A Large Starphene Comprising Pentacene Branches

Starphenes show promising optoelectronic properties. Notably, HOMO–LUMO energy gap presumably decreases with their increasing size, making larger homologues extremely desirable. Unfortunately, with the size, their instability and insolubility also increase, challenging classical synthetic ways. A new method has been developed, enabling synthesis of large starphenes in a quantity sufficient for their full characterisation and further applications.
Starphenes are attractive compounds due to their characteristic physicochemical properties that are inherited from acenes, making them interesting compounds for organic electronics and optics. However, the instability and low solubility of larger starphene homologs make their synthesis extremely challenging. Herein, we present a new strategy leading to pristine [16]starphene in preparative scale. Our approach is based on a synthesis of a carbonyl-protected starphene precursor that is thermally converted in a solid-state form to the neat [16]starphene, which is then characterised with a variety of analytical methods, such as 13C CP-MAS NMR, TGA, MS MALDI, UV/Vis and FTIR spectroscopy. Furthermore, high-resolution STM experiments unambiguously confirm its expected structure and reveal a moderate electronic delocalisation between the pentacene arms. Nucleus-independent chemical shifts NICS(1) are also calculated to survey its aromatic character.
This research has been funded in parts by foundation EXPERIENTIA, ERDF/ESF “UOCHB MSCA Mobility” (No. CZ.02.2.69/0.0/0.0/17 050/0008490), and has received funding from the EraNET Cofund Initiatives Quan-tERA under the European Union's Horizon 2020 research and innovation programme grant agreement ORQUID. This project has received financial support from the CNRS through the MITI interdisciplinary programs and JST-ERATO (No. JPMJER1903) and JSPS-WPI. Financial support is also acknowledged from the Spanish Ministry of Science and Innovation (MAT2016-78293-C6, PID2019-107338RB-C63), from the Basque Government (IT-1255-19), from the Spanish National Research Council (CSIC, COOPB20432), from the Euro-pean Regional Development Fund (ERDF) under the program Interreg V-A España-Francia-Andorra (contract no. EFA 194/16 TNSI) and from the European Research Council (grant agreement no. 635919). The authors thank Yannick Coppel (LCC-CNRS, Toulouse) for recording CP-MAS spectra, Jean-Francois Meunier (LCC-CNRS, Toulouse) for thermogravimetric analysis and Vladimir Vrkoslav (IOCB-Prague) for recording MS MALDI spectra.