Tailoring the Solid-State Fluorescence of BODIPY by Supramolecular Assembly with Polyoxometalates

A cationic boron dipyrromethene (BODIPY) derivative (1) has been successfully combined with two polyoxometalates (POMs), the Lindqvist-type [W₆O₁₉]^2- and the β-[Mo₈O₂₆]^4- units, into three new supramolecular fluorescent materials (1)[WO]·2CHCN, (1)[WO], and (1)[MoO]·DMF·HO. The resulting hybrid compounds have been fully characterized by a combination of single-crystal X-ray diffraction, IR and UV-vis spectroscopies, and photoluminescence analyses. This self-assembly approach prevents any π-π stacking interactions not only between the BODIPY units, responsible for aggregation-caused quenching (ACQ) effects, but also between the BODIPY and the POMs, avoiding intermolecular charge-transfer effects. Noticeably, the POM units do not only act as bulky spacers, but their negative charge density drives the molecular arrangement of the 1 luminophore, strongly modifying its fluorescence in the solid state. As a consequence, the 1 cations are organized into dimers in (1)[WO]·2CHCN and (1)[WO], which are weakly emissive at room temperature, and in a more compact layered assembly in (1)[MoO]·DMF·HO, which exhibits a red-shifted and intense emission upon similar photoexcitation.