Akimitsu Narita

Abstract:

Nanostructures of graphene demonstrate a wide range of optical, electronic, and magnetic properties depending on their size and chemical structures, which renders them promising as next-generation carbon-based nanomaterials, e.g., for nanoelectronics, spintronics, photonics, and solar energy conversion. Large polycyclic aromatic hydrocarbons (PAHs) possess the nanoscale graphene structures and have demonstrated the unique optoelectronic and magnetic properties predicted theory, thus attracting renewed attentions as atomically precise nanographenes [1]. We have recently developed the synthesis of dibenzo[hi,st]ovalene (DBOV) as a nanographene with a combination of zigzag and armchair edges, which demonstrated high stability, strong red emission, and optical gain properties [2]. The post-synthetic edge-functionalization of DBOV could be achieved through regioselective bromination, enabling the introduction of various substituents for modulating the optoelectronic and photophysical properties. For example, functionalization of DBOV with two fluoranthene imide (FAI) groups induced red-shift of the absorption and emission bands, increase of the Stokes shift, and enhancement of the stimulated emission (SE) signals with significantly reduced excited state absorption, allowing the efficient lasing at 720 nm [3]. On the other hand, we have more recently synthesized other unprecedented nanographenes with armchair, zigzag, and fjord edges, such as dibenzo[a,m]dinaphtho[3,2,1-ef:1',2',3'-hi]coronene (DBDNC), showing nonplanar structures by the single-crystal X-ray [4,5]. Notably, DBDNC displayed a SE signal at 710 nm with a longer lifetime than that of DBOV, presumably due to the suppression of intermolecular interactions. These results provide a further insight into the relationship between the PAH structures and their photophysical properties, paving the way toward their photonic applications.