Al₈ Cluster-Based Metal Halide Frameworks: Balancing Singlet-Triplet Excited States to Achieve White Light and Multicolor Luminescence

Luminescent metal clusters have attracted great interest in current research; however, the design synthesis of Al clusters with color-tunable luminescence remains challenging. Herein, an [Al-8(OH)(8)(NA)(16)] (Al-8, HNA = nicotinic acid) molecular cluster with dual luminescence properties of fluorescence and room-temperature phosphorescence (RTP) is synthesized by choosing HNA ligand as phosphor. Its prompt photoluminescence (PL) spectrum exhibits approximately white light emission at room temperature. Considering that halogen atoms can be used to regulate the RTP property by balancing the singlet and triplet excitons, different CdX2 (X- = Cl-, Br-, I-) are introduced into the reactive system of the Al-8 cluster, and three new Al-8 cluster-based metal-organic frameworks, {[Al8Cd3Cl5(OH)(8)(NA)(17)H2O]2HNA}(n) (CdCl2-Al-8), {[Al8Cd4Br7(OH)(8)(NA)(16)CH3CN]NAHNA}(n) (CdBr2-Al-8) and {[Al8Cd8I16(OH)(8)(NA)(16)]}(n) (CdI2-Al-8) are successfully obtained. They realize the color tunability from blue to yellow at room temperature. The origination of fluorescence and phosphorescence has also been illustrated by structure-property analysis and theoretical calculation. This work provides new insights into the design of multicolor luminescent metal cluster-based materials and develops advanced photo-functional materials for multicolor display, anti-counterfeiting, and encryption applications.