Metallacycle-cored supramolecular assemblies with tunable fluorescence including white-light emission

Abstract

<p id="d6916280e214">Light-emitting materials have been widely studied for their promising applications in chemical and biological science. Here we report three phenanthrene-21-crown-7 functionalized fluorescent Pt(II) rhomboidal metallacycles which were then converted into fluorescent supramolecular oligomers by reacting with a bis-ammonium linker. One of these constructs shows concentration-dependent fluorescence in a wide color range, where orange emission at high concentration and blue emission at low concentration was observed. Moreover, at a concentration of 29 µM the same ensemble emits white light that has emerged from the integration of the complementary orange and blue color from the metallacycles and linker, respectively. This study shows how light-emitting materials can be obtained by the proper implementation of multiple orthogonal interactions in a single process. </p><p class="first" id="d6916280e217">Control over the fluorescence of supramolecular assemblies is crucial for the development of chemosensors and light-emitting materials. Consequently, the postsynthetic modification of supramolecular structures via host–guest interactions has emerged as an efficient strategy in recent years that allows the facile tuning of the photophysical properties without requiring a tedious chemical synthesis. Herein, we used a phenanthrene-21-crown-7 (P21C7)-based 60° diplatinum(II) acceptor 8 in the construction of three exohedral P21C7 functionalized rhomboidal metallacycles 1–3 which display orange, cyan, and green emission colors, respectively. Although these colors originate from the dipyridyl precursors 10–12, containing triphenylamine-, tetraphenylethene-, and pyrene-based fluorophores, respectively, the metal–ligand coordination strongly influences their emission properties. The metallacycles were further linked into emissive supramolecular oligomers by the addition of a fluorescent bis-ammonium linker 4 that forms complementary host–guest interactions with the pendant P21C7 units. Notably, the final ensemble derived from a 1:1 mixture of 1 and 4 displays a concentration-dependent emission. At low concentration, i.e., &lt;25 µM, it emits a blue color, whereas an orange emission was observed when the concentration exceeds &gt;5 mM. Moreover, white-light emission was observed from the same sample at a concentration of 29 µM, representing a pathway to construct supramolecular assemblies with tunable fluorescence properties. </p>