Synthesis and study of the electronic properties of heteroatom-containing polycyclic aromatic hydrocarbons – Heterographene

The electronic properties of all these new derivatives (in solution and in the solid-state) will be evaluated by means of UV-vis absorption, fluorescence and electrochemistry. A first key study will consist of determining the HOMO-LUMO gap of these compounds. This data will be compared with theoretical models (DFT calculations). The impact of the heteroatom (P vs Si vs Ge) will be carefully investigated. Considering the differences in reactivity/electronic properties of group 14 and 15 heteroles, replacing the P atom by a Si or Ge atom will drastically affect the properties of the PAHs. The impact of the supramolecular organization on the electronic properties will also be studied.
These investigations will allow us to determine the suitability of these derivatives for further incorporation into opto-electronic devices. Depending on their intrinsic properties, the most promising candidates will be tested as emitters in OLEDs or as an active-layer in n-type OFETs.

This project unambiguously showed that insertion of heteroatoms, and in particular P-atoms, allows tuning the properties of PAHs in the context of organic electronic (OLEDs for example).

This project opens new perspectives in the field of organic synthesis and pi-systems for oprtoelectronic applications.

The results of the projects were published in 10 peer-reviewed articles in the field of general chemistry (Chem. Eur. J. (x3), New J. Chem), molecular chemistry (Org. Lett., J. Org. Chem., Eur. JIC), or materials chemistry (ChemPhysChem, Mater. Adv.). This diversity nicely illustrates the impact of the project in various research fields.

Polycyclic aromatic hydrocarbons (PAHs), the molecular analogs of graphene, are of great potential for the development of efficient optoelectronic devices (Organic Solar Cells (OSCs), Organic Light-Emitting Diodes (OLEDs), Organic Field-Effect Transistors (OFETs)) in the field of plastic electronics. Molecular engineering of PAHs using organic/organometallic chemistry is crucial for these industrial applications. Therefore, the Heterographene project consists in preparing new organic semiconductors based on PAHs of various size and shape incorporating P, Si or Ge atoms. The introduction of heteroatoms in the polyaromatic structure will allow for tuning of the electronic properties of the compounds. This method relies on the use of C-P/C-Si/C-Ge bond formation in the final step of our multi-step synthesis. In case of synthetic problems, an alternative retrosynthesis, using the same synthons, is envisaged. This new approach will allow the use of the widely studied cyclodehydrogenation (Scholl reaction) as the graphenization step. This reaction was successfully used by Müllen et al. for the preparation of the largest graphene molecular analogs. Most importantly, it will be possible to introduce different heteroatoms from a single synthetic precursor.
This strategy will first be tested on a model compound (a small PAH such as phenanthrene), then applied to larger PAHs like benzocoronene or other functional polyaromatic scaffolds such as perylene diimides or naphthalene diimides. This strategy also offers the possibility to prepare poly-heteroatomic PAH scaffolds.
The presence of a planar extended pi-system and lateral chains in the same molecule as well as a coordinating atom in the case of P-PAHs, will allow supramolecular engineering using multiple interactions (pi-stacking, coordination bonding, van der Waals interactions…). In this context, several supramolecular structures (organogels, liquid-crystals…) will be prepared and characterized.
The electronic properties of all these new derivatives (in solution and in the solid-state) will be evaluated by means of UV-vis absorption, fluorescence and electrochemistry. A first key study will consist of determining the HOMO-LUMO gap of these compounds. This data will be compared with theoretical models (DFT calculations). The impact of the heteroatom (P vs Si vs Ge) will be carefully investigated. Considering the differences in reactivity/electronic properties of group 14 and 15 heteroles, replacing the P atom by a Si or Ge atom will drastically affect the properties of the PAHs. The impact of the supramolecular organization on the electronic properties will also be studied.
These investigations will allow us to determine the suitability of these derivatives for further incorporation into opto-electronic devices. Depending on their intrinsic properties, the most promising candidates will be tested as emitters in OLEDs, as acceptors in OSCs or as an active-layer in n-type OFETs.