Fluorescent properties of octacalcium phosphate with incorporated isophthalate ions

Octacalcium phosphate (OCP) crystals have a layered structure into which various carboxylate ions can be incorporated. Recent studies have been conducted to incorporate aromatic carboxylate ions into OCP to impart fluorescence. However, the fluorescent properties of OCP with incorporated isophthalate ions have not been investigated. In this study, we synthesized OCP with incorporated isophthalate ions, and investigated its fluorescence behavior. The interplanar spacing of OCP was expanded from 1.88 to 2.32 nm by incorporation of isophthalate ions. The absorption peaks derived from the incorporated isophthalate ions were detected by Fourier transform infrared spectroscopy. We found that the obtained OCP with incorporated isophthalate ions emitted strong fluorescence at 315 nm with excitation light at 280 nm and emitted weak fluorescence at 380 nm with excitation light at 313 nm. The characteristic feature of this fluorescent OCP was ultraviolet light emission, whereas the previously reported fluorescent OCPs emitted visible light. The results of this study are worthwhile for the design of OCP-based materials with various fluorescent properties.