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 [W 6 O 19 ] 2– and the β-[Mo 8 O 26 ] 4– units, into three new supramolecular fluorescent materials (1) 2 [W 6 O 19 ]·2CH 3 CN, (1) 2 [W 6 O 19 ], and (1) 4 [Mo 8 O 26 ]·DMF·H 2 O . 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) 2 [W 6 O 19 ]·2CH 3 CN and (1) 2 [W 6 O 19 ], which are weakly emissive at room temperature, and in a more compact layered assembly in (1) 4 [Mo 8 O 26 ]·DMF·H 2 O, which exhibits a red-shifted and intense emission upon similar photoexcitation.