Versatile Synthesis and Enlargement of Functionalized Distorted Heptagon-Containing Nanographenes

Highly distorted polycyclic aromatic hydrocarbons are predicted to be atractive goals in nanoscience owing to the new properties they can adquire. We have shown that a variety of functionalized distorted heptagon-containing nanographenes can be easily prepared from simple building blocks by a sequence of Co-catalyzed cyclotrimerization and cyclodehydrogenation reactions. The versatility of this strategy allows an easy subsequent enlargement of these nanostructures by Ni-catalyzed cross-coupling and final cyclodehydrogenation reactions. Soluble extended distorted nanographenes 1 and 2 containing heptagon and an edge-shared pentagon-heptagon combination have been synthesized. Highly distortion of the polycyclic backbone of 2 caused by non-hexagonal rings and helicene moiety was confirmed by X-ray crystallography. Experimental data reveal promising optical an electronic properties for distorted PAHs with long fluorescence lifetimes (up to 14.5 ns) and low band gaps (down to 2.27 eV). This straight and versatile synthetic strategy, the observed long fluorescence lifetimes and the small optical and electrochemical band gaps for the presented compounds may promote the future implementation of distorted graphene molecules in electronic devices.