation was carried out between o-phenylenediamine and 2,3-dichloropyridine.27 The regioselective reactivity through the position 2 of the pyridine ring enabled the isolation of N,N’-bis(3-chloropyridin-2-yl)-1,2benzenediamine, 1, in a good yield. Subsequently, a double intramolecular coupling reaction was accomplished by adapting a reported synthetic method to produce a double photoinduced radical nucleophilic aromatic substitution.28 Compound 2 was isolated in an 85% yield. The structure of all the products was unequivocally characterized by the usual spectroscopic techniques, namely 1

H-NMR, 13C-NMR and mass spectrometry.


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Scheme 1. Synthetic route of compound 2. (i) Pd(OAc)2, (±)BINAP, tBuOK, PhMe, reflux; (ii) t

BuOK, DMSO, hν.

The thermogravimetric analysis of compound 2 revealed a high thermal stability since no significant mass loss was detected below 226ºC. Using this temperature as a reference for the Differential Scanning Calorimetry experiments, several heating and cooling cycles performed between room temperature and 250 ºC revealed no evidence of melting or crystallization phase transitions within the scanned range (Figure S5). The UV-vis spectrum showed two intense bands at 255 nm (ε ≈ 5·104 cm-1 M-1) and 335 nm (ε ≈ 4·104 cm-1 M-1) (Figure 2). Using TD-DFT calculations for the simulation of the absorption spectra enabled the determination of the electronic transitions between the states S0S6 for the band at 255 nm and S0S2 for the band at 335 nm. Additionally, a weak shoulder appeared at 374 nm. As expected, this absorption corresponded to the S0S1 transition and is mainly associated to the HOMO and LUMO frontier orbitals (Figure S6). Accordingly, the HOMOLUMO energy gap (3.18 eV) was calculated from the onset of this band (388 nm). The optical characterization of compound 2 was completed by mesuring its emission spectra. This showed a shoulder at 394 nm and a sharp band at 410 nm (Figure 2). As it is typically observed for rigid fused polyaromatic systems, a small Stokes shift (20 nm) was detected. Additionally, a low quantum yield in acetonitrile solution (Ф = 0.22) was calculated.

The absorption spectrum in

the solid state was also aquired for a thin film deposited by spin coating on a quartz substrate. Despite the significant broadening of the bands, the intermolecular interactions, reinforced in this


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case by the hydrogen bonding, produced the expected red shift in the absorption, which is more clearly manifested at longer wavelengths.

Figure 2. A) Normalized absorption (blue plot) and emission (red plot) spectra of compound 2 in THF (10-5M); B) Normalized absorption spectra of compound 2 in THF(10-5M) (blue plot) and as thin film (black dashed plot)

The electronic characterization of compound 2 was completed by electrochemical methods. In this regard, the cyclic voltammetry displayed an irreversible one-electron wave with its anodic peak potential at 1262 mV (Figure S7). The HOMO energy (-5.70 eV) could be approximated from the onset of the oxidation wave (1001 mV).29, 30 The low lying HOMO can be interpreted as interesting property of the new heterophenacene, in terms of its stability towards ambient oxidation.31 Besides, the LUMO energy (-2.52 eV) was calculated by difference from the previously determined optical HOMO-LUMO gap. Since the electronic structure of compound 2 is adequate for hole transport, with the aim of corroborating the aptitude of this novel molecule to be applied in the field of organic electronics, its crystal structure was studied by X-ray diffraction. Interestingly, the rational design of the


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pyrrole-based azaphenacene led to the desired hydrogen bond-directed self-assembly in the solid state. As it can be observed in Figure 3, the fused pentacyclic structure is flat. Additionally, each molecule is connected via hydrogen bond interactions with six surrounding molecules. Three different types of hydrogen bonds can be observed: NH···N (pink dotted line), CH···N (blue dotted line) and CH···C (orange dotted line). All these hydrogen bond interactions imply the participation of a pyridine ring, which emphasizes the relevance of that heterocycle in the novel heterophenacene system.

Figure 3. Short contacts in the X-ray structure of compound 2. (Pink) NH···N hydrogen bond interactions (simplified view A); (Blue) CH···N hydrogen bond interactions (simplified view B); (Orange) CH···C edge-to-face interactions (simplified view C).


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Using the molecule highlighted in blue in Figure 3 as a reference, it can be observed how the two pyrrole NH groups converge to interact with the pyridine nitrogen of another molecule (N···N, 3 Å) placed in an almost orthogonal plane (Figure 3A). The angle between these two planes is 85.4º. In turn, one of the pyridine nitrogen atoms in the reference molecule is hydrogen bonded by the convergent pyrrole rings from a second neighbor molecule. The CH in the mentioned pyridine ring works as hydrogen bond donor site to interact with a third neighbor molecule, through one of its pyridine nitrogen atoms (C···N, 3.4 Å) (Figure 3B). This interaction is identically established by the reference molecule accepting the hydrogen bond from the CH of a fourth neighbor molecule. Those molecules linked by CH···N hydrogen bonds form a 1D extended supramolecular structure. The 1D assembly shows short steps (1 Å) defined by the distance between the planes that contain each molecule. All the above described hydrogen bonded network reinforces a set of π-staking interactions where molecules are piled up in slightly slipped columns. These columns have two orientations and define a cruciform arrangement according to the previously mentioned 85.4º angle between the planes of the molecules interacting via NH···N hydrogen bonds. Apart from the mentioned hydrogen bond interactions, CH···π edge-to-face interactions are also observed in the solid state organization of compound 2 (C···C, 3.6-3.7 Å). As a result, a herringbone packing is adopted between adjacent π-stacked columns (Figure 3C). This molecular arrangement contrasts with the crystal structure of indolo[2,3-a]carbazole, 3 (Figure 4). The replacement of the pyridine rings by benzene rings at both ends of the molecule, thwarts any possibility of hydrogen bonding. Moreover, it is worth pointing out that, related to the above cited problem of polymorphism, two polymorphs have been reported for this molecule.32,33 Anyhow, differently from compound 2, the indolo[2,3-a]carbazole system is not


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flat. The planes of the benzene rings at both ends of the molecule form angles between 171.6º and 173.4º. What is more important, regarding the crystal packing, a clearly distorted herringbone pattern is evidenced according to a stacking sequence ABA’B’. Molecules piled in column A are twisted with respect to the molecules piled in column A’ (Figure 4B). The same twist is observed between columns B and B’. Different CH···C and NH···C edge-to-face interactions determine the crystal packing. Each molecule is in close contact with four surrounding molecules at C···C and N···C distances within a range of 3.4-3.7 Å.

Figure 4. X-ray structure of compound 3 (phase I).

Considering the structural similarity of molecules 2 and 3, but the very different supramolecular interactions governing their solid state packing, it is interesting to obtain a comparative analysis from their Hirshfeld surfaces.34 These are described as the isosurfaces where both the electron densities of an individual molecule and its environment in the crystal are considered to define the corresponding weighed functions. Therefore, Hirshfeld surfaces provide valuable information about non-covalent intermolecular interactions in the solid state, which becomes especially interesting in the case of fused polyaromatic systems.35-37


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The surface calculated for compound 2 shows (according to the normalized distance color code) four intense red spots corresponding to (NH···N) interactions established between the hydrogen bond donor sites at the pyrrole rings and the hydrogen bond acceptor sites at the pyridine ring (Figure 5). Another less intense red spot is located on the nitrogen of the pyridine located at the other end of the molecule which corresponds to the weaker hydrogen bond CH···N. Additionally, some other pale red regions can be observed on the right hand side of the surface, both on the top and on the right end of the molecule, which are ascribed to the CH···π interactions. These red surfaces confirm the dominant role that hydrogen bonding plays in the solid state packing of the novel azaphenacene as it was intended from the early stage of molecular design. It is also worth noticing how a white area is depicted at the top and the bottom sides of the π-conjugated surface of the polyheteroaromatic system depicting the “footprint” of the stacked molecules. Those white spots represent the contact resulting from π-π stacked molecules.

Figure 5. Hirshfeld surfaces of compound 2.(Left) Upper-front view; (Right) Lower-back view.

Regarding the compound 3, the interactions at a shorter distance, depicted as red regions on the Hirshfeld surfaces, are observed at the long edge, where the pyrrole NHs and an outer benzene CH converge, as well as on the π surface of the polyheteroaromatic system (Figure 6). As expected, these spots correlate to the previously discussed edge-to-face interactions. Differently from compound 2, the colored regions attributed to π-π interactions on the plane of the molecule are virtually negligible.


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Figure 6. Hirshfeld surfaces of compound 3 (phase I). (Left) Upper-front view; (Right) Lowerback view.

The representation of the distances from the Hirshfeld surface to the nearest atom inside (di) and outside (de) that surface creates a 2D plot which groups the number of interacting points according to a color code (Figure 7).38,

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The individual representation of the different

interactions enables a more detailed analysis of their contribution. As far as compound 2 is concerned, the C···C interactions mainly ascribed to π-π stacking are concentrated in a region between 1.7 Å and 2.0 Å. The greenish color in this region highlights the large number of interacting points and reinforces the importance of that face-to-face interaction in the crystal packing. Regarding the H···C interactions, these cover a larger surface in the 2D plot indicating the wider range of distances that this kind of interactions can show. It is worth mentioning that those interactions depicted at shorter distances (1.6-1.7 Å) are ascribed to the edge-to-face CH···π interactions which, along with the previously mentioned C···C interactions, define the above described herringbone packing. Nevertheless, the most significant information extracted from the 2D fingerprints comes from the two spikes observed in the H···N plot, which diagonally point at the origin of the scale, typical of hydrogen bond interactions. Those points concentrated at distances below 1.4 Å correspond to the NH···N interactions that define the packing in almost orthogonal planes. Moreover, the points concentrated between 1.4 Å and 1.6 Å are correlated to the longer CH···N hydrogen bonds which define the almost coplanar 1D


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assembly. In contrast, the 2D fingerprints of compound 3 reveal the very low significance of the contribution from the C···C interactions due to the absence of face-to-face interactions. However, the important contribution of the edge-to-face interactions that lead to the distorted herringbone packing is evidenced by the cyan area depicted in the CH···C plot. Another aspect that makes a clear difference when compound 3 is compared to 2 is the absence of short contacts with the participation of nitrogen atoms, due to the lack of strong hydrogen bonds.

Figure 7. Hirshfeld surfaces 2D fingerprints. C···C interactions; H···C interactions; H···N interactions.

It is generally accepted that the stacked arrangement of molecules in parallel planes has an important influence on the charge transport in organic solids.40-42 Accordingly, upon increasing


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the surface covered by intermolecular face-to-face interactions, as long as orbitals overlap inphase, charge mobility can improve. Nevertheless, a direct cofacial disposition is not energetically favored since it would cause electrostatic repulsion between π-regions with identical electron density. Therefore, a compromise must be reached between the maximization of the shared intermolecular surface and the minimization of electrostatic repulsion which leads to a slipped arrangement of π-conjugated molecules.43 The measurement of the pitch and roll angles determine the extent of the relative displacement between two stacked molecules according to the slipping along their long and short molecular axis, respectively.44 In this regard, despite the non-planar structure observed for indolo[2,3-a]carbazole, taking the central ring as reference, a short displacement alongside the long axis (1.0 Å) correlates to a pitch angle of 19.6º (Figure 8). Conversely, a long displacement (4.9 Å) relative to the short axis is observed which results in a wide roll angle of 58.9º. As expected from a herringbone pattern, this leaves the molecules packed in parallel planes without any possibility of having a constructive overlapping. As far as compound 2 is concerned, those molecules packed in parallel planes show short relative displacements with respect to their long (3.2 Å) and short (0.5 Å) axes leading to pitch and roll angles of 42.5º and 8.5º, respectively. Accordingly, since the lower the roll angle is, the better the intermolecular orbital overlap results, the stacked molecules show quite effective face-to-face interactions (Figure 8).


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Figure 8. Pitch and roll angles of compound 2 (left) and compound 3 (right).

Both the above described arrangement of the molecules in the solid state, as well as the rigidity of those molecules, are structural features closely correlated to the parameters described by the semi-classical Marcus charge transfer theory. The transfer integral (Vab), related to the intermolecular orbital overlap, and the reorganization energy (λ), associated to the changes in the atom coordinates between the initial and final states involved in any charge transfer process, are quantum parameters that can be used to explain charge transport in organic molecular solids.45 Our theoretical simulations predict a reorganization energy of 0.249 eV for compound 2. On the other hand, the previously discussed bidirectional π-π stacking of compound 2, reinforced by a network of intermolecular hydrogen bonds, becomes an interesting structural arrangement for charge transport. Accordingly, DFT calculations (Figure 9), based on the crystal structures, revealed that the charge transfer integrals between the stacked molecules (t1-2, t1-3) displayed a much higher value than those calculated for molecules connected through any other interaction, as a result of the better orbital overlap between molecules showing face-to-face interactions. In agreement with this, molecules showing a herringbone packing governed by C-H···C edge-toface interactions showed significantly lower transfer integrals (t1-4, t1-5), although still displayed a


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slightly more efficient orbital overlap than those pairs of molecules with an orthogonal arrangement directed by hydrogen bond interactions (t1-6, t1-7). Additionally, molecules packed in adjacent stacks (t1-8, t1-9) also showed very low transfer integrals. All these data confirm the good potential of the novel azaphenacene 2 to operate as hole transporting material, in agreement with the charge transfer parameters calculated along the stacking direction.

Figure 9. Calculated transfer integrals and hole hopping rates of compound 2.

The preferential directionality of charge transport obtained from the theoretical calculations becomes a very promising feature of compound 2 when looking at its expanded solid state packing. Figure 10 shows how molecules can π-π stack in two different directions within the crystal structure, adopting a cruciform pattern and displaying a slipped-stack with two orientations.


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Figure 10. Expanded solid state packing of compound 2.

Considering that the charge transfer process would be more favored along the stacked substructures, the crystal structure of compound 2 would admit two alternative almost orthogonal pathways, which can improve the bidirectional charge transport in electronic devices based on single crystals or crystalline thin films.

3. CONCLUSIONS In summary, a simple synthetic method has been applied to the preparation of a fused pentacyclic system with strategically located hydrogen bond donor and acceptor sites integrated in the structure of a pyrrole-based azaphenacene. This compound has been fully characterized by spectroscopic, electrochemical and thermal methods that confirmed its stability and adequacy to potentially work as a hole transporting material. The rational design of this conjugated system that can self-organize through hydrogen bond interactions has proved as a valid approach to induce a highly ordered solid state structure. X-ray diffraction studies confirmed the formation of a self-assembled framework affixed by several types of hydrogen bonds leading to a unique cruciform packing. The orthogonally assembled molecules extend the network through a


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bidirectional π-π stacking arrangement. Computational calculations demonstrate that the expanded lattice defines two preferential charge transport pathways along the stacked substructures. This represents an interesting feature to be further exploited in the area of organic electronics.

4. EXPERIMENTAL SECTION N,N-bis(3-chloropyridin-2-yl)-1,2-benzenediamine, 1: A round bottom flask is charged with (±)BINAP (0.68g, 7.5% mol) and toluene (50 mL) under nitrogen atmosphere. The mixture is heated at 90-100ºC and stirred until BINAP is completely dissolved. Then, Pd(OAc)2 (0.17 g, 5% mol) is added and the solution is stirred for 15 more minutes. A second solution is prepared in another round bottom flask where o-phenylenediamine (1.56 g, 14.7 mmol), 2,3dichloropyridine (5 g, 33.8 mmol), and potassium tert-butoxide (4.95 g, 44.1 mmol) are dissolved in toluene (20 mL). The solution of the catalyst is transferred, under inert atmosphere, to the reaction flask and the resulting mixture is heated at reflux temperature for 24h. The reaction is allowed to cool down to room temperature and extracted with water (3x40 mL). The organic phase is dried over anhydrous Na2SO4, filtered and the solvent is evaporated under reduced pressure. The resulting crude is purified by column chromatography employing dichloromethane as eluent to isolate compound 1 as a yellow solid (3.19 g, 66 %). 1

H-NMR (200 MHz, CDCl3), δ (ppm): 8.07 (dd, 2H, J=4.8, 1.6 Hz), 7.70-7.66 (m, 2H), 7.54 (dd,

2H, J=7.8,1.6 Hz), 7.40 (s, 2H), 7.24-7.20 (m, 2H), 6.67 (dd, 2H, J=7.8, 4.8 Hz). 13

C-NMR (50 MHz, CDCl3), δ (ppm): 152.2, 146.0, 136.9, 133.2, 125.2, 124.9, 116.2, 114.9.

HRMS-(m/z): (C16H13Cl2N4); Found: 331.0521 (M+H)+; Calculated: 331.0512. m. p.: 158-161 ºC.


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Pyrido[2,3-b]pyrido[3',2':4,5]pyrrolo[3,2-g]indole, 2: A photochemical reactor was loaded with DMSO (110 mL), potassium tert-butoxide (0.68 g, 4.53 mmol) and compound 1 (0.5 g, 1.51 mmol), under continuous nitrogen flow. After degassing for 10-15 minutes, the medium pressure mercury lamp was switched on and the reaction run for 2.5h. After that time, the reaction was allowed to cool down to room temperature and was poured into a saturated solution of ammonium chloride (100 mL). The resulting precipitate was filtered and washed with methanol (3x30 mL) to obtain the desired product 2 (0.23 g, 85%). 1

H-NMR (200 MHz, CDCl3), δ (ppm): 11.30 (s, 2H), 8.57 (dd, 2H, J=7.6, 1.6 Hz), 8.45 (dd, 2H,

J=4.8, 1.6 Hz), 8.02 (s, 2H), 7.27 (dd, 2H, J=8, 4.8 Hz). 13

C-NMR (50 MHz, CDCl3), δ (ppm): 151.0, 145.5, 128.3, 124.4, 118.5, 116.4, 115.6, 113.2.

HRMS-(m/z): (C16H13Cl2N4); Found: 259.0986 (M+H)+; Calculated: 259.0978. m. p.: >300 ºC.

ASSOCIATED CONTENT Supporting Information. General experimental methods, 1H-NMR and 13C-NMR spectra, TGA plot, DSC plot, TD-DFT calculations, cyclic voltammetry, Hirshfeld surfaces for compound 3 (phase II), crystal structure refinement details. CCDC no. 1535467 contains the supplementary crystallographic data for compound described in this article. This data can be obtained free of charge via http://www.ccdc.cam.ac.uk/data_request/cif


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AUTHOR INFORMATION Corresponding Author David Curiel E-mail: [email protected] Funding Sources Spanish Ministry of Economy and Competitiveness.

ACKNOWLEDGMENT Authors are grateful for the financial support from the Spanish Ministry of Economy and Competitiveness (Project CTQ2014-58875) and from Fundación Séneca–Agencia de Ciencia y Tecnología de la Región de Murcia (Project 19419/PI/14-1). Authors also acknowledge the Spanish Ministry of Science and Innovation and Consejo Superior de Investigaciones Científicas for financial support and for provision of synchrotron radiation facilities. Besides, authors would like to thank E. Salas-Colera for his assistance in using beamline BM25-SpLine at the ERSF Synchrotron in Grenoble (France). REFERENCES (1) For special issues covering recent advances in organic electronics see: J. Mater. Chem. C 2016, 7, 3665-3874; ChemPhysChem 2015, 16, 1097-1314; Polym. Sci. Ser. C 2014, 56, 1-153; Adv. Mater. 2013, 25, 1805-1954. (2) Klauk, H., Organic Electronics II. More Materials and Applications ed.; Wiley-VCH: 2012; p 420. (3) Nan, G.; Yang, X.; Wang, L.; Shuai, Z.; Zhao, Y., Nuclear tunneling effects of charge transport in rubrene, tetracene, and pentacene. Phys. Rev. B 2009, 79, (11), 115203.


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For Table of Contents Use Only

Hydrogen bond-directed cruciform and stacked packing of a pyrrole–based azaphenacene. Paula Gómez, Miriam Más-Montoya, Iván da Silva, José Pedro Cerón-Carrasco, Alberto Tárraga and David Curiel.

Synopsis: Rational design of molecules targeting their hydrogen bond-directed self-organization can be used to modulate the charge transport in molecular materials.


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Hydrogen Bond-Directed Cruciform and Stacked Packing of a Pyrrole

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