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 β-[Mo8O26]4– units, into three new supramolecular fluorescent materials (1)2[W6O19]·2CH3CN, (1)2[W6O19], (1)4[Mo8O26]·DMF·H2O. The resulting hybrid compounds have fully characterized by a combination of single-crystal X-ray diffraction, IR UV–vis spectroscopies, photoluminescence analyses. This self-assembly approach prevents any π–π stacking interactions not only between BODIPY responsible for aggregation-caused quenching (ACQ) effects, but also POMs, avoiding intermolecular charge-transfer effects. Noticeably, POM units do act as bulky spacers, their negative charge density drives molecular arrangement 1+ luminophore, strongly modifying its fluorescence in solid state. As consequence, cations are organized dimers (1)2[W6O19]·2CH3CN which weakly emissive at room temperature, more compact layered assembly (1)4[Mo8O26]·DMF·H2O, exhibits red-shifted intense emission upon similar photoexcitation.