m-Phenylene linked macrocycle composed of electron-rich dithienogermole and electron-deficient tricoordinate boron units

Incorporation of non-conventional elements into π-conjugated systems is a powerful tool to control the electronic structures. In this work, electron-deficient tricoordinate boron units were combined with electron-rich dithienogermole units to provide an element-hybrid conjugated macrocycle with m-phenylene linkers. In contrast to the absorption spectra which were unaffected by solvent polarity, the element-hybrid macrocycle exhibited clear solvatochromism in the fluorescence spectra originating from the charge transfer (CT) transition between the dithienogermole and tricoordinate boron units. The addition of fluoride to the solution of the macrocycle resulted in the stoichiometric formation of tetracoordinate borate species. Interestingly, the fluorescence was intensified by the addition of fluoride, and the mechanism was confirmed by fluorescence spectroscopy and TD-DFT calculations. [Display omitted] •A conjugated macrocycle containing germanium and boron atoms was synthesized.•A CT transition between dithienogermole and tricoordinate boron units was observed.•Unusual fluorescence enhancement was seen in the fluoride titration experiments.