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P-Containing Polycyclic Aromatic Hydrocarbons Rózsa Szűcs, Pierre-Antoine Bouit, Laszlo Nyulászi, Muriel Hissler

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P-Containing Polycyclic Aromatic Hydrocarbons Rózsa Szűcs, Pierre-Antoine Bouit, Laszlo Nyulászi, Muriel Hissler P-containing Polycyclic Aromatic Hydrocarbons Rózsa Szűcs, Pierre-Antoine Bouit, Laszlo Nyulászi, Muriel Hissler To cite this version: Rózsa Szűcs, Pierre-Antoine Bouit, Laszlo Nyulászi, Muriel Hissler. P-containing Polycyclic Aromatic Hydrocarbons. ChemPhysChem, Wiley-VCH Verlag, 2017, 18 (19), pp.2618-2630. 10.1002/cphc.201700438. hal-01538723 HAL Id: hal-01538723 https://hal.archives-ouvertes.fr/hal-01538723 Submitted on 14 Jun 2017 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. P-containing Polycyclic Aromatic Hydrocarbons Rózsa Szűcs,[a,b] Pierre-Antoine Bouit,*,[a] László Nyulászi,*,[b] Muriel Hissler*,[a] aromatic synthons using simple organic reactions (C-C cross- coupling, oxidations…). This method cannot be used to prepare micrometric graphene fragments, but it allows the preparation of well-defined molecules up to 10 nm (NGs or Graphene Abstract: Polycyclic Aromatic Hydrocarbons (PAHs) are highly NanoRibbons (GNRs)). In this field, pioneering work was appealing functional materials in the field of molecular performed by the group of K. Müllen during the 1990’s. They electronics. In particular, molecular engineering of these showed that with suitable polyaromatic precursors, the Scholl derivatives using organic chemistry is a powerful method to tune reaction can be used to “graphenize” large polyaromatic their properties from the point of view of the bandgap and frameworks.[ 5 ] They thus synthesized defect-free and soluble supramolecular assemblies. Another way to achieve such molecular graphenes ranging from the prototype hexa-peri- control is to take advantage of the specific reactivity of benzocoronene to GNRs up to 100 - 200 kg.mol-1 (1 and 2, 2 heteroatoms placed within the C-sp framework. This strategy Figure 1).[6] A precise structure-property study on the effect of has been successfully applied to N, S or B atoms. In this review, cycle number and size, shape (disc shape vs ribbons), edge we will detail the examples of P-containing PAHs and the effect structure (zig-zag, bay, cove, fjord…), can be properly of the P-environment on their electronic properties from both performed as the compounds are monodisperse.[7] Furthermore, experimental and theoretical points of view. the efficient hole transport properties of these compounds make them particularly appealing for these applications such as field- effect transistors and organic solar cells.[5] 1. Introduction The isolation of graphene by the Nobel Prize winners Geim and Novoselov opened new perspectives in the field of molecular materials. Its two-dimensional monolayer of sp2 carbon atoms confers to graphene exceptional electronic, thermal and mechanical properties that make it one of the most promising classes of carbon-based materials for various applications ranging from optoelectronics to energy storage.[1,2] Given its large range of applications, the synthesis of graphene- based materials is a rapidly expanding research field. Since its first isolation numerous research groups tried to find more [1,2] reproducible and efficient synthetic methods. In this context, Figure 1. Examples of reported PAHs (upper part) and heteroatom-containing [3] two main synthetic strategies emerged. The first one, based on PAHs (lower part). graphite exfoliation or oxidation, is referred to as “top-down” approach. One of its main advantages is that scaling up the Over the last ten years, another strategy emerged for the gap quantities is possible. However, structural defects, which may tuning of PAHs consisting in the introduction of heteroatoms into appear during growth or processing, are difficult to avoid and the polycyclic backbone. [ 8 , 9 , 10 ] Even though some polycyclic can deteriorate the performance of graphene-based devices.[4] heteroaromatic molecules are known since the beginning of the Even though these results are highly important, a precise control 20th century,[8] pioneering work in this area has been achieved of the structure and therefore the properties is not yet possible. by Draper et al.. [11] Hence, their N-doped benzocoronene (3, The second approach takes advantage of the possibility to Figure 1), also referred to as N-heterosuperbenzene) clearly perform a molecular engineering of the polycyclic aromatic reflects the strategy of inserting N atoms inside a hexa-peri- hydrocarbons (PAHs) by using the power of benzocoronene scaffold. The authors used the basicity and the organic/organometallic synthesis to overcome these problems. coordination ability of the pyrimidine moiety to tune the optical This stepwise “total synthesis” of molecular graphene fragments properties of the molecular graphene. Other N-containing PAHs is referred as to as the “bottom-up approach”. Indeed PAHs including extended porphyrins have also been prepared.[ 12 ] (such as hexa-peri-benzocoronene (HBC) 1, Figure 1) or Following this work, S-doped molecular graphenes were nanographenes (NGs) are prepared by connecting small synthesized.[13] Such compounds were recently used as active layer in organic or hybrid solar cells, taking advantage of the charge transport properties of both the PAH backbone and the [14] [a] R. Szűcs, P.-A. Bouit, M. Hissler thienyl rings (4, Figure 1). O-doped PAH (namely O-doped Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS - benzorylenes, 5) were also prepared by Bonifazi et al.[ 15 ] Université de Rennes 1 Recently, a new step was reached with the insertion of highly Campus de Beaulieu, 35042 Rennes Cedex France reactive B atom into these PAH structures. B-doped PAHs (6, [16] [b] R. Szűcs, L. Nyulászi Figure 1) were reported by the groups of S. Yamaguchi and M. Department of Inorganic and Analytical Chemistry, Wagner[17]. These electron-deficient molecular graphenes can Budapest University of Technology and Economics, react with anions and display tuneable properties, demonstrating Szt. Gellert ter 4 H-1111 Budapest, Hungary the power of the heteroatomic approach. Finally, significant interactions in conjugated π-systems, resulting in polyheteroatom-containing PAH such as NS,[18] BN,[19] and BO[20] significant stabilization energies.[33] have also been prepared. The case of BN - PAH is particularly We and others showed that chemical modifications and interesting as the B-N bond is isoelectronic with the C-C bond coordination to transition metals of a 3,3-P center[ 34 ] is a and boron nitride itself is a promising “graphene like” 2D- powerful method to develop new functional -conjugated material.[ 21 ] These different examples show that the chemists molecules.[ 35 ] Their HOMO and LUMO are thus precisely have been able to develop synthetic methods for the insertion of tuneable and they are chemically and thermally stable enough to heteroatoms into PAH structures having different Lewis and be inserted in OLEDs or solar cells.[36] The high reactivity of the nucleophilic characters leading to specific physical properties. P-atom toward organic reagents and transition metals offers an Effectively, a crucial point in this field is the need to adapt the almost unlimited way of tuning the properties of synthetic approaches developed for the “classical” PAHs to the organophosphorus derivatives.[37] Furthermore, the diversity of specific reactivity of the heteroatoms. Generally speaking, the conjugated P-heterocycles (3-membered phosphirene[ 38 ] 4- preparation of such compounds always represents a synthetic membered phosphetes,[ 39 ] 5-membered phospholes,[ 40 ] 6- challenge. membered phosphinines[ 41 ], 7-membered phosphepine[ 42 ]) as In the present minireview, we will focus on PAH structures well as the variety of bonding modes (3,3-P, 4,5-P, 2,3-P) incorporating a P atom and the impact of this heteroatom on the make this heteroatom highly versatile and adept to tune the physical properties of the PAH. In the past years, phosphorus physical properties of -systems and PAHs in particular. has turned out to be an excellent building block for the [22] construction of extended conjugated π-systems. For example, 2 3 the , -P=C double bond has matching ionization energies in all hitherto investigated systems with their C=C bonded [23] counterparts making phosphorus in conjugated π-systems a [24] “carbon copy”. It is worthy to mention that the unoccupied π*- levels are significantly stabilized with respect to the all carbon [ 25 ] analogues, thus for these compounds a narrower HOMO- LUMO gap is expected. The situation of the compounds with 3 3 , -P is rather complex. As isovalent hybridization is not [ 26 ] favoured for heavier elements, the phosphorus’ lone pair 3 3 retains a significant “s” character (consequently , - phosphorus has a large barrier to pyramidalization), and conjugation with the π-system is reduced. With enforced 3 3 [ 27 ] planarity of the , -phosphorus, an excellent conjugative [ 28 ] building block can be formed. The pyramidal phosphorus, however, has sigma orbitals with proper symmetry to overlap Figure 2. Reported “ortho-fused” phospholes and scope of this review (“peri- with the π-system, via hyperconjugative interaction. In case
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