Facile synthesis of fluorescent heterocirculene analogues with tunable solubilities and optical properties†
Heterocirculenes are an interesting class of polycyclic heteroaromatic molecules having rigid and planar structures, which are promising in light of their potential applications for OLEDs, OFETs and so forth. Although their synthetic methods have been developed in some specific cases, a facile synthetic protocol of novel heterocirculenes with tunable properties is highly desirable. We herein report the unexpected formation of methoxy-substituted quasi-azacirculene and its conversion into unprecedented triazaoxacirculene. The structures and optical properties were comparatively studied. Remarkably, triazaoxacirculene is highly soluble in THF, acetone and DMSO mainly because of effective hydrogen-bonding of the NH moieties to these solvents. Their highly soluble nature in various solvents enabled us to study the solvent effects of these molecules. In particular, triazaoxacirculene displays a high fluorescence quantum yield of 0.72 in DMSO. Furthermore, enantiomeric separation of highly distorted quasi-azacirculene was successfully achieved by chiral HPLC. Thus, these novel heterocirculene derivatives are practically useful fluorescent nanographene-like molecules with intriguing optical properties.