Progress in the Field of Cyclophosphazenes: Preparation, Properties, and Applications

This review article provides a comprehensive overview of recent advancements in the realm of cyclophosphazenes, encompassing their preparation methodologies, distinctive properties, and diverse applications. The synthesis approaches are explored, highlighting advancements in the preparation of these cyclic compounds. The discussion extends to the distinctive properties exhibited by cyclophosphazenes, including thermal stability characteristics, and other relevant features. Furthermore, we examine the broad spectrum of applications for cyclophosphazenes in various fields, such as coatings, adhesives, composites, extractants, metal complexes, organometallic chemistry, medicine, and inorganic chemistry. This review aims to offer insights into the evolving landscape of cyclophosphazenes and their ever-expanding roles in contemporary scientific and technological arenas. Future possibilities are emphasized, and significant research data shortages are identified.

Single Molecular Persistent Room-Temperature Phosphorescence and Circularly Polarized Luminescence from Binaphthol-Decorated Optically Innocent Cyclotriphosphazenes

Circularly polarized luminescence (CPL) features of BINOL-decorated cyclotriphosphazenes (CPs) are reported for the first time. The luminescence dissymmetry factor (glum ) of these compounds in chloroform solutions and polymethyl methacrylate (PMMA) thin films with wt 1 % doping concentrations are found to be 1.0×10-3 , and 2.9×10-3 , respectively. However, no CPL signal is observed for the pristine solids. The enantiomers (CP-(R)/CP-(S)) show ultraviolet photoluminescence (~350-360 nm) in solution and the solid state. These compounds show ~10 times larger absolute photoluminescence quantum yield (PLQY) than the simple BINOLs in the solutions state. In the solid state, CP-(R) shows larger PLQY than binaphthol-(R); in contrast, the S enantiomer shows lower PLQY than binaphthol-(S); this indicates that the isomer-dependent solid-state packing of these compounds plays a crucial role in controlling the PL. Thin films with more than 1 % doping concentration and pristine solids of these compounds do not show persistent room-temperature phosphorescence (pRTP) due to concentration-caused quenching. However, thin films with wt 1 % of these chiral emitters exhibit pRTP characteristics with a ~159-343 ms lifetime under vacuum. Theoretical calculations reveal that the cyclophosphazene acts as an optically innocent dendritic core, and the optical features of these compounds are dictated by the pendent BINOL chromophore.

Cyclo- and Polyphosphazenes for Biomedical Applications

Cyclic and polyphosphazenes are extremely interesting and versatile substrates characterized by the presence of -P=N- repeating units. The chlorine atoms on the P atoms in the starting materials can be easily substituted with a variety of organic substituents, thus giving rise to a huge number of new materials for industrial applications. Their properties can be designed considering the number of repetitive units and the nature of the substituent groups, opening up to a number of peculiar properties, including the ability to give rise to supramolecular arrangements. We focused our attention on the extensive scientific literature concerning their biomedical applications: as antimicrobial agents in drug delivery, as immunoadjuvants in tissue engineering, in innovative anticancer therapies, and treatments for cardiovascular diseases. The promising perspectives for their biomedical use rise from the opportunity to combine the benefits of the inorganic backbone and the wide variety of organic side groups that can lead to the formation of nanoparticles, polymersomes, or scaffolds for cell proliferation. In this review, some aspects of the preparation of phosphazene-based systems and their characterization, together with some of the most relevant chemical strategies to obtain biomaterials, have been described.