Cationic Boron Formazanate Dyes*.

Incorporation of cationic boron atoms into molecular frameworks is an established strategy for creating chemical species with unusual bonding and reactivity but is rarely thought of as a way of enhancing molecular optoelectronic properties. Using boron formazanate dyes as examples, we demonstrate that the wavelengths, intensities, and type of the first electronic transitions in BN heterocycles can be modulated by varying the charge, coordination number, and supporting ligands at the cationic boron atom. UV-vis absorption spectroscopy measurements and density-functional (DFT) calculations show that these modulations are caused by changes in the geometry and extent of π-conjugation of the boron formazanate ring. These findings suggest a new strategy for designing optoelectronic materials based on π-conjugated heterocycles containing boron and other main-group elements.